Research Strategies for the Sampling and Analysis of Organic and
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Thursday, July 10, 2003 .......................................................................................................... 4 WORKING TITLE:................................................................................................................. 4 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Findings and Recommendations of the OCEC International Workshop, March 3-5, 2003, Durango, Colorado.............................................. 4 Authors (bold=submitted to date) ............................................................................................ 4 PREFACE ...................................................................................................................................... 4 TOPICS .......................................................................................................................................... 5 •Definitions.............................................................................................................................. 5 •Standardization....................................................................................................................... 5 •Thermal and Optical Filter Analysis ...................................................................................... 5 •Organic Speciation and Sampling .......................................................................................... 5 •Carbon Physical Properties .................................................................................................... 5 •Innovative Instrumentation .................................................................................................... 5 APPLICATIONS ........................................................................................................................... 5 •Fundamental Science ............................................................................................................. 5 •Source Apportionment ........................................................................................................... 5 •Visibility................................................................................................................................. 5 •Climate ................................................................................................................................... 5 •Health ..................................................................................................................................... 5 •Soiling .................................................................................................................................... 5 Introduction ............................................................................................................................... 5 Applications of Carbon Measurements ................................................................................... 5 Summary of Knowledge (Watson put in notes. Others elaborate) .......................................... 7 Research Strategy .................................................................................................................... 7 RESEARCH STRATEGIES ........................................................................................................ 8 Definitions .................................................................................................................................. 8 •Establish an applications group to arrive at consensus. Elaborate terms needing to be defined. Use Currie references as starting point. May be different for different application groups. (Currie) ....................................................................................................................... 9 Standardization ......................................................................................................................... 9 •Applications community define acceptable levels of accuracy and precision and necessary carbon fractions. (Currie) ..................................................................................................... 10 •Establish a first-principles standard for in situ particles suspended in air and sampled onto substrates. (Arnott) ............................................................................................................... 10 Procedures and capabilities for generating material with reproducible carbon fractions and light absorption for filter samples (hexane soot, kerosene soot, John Holmes breakout group list) ............................................................................................................................................... 10 Slurries, nebulization, suspension, bulk material, isotopic doping. (J. McDonald) ............. 11 Registry of standards and standard-generating facilities. Tabulation of historically used standard materials for air quality and combustion science. ................................................... 11 •Estimate biases caused by interactions within complex mixtures. (Joellen Lewtas) .......... 12 Specify influential properties for sampling media and estimate consequences of deviations from the ideal. Develop practical acceptance testing methods. ............................................ 12 Registry of thermal and optical analysis protocols (Holmes list, Chow abstract) .................... 13 Essential operating parameters in analysis method to be defined (Holmes list) Source of content: Judy Chow, Helene Cachier and Jianzhen Yu. ........................................................ 14 •Create a framework for interlaboratory comparisons and data analysis. Numbers and types of samples, statistical comparison methods, resolving and understanding differences, specific definition of method. (J. Chow) ........................................................................................... 14 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop An examination of IMPROVE blank thermograms for consistency and indications of adsorption (generalize Kirchstetter example). ....................................................................... 14 Define methods to determine consistency (e.g., material balance, chemical extinction, sum of organic compounds, soluble less than total). Accounting for liquid water. Weighing and extinction budgets.................................................................................................................. 15 Thermal & Optical Filter Methods ........................................................................................ 20 •Calculate changes in transmission and reflectance during analysis. Bound the uncertainties of pyrolysis correction for different presumed situations. Specify some cases. Evaluate deviations for different sample loadings. (Kirk Fuller) ......................................................... 20 The differences between black carbon mass concentrations obtained by light transmission and thermal/optical methods.................................................................................................. 20 •Quantify changes in form of graphitic carbon and absorbance during different stages of heating (use Raman and infrared transmittance and reflectance spectrum). Do with standards and mixtures. (Moosmuller) ................................................................................. 21 •Create oxidation rates with Arrhenius diagrams for common metal oxides. Determine levels at which different minerals might interfere. Verify these by spiking ambient samples. (Fung) .................................................................................................................................... 21 •Quantify effects of different catalysts on different carbon fractions. (Fung) ...................... 21 Create simulated mixtures from different source material of known fractions. Determine the extent to which thermograms superimpose. .......................................................................... 21 Thermal & Optical Filter Methods ........................................................................................ 23 Quantify decomposition temperatures of sub-10 micron particle carbonates in pure form and in contact with other aerosol components. Determine the extent to which different carbonates interfere with other carbon fractions. .................................................................. 23 Generate filters with from same material with different loadings (light, grey, black) and quantify effects of initial loading .......................................................................................... 24 •Define alternative temperature fractions that minimize pyrolysis or to better mark source materials. (Judy Chow & Barb Z.) ....................................................................................... 25 •Evaluate initial steps (oxygen at 350, high vacuum, acidification, water through filter) prior to combustion to minimize pyrolysis. (Cachier) ................................................................... 25 •Quantify changes in carbon fractions that result from different methods of treating the filter prior to sampling. Melting fibers may have an effect. Opens up reactive sites. (Cachier) .. 26 •Quantify differences in carbon fraction evolved and pyrolysis caused by different durations at different temperature steps. (Cachier) .............................................................................. 26 •Add water soluble organic material as a fraction. Can use ion water extract. (Hansson) .. 26 Properties of Carbonaceous Aerosol ..................................................................................... 26 Tabulate physical and chemical parameters for identified aerosol materials (vapor pressure, indices refraction, densities, sizes, chemical formula, hygroscopicity, Van Hoff factor, surface tension, molecular weights, optical cross-section, morphology, fractal dimension, dominant size, toxicity) ......................................................................................................... 26 •Measure indices of refraction and densities of carbonaceous aerosol and standards. McMurry at Univ of Minnesota (Fuller) .............................................................................. 27 •Define experiments and modeling to describe and quantify effects of aerosol aging on relevant parameters. (Fuller) ................................................................................................ 27 Pyrolysis (are there parameters?) .......................................................................................... 27 •Microscopic examination of standard, source material, and ambient material for shape and composition. (Cary) .............................................................................................................. 28 Organic Speciation and Sampling.......................................................................................... 29 •Develop sample substrates that minimize uncertainty of vapor adsorption. (Cachier) ....... 29 •Identify and quantify organic compounds adsorbed on quartz filters. (Gundel) ................. 29 Page 2 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop •Develop, and evaluate the benefits of organic denuder technology for long-term networks. (Brook) .................................................................................................................................. 29 •Develop methods to identify and quantify new organic constituents. Figure out what is in the hump. NMR? (Zielinska) ................................................................................................ 29 •Develop methods to identify and quantify toxic components. (J. McDonald).................... 29 •Further quantify chemicals in different thermal fractions. (Zielinska) ................................ 29 •Quantify sensitivity of organic materials to environmental variables of the blank, in passive and active sampler, transportation, and storage. .................................................................... 29 Innovative Methods ................................................................................................................. 30 •Develop instrumentation and procedures for Raman scattering measurements. (Moosmuller) ............................................................................................................................................... 30 •Develop and test in-situ continuous measurement systems. (Cary) ..................................... 30 •Add more specific detectors to thermal evolution analyses (GC, MS, AED) (Fung). ......... 30 SCHEDULE ............................................................................................................................. 30 Page 3 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Saturday, February 06, 2016 DRAFT IN PROGRESS PROGRESS DRAFT IN IN PROGRESS DRAFT DRAFT IN PROGRESS DRAFT IN PROGRESS DRAFT IN PROGRESS DRAFT IN PROGRESS DRAFT IN PROGRESS DRAFT IN PROGRESS DRAFT IN PROGRESS WORKING TITLE: Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Findings and Recommendations of the OCEC International Workshop, March 3-5, 2003, Durango, Colorado For publication in the year 2003 Authors (bold=submitted to date) Peter Barber, Tina Bahadori, Hélène Cachier, Robert Cary, Judith Chow, Lloyd Currie, Sylvia Edgerton, Johann Engelbrecht, Kirk Fuller, Kochy Fung, Lara Gundel, Hans C. Hansson, George Klouda, Charles McDade, Jake McDonald, Hans Moosmuller, Marc Pitchford, Tim Richard, John Watson, Jianzhen Yu, Barbara Zielinska Preface This material is based upon work supported by the National Science Foundation under Grant No. 0233861. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. OCEC International Workshop Premises: a need exists to revisit fundamental definitions and concepts surrounding particulate carbon in the atmosphere. agreed upon and shared definitions, sampling and analysis methods, applied through interlaboratory comparisons are needed to advance atmospheric aerosol research worldwide. This documents contains recommendations for the advancement of sampling and analysis of organic and elemental carbon fractions in atmospheric aerosols. Recommendations reflect the views of the world’s leading scientists on what is needed in order to advance atmospheric aerosols research. The authors were participants of the OCEC International Workshop, held March 4-5, 2003 in Durango, Colorado, where they generated they began to articulate a vision of the direction research needed to go. The workshop, which is one of a series of planned workshops on a variety of subjects, represents the desire of members of the research community to tap into the potential for a more cooperative interaction among researchers government agencies and sponsors, and students in the interest of not only improving the science, but also to improve the manner in which research and interlaboratory communication is conducted, funded, and disseminated. In Page 4 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop addition, the organizers and participants have attempted to link discussion within the context of global climate, human exposure and health, and visibility. OTHERS? Topics (Overview text still to kome) •Definitions •Standardization •Thermal and Optical Filter Analysis •Organic Speciation and Sampling •Carbon Physical Properties •Innovative Instrumentation Applications (Overview text still to kome) •Fundamental Science •Source Apportionment •Visibility •Climate •Health •Soiling Introduction Instructions—Objectives: Be more explicit and limiting. Describe process to attain objectives. Overview of content. Rationale for organization of info. Applications of Carbon Measurements What do we want out of carbon measurements for each application? How are they related to other applications? One-page each. Page 5 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop –Fundamental Science-Hansson text still to kome –Source Apportionment-Watson text still to kome Visibility—Organic and Elemental Carbon Measurement Requirements for Visibility Effects and Federal Visibility Protection Regulatory Purposes Marc Pitchford The visual effects of atmospheric aerosol are related to their light scattering and absorptive properties. Light extinction coefficient is the fractional light loss per unit of distance through the atmosphere caused by scattering (reflectance) and absorption (conversion to heat). The light extinction coefficient is the sum of the light scattering coefficient and light absorption coefficient. The light scattering phase function describes the relative amount of light scattered as a function of angle to the initial direction of the light. These atmospheric optical properties can be directly measured. Visibility effects can be calculated using radiative transfer modeling from the atmospheric optical properties combined with lighting and scene information. However, to relate visibility effects to their causes, it is necessary to assess the extent to which the major particle species contribute to light absorption and scattering. Optical properties of particles depend on their size, shape, density and index of refraction. For particles that are composed of non-uniform mixtures of materials, the particle-specific index of refraction depends on the bulk characteristics of the components and the morphology of the mixture (i.e. the dimensions, shapes and locations of the various components within the particles). Mie Theory can be used to calculate the optical properties from such information. However, these detailed characteristics of particle size, shape, and mixture are rarely known. More typically, particles are sampled in several broad particle size ranges (e.g. PM2.5 and PM10) and subjected to various bulk chemical speciation analyses methods to determine the mass concentrations of the major species. Estimates of the light extinction coefficient contributions by the major aerosol species are calculated by multiplying the mass concentrations of each species by a dry extinction efficiency value and by a value related to relative humidity to account for the enhanced extinction caused by water vapor growth of the particle in the atmosphere. The various species-specific dry extinction efficiency values and water vapor growth as a function of relative humidity were developed from a combination of theoretical and empirical assessments. Comparing aerosol-calculated light extinction coefficient estimates against the directly measured atmospheric light extinction coefficient demonstrates the reasonableness of this approach. The dry extinction efficiency of EC is generally taken to be about two to three times higher than that of the next highest species extinction efficiency. The haziness index specified in the federal Regional Haze Rule is based on aerosol-calculated light extinction because it permits direct assessment of the aerosol species responsible for causing visibility impacts. Organic and elemental carbon are two of the six major species (also sulfate, nitrate, fine crustal and coarse mass) measured at the 110 monitoring sites of the IMPROVE Network used to track long-term visibility trends for the visibility-protected national parks and wilderness areas throughout the U.S. To serve the needs of the visibility effects and visibility protection communities OC/EC aerosol measurements should at a minimum: Page 6 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Separate and quantify the mass of highly absorbing particulate carbon material (EC) collected on the filter from the material that does not absorb light. Quantify the mass of the carbon material that does not absorb light (OC). Precision and accuracy of OC/EC quantification of +10% is adequate. Other useful capabilities include: Sample-specific factors to convert carbon mass of OC (and perhaps EC) to the mass of the carbonaceous compounds. Quantify the light absorption of the initial sample and as the various OC/EC materials are evolved from the filter. Provide an estimate of the water vapor growth factor for each sample or class of samples. Provide additional information that can be useful in identification of the composition and sources of the OC and EC carbonaceous materials. –Climate-Hansson text still to kome –Health-Bahadori text still to kome –Soiling-Chow text still to kome Summary of Knowledge (Watson put in notes. Others elaborate) (Overview text still to kome) –Definitions –Standardization –Thermal and Optical Filter Analysis –Organic Speciation and Sampling –Physical and Chemical Properties –Innovative Methods Research Strategy (Add to list. Explain what they sponsor, how projects are selected, applications) Potential Sponsors Electric Power Research Institute (EPRI) CMA Environmental Protection Agency (EPA) National Science Foundation (NSF) Page 7 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Department of Energy (DOE) Department of Defense (DOD) National Oceanic and Atmospheric Administration (NOAA) CRC European Commission National NSFs WMO API Southern Company Individual car companies o Ford o General Motors o Toyota o Honda National Park Service (NPS) Department of Transportation (DOT) Department of Agriculture (USDA) California Air Resources Board (ARB) National Institutes of Health (NIH) HEI RESEARCH STRATEGIES Prepare text describing project-level strategies using this list as a guide •Descriptive (short) title •Objectives •Describe benefits for different applications •Describe research approach •Time and resource requirements •Needed skills, facilities, and collaboration •Potential sponsors Definitions Tabulate definitions currently in use. Elaborate on terms used by different application groups. Identify which data bases and study results use which definitions. (Tim Richard) Carbon Elemental Carbon (EC) Black Carbon (BC) Organic Carbons (OC) Total Carbon (TC) Soot Black LAC CC Thermal Optical Carbon (TOC) Char Smoke Graphite Graphitic Fractions Blank Page 8 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Fullerene Soluble Extractable COHS Precision Diamond Water Solvent Bioavailable PEC (pyrolycized elemental carbon) •Establish an applications group to arrive at consensus. Elaborate terms needing to be defined. Use Currie references as starting point. May be different for different application groups. (Currie) Standardization Do we standardize by application (climate, visibility, health, compliance), or just use one method? o Question of doing air quality monitoring for compliance, only need ??? If we are going to standardize by knowing detail components for health, then we may want to break out for certain types of compounds. Visibility and climate are closely related. A number of breakout groups echoed the idea: “If we are going to do all of this monitoring, can we have one standardized method to comply with regulations, or are we going to go with specialization; i.e., four monitoring mechanism sitting side-by-side?” Do we develop a “one-size-fits-all” monitoring apparatus, or do we need four different ones for visibility, climate, health . . . . Visibility and climate may be similar and if we are monitoring for components of PM we would probably get the same info for visibility. It is a different situation with monitoring for health. Current monitors are for mass-based monitoring. Those who know monitoring best should provide views on this. Speciation of carbon side inorganic from organic separation. Monitoring is for compliance and that means mass right now. Should we form an expert panel to assess this issue? Such a panel, if it existed, could potentially include air-pollution and climate scientists who would look at technical merits of different methods, without getting into detailed technical aspects. They would examine several issues with overarching perspective. The future is a comparison between continuous and filter-based methods (from J. Holmes). (Text still to kome) Page 9 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop •Applications community define acceptable levels of accuracy and precision and necessary carbon fractions. (Currie) •Establish a first-principles standard for in situ particles suspended in air and sampled onto substrates. (Arnott) PAT SAYS THERE IS NOTHING TO WRITE ANYMORE ON THIS SUBJECT, PER EXPERIMENTS HE IS CONDUCTING. Procedures and capabilities for generating material with reproducible carbon fractions and light absorption for filter samples (hexane soot, kerosene soot, John Holmes breakout group list) Jake McDonald, PhD, Associate Scientist, Lovelace Respiratory Research Institute Objectives: 1) Identify or develop procedures to create reproducible and homogenous carbonaceous aerosol atmospheres of varying composition (including non-carbonaceous constituents). 2) Utilize these resources to collect identical filter-based samples that contain a range of organic/elemental carbon contents and compositions. 3) Create a repository of filters that come from these well-characterized and well-defined atmospheres that can be used as standard reference materials (SRMs) for evaluation and comparison of carbon analysis techniques. Benefits: While measurements of total carbon are generally consistent, the operationally defined organic/black carbon split that is obtained from TOA techniques can vary substantially between methods. This variation will change in magnitude both depending on the specific TOA method and the composition of the material on the filter (e.g. wood smoke versus diesel). This has important impacts on interpretations of monitoring data obtained relating to visibility, climate, and health. Due to debates over the operationally defined organic/black carbon split, it is unlikely that a standard method will be established. There is a need for the development of SRM’s that will allow different and emerging carbon analysis techniques to be evaluated in a systematic way. Since differences in the defined carbon split are composition dependant, it is important that these SRM’s consist of a (wide) range of compositions and include both “known” proportions of organic/black carbon and unknown but reproducible SRM’s from environmentally relevant mixtures that will be operationally defined. Research Approach Two categories of SRM’s should be developed: 1. Samples consisting of “known” organic/black carbon concentrations a. Production of pure black carbon via nebulization or spark discharge. b. Combine black carbon with synthetic organic carbon of modern origin (e.g. oleic acid) in different proportions i. Verify organic/black carbon split by isotopic analysis or chemical analysis. 2. Samples consisting of complex and different proportions of organic/black carbon. Page 10 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop a. Produce atmospheres with well defined and different materials generated from emission sources and doped with other components. Need to cover a range of organic/black carbon ratios and compositions. A working list: i. Diesel exhaust with varying engine loads to produce different organic/black carbon splits. ii. Wood smoke over different stove operational cycles (can be combined) to represent “real-world” compositions. iii. Gasoline engine exhaust with varying engine loads to produce different organic/black carbon splits. iv. Tobacco smoke v. Meat cooking smoke vi. Coal derived carbon (ash from resuspension) vii. Mixtures of controlled proportions of modern and biomass derived carbon (examples): 1. Known proportions of wood smoke/diesel exhaust 2. Known proportions of gasoline/diesel exhaust 3. Known proportions of Wood smoke/gasoline exhaust Time/Resource/Facility Requirements To produce well characterized and well defined SRM materials of this nature it will require facilities with the ability to generate simple aerosols and aerosol mixtures in a controlled and reproducible fashion. The generation systems should be well-defined and, to the extent possible, be consistent with standardized methods of generating materials for emissions testing or other purposes. It is not required, but desired, that source based materials are from contemporary origins. It is essential that the laboratory executing the sampling program have experience in sound sampling methodologies to replicate filters. It is also essential that the research program have a quality assurance program that will meet the requirements of a NIST certification. This is a vital component to the result of this program. This program will likely involve collaboration from several laboratories to generate base-line analysis data with a range of techniques that illustrate similarities/differences among these materials. The comparison would be similar to the frame-work that went into certifying the carbon content of the NIST SRM 1649a. Potential sponsors As indicated earlier, the quantitative assessment of differences/similarities among TOA techniques is important to several research disciplines, including health (EPA, HEI, NIEHS, DOE), visibility (e.g. NPS), and climate (e.g. NOAA, EPA, DOE). Slurries, nebulization, suspension, bulk material, isotopic doping. (J. McDonald) Registry of standards and standard-generating facilities. Tabulation of historically used standard materials for air quality and combustion science. (Tim Richard to develop initial format to fill in content) Two ways to look at standards: Compliance standards and standardized sampling methods. Page 11 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Sources of information: National Ambient Air Quality Standards program (NAAQS). Under the Clean Air Act, EPA is required to review NAAQS every five years to see if changes are necessary. Three common monitoring methods: Improve (Chow & Watson), NIOSH, and Supersite (Paul Solomon and Rich Scheffe). Air quality OAQPS list standards (Bachmann? et al.). Also, look in Process Criteria document. Third standard: Profiles, standard materials (Currie). Ran through tests that we know what properties are and know how well monitoring instruments perform. Judy Chow: PM source profiles. •Estimate biases caused by interactions within complex mixtures. (Joellen Lewtas) Specify influential properties for sampling media and estimate consequences of deviations from the ideal. Develop practical acceptance testing methods. Charles McDade, University of California, Davis, 3/14/03 Objectives are to: identify desirable properties of sampling media that will lead to accurate OC/EC determinations; identify undesirable properties that can cause bias or measurement artifacts, and estimate their influence; develop practical acceptance testing methods for screening out undesirable properties and for quantifying deviations from ideal behavior. The results of this project will provide: improved knowledge of sampling media properties and their effects on OC/EC quantification; recommendations on standard sampling media to be used; a basis for comparing results from measurements where different media are used. Most sampling networks use quartz filters for collecting particles, but filter properties can differ between manufacturers and among lots from the same manufacturer. There are two principal attributes of filters that influence their ability to yield accurate concentrations of airborne carbonaceous material: 1) blank levels (impurities in the filter material); and 2) varying capacity for adsorbing gaseous organic material. Blanks are important in the measurement of EC as well as OC, but adsorbing properties are important for OC measurements only. Furthermore, there are differences in the materials used by various researchers to quantify positive and negative gaseous artifacts. Many researchers use quartz afterfilters (the same material as the particulate filter), whereas others use a variety of sorbent materials Laboratory and field studies can be conducted to amplify existing knowledge regarding these topics, especially to better understand the varying capacities of materials to adsorb organic gases. Page 12 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Most laboratories currently conduct acceptance tests to identify contamination in blank filters. These tests are rather straightforward, and involve analyzing new unexposed filters by standard methods such as TOR. Acceptance testing for adsorbing capacity are uncommon, but nevertheless important. Such tests will need to be designed to determine which gases are commonly adsorbed (i.e., which ones are important in the atmosphere), and laboratory methods will need to be developed to expose new filters to a prescribed atmosphere and then to evaluate how much was adsorbed. This project will require field and laboratory testing of a variety of media, and could require a range of sampling equipment to accommodate different media sizes and shapes, as well as different flowrates. This project will require laboratory facilities and expertise to expose media to known and measurable quantities of gaseous organics, and to generalize or simplify those techniques for use elsewhere. Potential sponsors include network operators (e.g., EPA/STN, NPS/EPA/IMPROVE) to provide tests and procedures that they can apply routinely, and media manufacturers who have an interest in the purity and applicability of their products. Registry of thermal and optical analysis protocols (Holmes list, Chow abstract) Thermal evolution protocols are often referred to as Thermal Optical Reflectance (TOR) or Thermal Optical Transmission (TOT) as if the method by which pyrolysis is assessed is the major difference. Although some differences exist between optical pyrolysis detection, these are secondary to the evolution temperatures, atmospheres, and durations for defining carbon fractions. Large numbers of OC and EC measurements have been reported by the following thermal and optical methods: Method Reference 1) Oregon Graduate Institute thermal optical reflectance 2) IMPROVE TOR and thermal optical transmittance (TOT) 3) NIOSH TOT 4) STN TOT 5) Aerosol Characterization Experiments in Asia (ACEAsia) TOT 6) Hong Kong University of Science and Technology UST-3 7) Meteorological Service of Canada’s MSC1 TOT 8) General Motors Research Laboratory two temperature 9) Brookhaven National Laboratory two temperature 10) Japanese two temperature 11) thermal manganese oxidation 12) R&P two temperature 13) Lawrence Berkeley Laboratory continuous (TOR) (Huntzicker et al., 1982) (Chow et al., 1993, 2001) (NIOSH, 1999) (Mader et al., 2001) (Yang and Yu, 2002) (Sharma et al., 2002) (Cadle et al., 1980) (Tanner et al., 1982) (Mizohata and Ito, 1985) (Fung, 1990; Fung et al., 2002); (Rupprecht et al., 1995); (Novakov, 1982) Page 13 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop temperature ramp 14) French pure oxygen combustion 15) German VDI (Cachier et al., 1989a, 1989b) (Verein Deutcher Ingenieure, 1996, 1999) 16) Other Results of method comparisons among many laboratories provide ambiguous results owing to subtle differences in the methods applied and the samples included in the comparison (Sadler et al., 1981; Bennett and Patty, 1982; Cadle and Groblicki, 1982; Cadle et al., 1983; Edwards et al., 1983; Groblicki et al., 1983; Szkarlat and Japar, 1983; Japar, 1984; Japar et al., 1984; Adams et al., 1989, 1990; Powell et al., 1989; Cadle and Mulawa, 1990; Countess, 1990; Hanson and Novakov, 1990; Hering et al., 1990; Lawson and Hering, 1990; McMurry and Hansen, 1990; Turpin et al., 1990, 1997; Ruoss et al., 1991; Horvath, 1993, 1997; Petzold and Niessner, 1995a, 1995b; Hitzenberger et al., 1996, 1999; Huffman, 1996; Guillemin et al., 1997; Birch, 1998; Reid et al., 1998; Allen et al., 1999; Lavanchy et al., 1999; Babich et al., 2000; Tohno and Hitzenberger, 2000; Chow et al., 2001; Moosmüller et al., 2001; Schmid et al., 2001; Arnott et al., 2002; Currie et al., 2002; Watson and Chow, 2002; Fung et al., 2002). Essential operating parameters in analysis method to be defined (Holmes list) Source of content: Judy Chow, Helene Cachier and Jianzhen Yu. •Combustion atmospheres •Temperature ramping rates •Temperature plateaus •Residence time at each plateau •Optical monitoring configuration and wavelength •Standardization •Oven flash •Sample aliquot and size •Oxidation (C to CO2) catalyst •Evolved carbon detection method •Carrier gas flow through or across the sample •Location of the temperature monitor relative to the sample •Create a framework for interlaboratory comparisons and data analysis. Numbers and types of samples, statistical comparison methods, resolving and understanding differences, specific definition of method. (J. Chow) An examination of IMPROVE blank thermograms for consistency and indications of adsorption (generalize Kirchstetter example). Charles McDade, UC Davis, 3/14/03 Objectives are to: 1) Determine the variability of IMPROVE blank thermograms between filter lots and between sites. Page 14 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop 2) Estimate the uncertainty imposed by changing lots during a measurement period (quarter or month). 3) Reevaluate the uncertainty imposed by sampling afterfilters at 6 sites and applying the median value to the entire network. 4) Better understand the mechanisms by which organic gases are bound to filters, such as the multiple binding energies proposed by Kirchstetter. The results of this project will help to: 1) Determine whether an approach is needed that would require distinct breaks between filter lots. 2) Apply Kirchstetter’s analysis to TOR thermograms. 3) Better understand, and also reduce, the uncertainty in applying afterfilter artifact corrections. Kirchstetter (Atmos. Environ., 35, 1663-1671, 2001) has shown that different quartz filter lots exhibit different affinities for gaseous organic material. Consequently, artifact corrections using afterfilter values can vary considerably and can significantly influence the reported ambient OC concentrations. Kirchstetter’s results are based on the Novakov EGA thermal analysis method. There is a need to investigate similar differences that might be observed using the more commonly applied TOR method, and to determine how lot-to-lot differences should be incorporated into the IMPROVE data interpretation (artifact correction, in particular). TOR thermograms exist for blanks and afterfilters for a variety of IMPROVE filter lots exposed over a period of years. This work would entail examining this historical record and evaluating differences among lots, as well as from site to site. It will be particularly instructive to examine the standard deviation of afterfilter values within periods when lots changed. It will also be necessary to revisit the uncertainty imposed by applying the median afterfilter value to the entire network during each defined period. In addition to work with ambient samples, Kirchstetter also exposed filters to single compounds or groups of compounds (hexadecane, hexanol, etc.) and evaluated the EGA thermograms. Among other findings, he found that many compounds exhibit more than a single binding energy, so that the same compound may be apparent at different temperatures on a single thermogram. Similar work needs to be performed for TOR thermograms. Much of this work can be performed using existing IMPROVE thermograms. Some additional laboratory work will be required to expose filters to known amounts of single compounds and then to conduct the TOR analyses. This work would most likely be done at UC Davis and DRI. Since the filters are from IMPROVE, the most likely sponsors would be the existing IMPROVE sponsors. Define methods to determine consistency (e.g., material balance, chemical extinction, sum of organic compounds, soluble less than total). Accounting for liquid water. Weighing and extinction budgets. Richard Countess, Countess Environmental, Westlake, California Ideally, there will be a consistency in the methodology employed by different investigators to perform a chemical mass balance or a chemical extinction budget. Sadly, this is not the case in Page 15 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop many instances. It is important that all underlying assumptions are well documented, and that the assumptions should be scientifically robust. Material Balance Performing a chemical mass balance (also called material balance) involves summing up the concentrations of all measured particulate species and comparing this result with the gravimetrically measured mass concentration. Difference between these two parameters (i.e., sum versus measured mass) yields an estimate of the concentration of unmeasured species such as oxygen associated with soil related elements; oxygen, nitrogen and hydrogen associated with organic aerosol species; and liquid water absorbed on hygroscopic particles. Reconstructing mass concentrations involves applying different multipliers to the measured species to account for the unmeasured species. There are three published formulas for calculating the concentration of geological material, also called soil, (J. Chow, private communication, 9/24/02), namely: Soil = 1.89Al + 2.14Si + 1.4Ca + 1.43Fe (Solomon et al., 1989) Soil = 1.89Al + 1.57Si + 1.2K + 1.4Ca + 1.43Fe (Zhang et al., 1994) Fine soil = 2.2Al + 2.49Si + 1.63Ca + 2.42Fe + 1.94Ti (IMPROVE, 2002). The last equation has been used by U.C. Davis and the National Park Service (NPS) to estimate soil contributions for PM2.5 samples acquired from the IMPROVE network. This equation has recently gained more attention because it is being used as a standard way of calculating chemical light extinction to determine increments of reasonable progress under the Regional Haze Rule (USEPA, 2001). It should be pointed out that the article on reconstructed PM2.5 mass published by Sisler and Malm (2000) contains an incorrect multiplier for Si, namely 2.19. The concentrations of the major chemical components of interest for the IMPROVE network are calculated as follows (Watson, 2002): ammonium sulfate, (NH4)2SO4 = 4.125 [S] ammonium nitrate, NH4NO3 = 1.29 [NO3] organics =1.4 [OC], where OC = organic carbon measured by the TOR analysis scheme light-absorbing carbon (LAC, also called soot) = EC, where EC = elemental carbon measured by the TOR analysis scheme soil (also called fugitive dust) =2.2 [Al]+2.49 [Si]+1.63 [Ca]+2.42 [Fe] + 1.94 [Ti] Several assumptions are made regarding the unmeasured nitrogen, hydrogen, and oxygen associated with different chemical compounds. The 4.125 multiplier for sulfur (S) assumes that all S is in the form of ammonium sulfate where any sulfuric acid has been completely neutralized by ammonia; unmeasured oxygen supplies a factor of three, which is further modified by a factor of 1.375 to account for unmeasured ammonium. The 1.29 multiplier for nitrate assumes that all nitrate is present as ammonium nitrate. Obviously, the presence of any sodium nitrate, which tends to be in the coarse size mode, will affect the accuracy of the multiplier used for nitrate. The multipliers used for the major elements associated with soil assume that the soil composition is 100% Al2O3, SiO2, CaO, and TiO2 with equal amounts of FeO and Fe2O3. The protocol used for the IMPROVE network specifies a secondary correction of 0.6(Fe) to estimate the K 2O content. Potassium (K) measured by XRF is not used directly because it includes both potassium of geological origin as well as potassium originating from vegetative burning. According to Sisler and Malm (2000) these assumptions yield a reconstructed mass concentration that accounts for 86% of the total soil mass. Thus, these authors recommend applying an additional factor of 1.16 to account for other species associated with soil (e.g., MgO, Na2O, H2O, and CO2). This Page 16 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop additional factor of 1.16 is reflected in the multipliers for the key soil related elements included in the equation above. In his analysis of PM10 and PM2.5 samples from the California Regional Particulate Air Quality Study (CRPAQS), Countess (2002) did not use this additional factor of 1.16 since the reconstructed mass concentrations were already equal to or larger than the actual measured mass concentrations without this additional correction. Countess (2002) calculated reconstructed mass concentrations using the conventional factors of 1.4 for organic carbon (to account for unmeasured hydrogen and oxygen), 1.29 for nitrate (that assumes that all the nitrate is present as ammonium nitrate), and 1.38 for sulfate (that assumes all the sulfate is present as ammonium sulfate), plus the following multipliers for the major elements associated with soil: 1.89 for aluminum, 2.14 for silicon, 1.40 for calcium, 1.87 for iron, and 1.67 for titanium which assumes that the major elements associated with soil are present as their predominant oxides (i.e., Al 2O3, SiO2, CaO, K2O, and TiO2, with iron present as an equal mixture of FeO and Fe2O3). The factor for iron includes a term to account for potassium associated with soil, K soil, where Ksoil is equal to the total amount of potassium measured by XRF, Ktotal, minus the water soluble potassium, Ksol, associated with vegetative sources measured by Atomic Absorption, and Ksoil = 0.428 Fesoil based on a regression analysis of PM10 Minivol data for these two elements. Reconstructed mass also included the other measured chemical species: elemental carbon, water soluble sodium and potassium, and the balance of the 40 elements measured by XRF excluding Na and S. Countess (2002) found that calculated reconstructed PM10 and PM2.5 mass concentrations were systematically higher than the measured PM10 and PM2.5 mass concentrations. This was especially noticeable for concentrations below 30 g/m3. The sum of species (a parameter that excludes any multipliers to account for unmeasured species) was also systematically higher than measured mass concentrations for concentrations below 15 g/m3. For concentrations >30 g/m3 the reconstructed mass concentration for most records was within 10% of the reported mass values. The 1.4 multiplier applied to OC measurements to account for unmeasured chemical species associated with organic compounds is traceable to two samples taken in the early 1970s in Pasadena, CA. Turpin and Lim (2001) have recommended that a multiplier of 1.6 be used for urban organics, a multiplier of 2.1 be used for non-urban organics, and a multiplier of 2.2 to 2.6 be used for samples affected by large contributions from vegetative burning. Multipliers of 1.6 and 2.3 for non-polar and polar organic compounds, respectively, are recommended by Zielinska (2003). Thus, the 1.4 multiplier is a lower limit more applicable to fresh hydrocarbon emissions. Soot is set equal to unity times EC, although soot is a complex mixture of carbon and other species such as O, H, S, and N. ARB calculates reconstructed mass concentrations using a multiplier of 1.29 for nitrate, 1.38 for sulfate, 1.4 for OC, 1 for EC, 1.89 for aluminum, 2.14 for silicon, 1.4 for calcium, 1.43 for iron (which assumes that iron is present solely in the form of Fe2O3 rather than the more generally accepted assumption of an equal mixture of FeO and Fe2O3), and does not include a multiplier for potassium or titanium to account for oxygen associated with K2O and TiO2 (K. Turkiewicz, private communication, 9/17/02). According to the statement of work for two of ARB’s CRPAQS data analysis contractors, DRI and ENSR, the multipliers employed by ARB will be used for calculating reconstructed mass concentrations for particulate samples from the CRPAQS network (R. Hackney, private communication, 9/5/02). According to Watson (private communication, 5/31/02), the reconstructed mass concentrations during the summer can be higher than the measured mass concentrations because: (1) the organic carbon measured on the quartz filter is positively biased (this is especially a problem if the Page 17 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop ambient organic aerosol concentrations are low and organic vapors are absorbed by the quartz filter making the organic carbon higher than it is); (2) some of the particle organics may have evaporated from the Teflon filter making the mass lower than it should be; and/or (3) the XRF self-absorption corrections used for Al and Si may be larger than they need to be based on the size distribution assumed by DRI for soil particles. If the soil particles are actually smaller than the size distribution assumed by DRI, then these low atomic number elements don't absorb as much of the emitted x-rays and their reported concentrations are too high. DRI often finds the reconstructed mass during the winter to be lower than the measured mass because: (1) some of the hygroscopic particles (e.g., ammonium nitrate) still contain unmeasured liquid water; and/or (2) more polar organic compounds from wood burning and secondary aerosols may have more oxygen atoms than are assumed by the 1.4 multiplier. Countess (2002) found that the ratio of reconstructed mass to measured mass for particulate samples from the CRPAQS network to be dependent on concentration rather than season. The filter-based measurements used for ambient monitoring networks such as IMPROVE and CRPAQS are state of the art but suffer from the same difficulties as all filter-based technologies: (1) particles change after they are removed from the atmosphere; (2) the filter interacts with the gases and particles that pass through it; and (3) particle deposits are small (usually less than 1 mg of mass), requiring low laboratory detection limits, and can be easily contaminated. PM2.5 and PM10 particle mass are measured gravimetrically on Teflon-membrane filters after equilibration at low relative humidity to remove most of the absorbed water. Even after this equilibration, some evidence of water in soluble particle deposits has been found, which is another reason that measured and reconstructed mass sometimes disagree for high sulfate and nitrate concentrations. DRI’s Level II validation scheme for filter analyses is based on evaluating the ratio of the sum of measured species (excluding Cl-, K+, and S,) to mass (J. Chow, private communication , 9/24/02). If the ratio exceeds 1 ± 2 sigma (where sigma is the propagated uncertainty), the sample is checked for the XRF/mass ratio, carbon/mass ratio, ion balance, SO4=/S ratio, Cl-/Cl ratio, and K+/K ratio. All suspect samples then are reweighed or reanalyzed. If the reanalyses show ratios still exceeding the acceptable range, then the sample results are flagged. Reconstructed Chemical Light Extinction The reconstructed chemical light extinction, bext (expressed in units of Mm-1), for particulate samples collected in the IMPROVE network is calculated as follows (Sisler and Malm, 2000): bext =3 f(RH)[(NH4)2SO4 + NH4NO3] + 4 [organics ] + 10 [LAC ] + 1 [fine soil] + 0.6 [coarse mass] + 10 The final term of 10 Mm-1 accounts for clear air Rayleigh scattering, and the coefficients are extinction efficiencies in units of m2/g. A relative humidity (RH) scattering enhancement factor, f(RH), for ammonium sulfate and ammonium nitrate is used to account for increased scattering efficiencies as these hygroscopic chemical species absorb liquid water and increase in size. Coarse mass is determined from the difference of PM10 mass and PM2.5 mass. The chemical light extinction budget assumes: (1) constant dry extinction efficiencies (i.e., the amount of light scattered or absorbed per unit mass concentration) of 3 m2/g for ammonium sulfate and ammonium nitrate, 4 m2/g for organics, 10 m2/g for soot, 1 m2/g for fine soil, and 0.6 m2/g for coarse mass; (2) ammonium sulfate and ammonium nitrate extinction efficiencies increase with increasing relative humidity (RH) according to a common growth curve, f(RH), based on their tendency to absorb liquid water, while relative humidity has no effect on the extinction efficiencies of other particles (It should be pointed out that water soluble organics may absorb Page 18 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop water, but the few experiments that exist have shown any uptake of water to be much lower than that for inorganic aerosol species]; (3) ambient samples have the soil composition specified in the IMPROVE protocol (IMPROVE, 2002), and organics use a multiplier of 1.4 for organic carbon (OC) to account for unmeasured hydrogen, oxygen, and other non-carbon species; (4) groundlevel filter samples represent the chemical composition of the atmosphere along the sight path when it is being viewed; and (5) the six components used to calculate chemical extinction do not interactively affect chemical extinction. The statement of work for one of ARB’s CRPAQS data analysis contractors, ENSR, states that the following extinction efficiencies will be used for calculating reconstructed light extinction (expressed in units of m2/g) for analyzing data from CRPAQS (R. Hackney, private communication, 9/5/02): 3[0.7/(1-RH)0.7] for ammonium sulfate and ammonium nitrate 4[0.7/(1-RH)0.2] for organics 10 for LAC 2 for fine soil 0.6 for coarse soil References Countess, R. J., 2002. “Quantifying the Contribution of Fugitive Geological Dust to Ambient PM10 and PM2.5 Concentrations in the San Joaquin Valley,” Final Report prepared for the San Joaquin Valley APCD, Countess Environmental, Westlake Village, CA, December. IMPROVE, 2002. Interagency Monitoring of Protected Visual Environments-Data Resources. National Park Service, Ft. Collins, CO. http://vista.cira.colostate.edu/IMPROVE. Sisler, J. F., and W. C. Malm, 2000. “Interpretation of Trends of PM2.5 and Reconstructed Visibility from the IMPROVE Network,” J.AWMA, 50: 775-789. Solomon, P.A.; Fall, T.; Salmon, L.G.; Cass, G.R.; Gray, H.A.; and Davidson, A., 1989. “Chemical Characteristics of PM10 Aerosols Collected in the Los Angeles Area. J. Air Pollution Control Assoc., 39(2):154-163. Turpin, B. J., and H. J. Lim, 2001. “Species Contributions to PM2.5 Mass Concentrations: Revisiting Common Assumptions for Estimating Organic Mass,” Aerosol Sci. Technol., 35: 602-610. U.S.EPA, 2001. Draft Guidance for Tracking Progress Under the Regional Haze Rule. Prepared by U.S. Environmental Protection Agency, Research Triangle Park, NC. http://vista.colostate.edu/IMPROVE/Publications/GuidanceDocs/guidancedocs.htm. Watson, J. G., 2002. “2002 Critical Review – Visibility: Science and Regulation,” J.AWMA, 52:628-713. Zhang, X.Q.; Turpin, B.J.; McMurry, P.H.; Hering, S.V.; and Stolzenburg, M.R., 1994. “Mie Theory Evaluation of Species Contributions to 1990 Wintertime Visibility Reduction in the Grand Canyon,” J.AWMA, 44(2):153-162. Zielinska, B, 2003. “Organic Carbon Concentration and Composition in Fine Particulate Matter Collected During ARIES Study,” presentation at International Workshop for the Development of Research Strategies for the Sampling and Analysis of Organics and Elemental Carbon Fractions in Atmospheric Aerosols, Durango, CO, March 3-5. Page 19 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Thermal & Optical Filter Methods •Calculate changes in transmission and reflectance during analysis. Bound the uncertainties of pyrolysis correction for different presumed situations. Specify some cases. Evaluate deviations for different sample loadings. (Kirk Fuller) The differences between black carbon mass concentrations obtained by light transmission and thermal/optical methods Peter Barber, Research Professor, Desert Research Institute Objectives are to: (1) evaluate the mathematical models that are used to convert light transmission (attenuation) measurements to black carbon mass concentrations; (2) investigate artifacts, such as reflectance, that may introduce erroneous light transmission results (reflectance appears as increased attenuation); (3) examine the thermal/optical methods to understand the relationship between the changes in optical transmission (and/or reflectance) and the thermal-induced changes in the physical characteristics of loaded filters; i.e., thermal desorption of organic carbon prior to the detection of CO2 produced by elemental carbon combustion. The role of carbonates and sulfates will also be considered. Since light interactions with filters are key to both methods, the results of the above work will provide the information necessary to understand the differences between black carbon mass concentrations obtained with the two approaches. If the observed differences between the two methods can be satisfactorily resolved, then this may strengthen the case for moving to straight optical techniques, a relatively rapid and inexpensive approach, to determine black carbon mass concentrations on filters. The research approach will begin with an evaluation of the limitations of existing optical models for simulating reflectance, absorption, and transmission by unloaded and loaded filters. This will likely result in the development of improved simulation models based on radiation transfer analysis, probably using fractal rather than spherical particles embedded in a multiple-scattering medium. Particular attention will be paid to the inverse problem, i.e., using measurements to infer the physical characteristics of the materials deposited on the filters. The complexity of the materials on the filters will likely require multi-wavelength approaches. These models will be used to better understand straight optical approaches to obtaining black carbon mass concentrations as well as to infer the time-dependent physical characteristics of the thermal/optical approach. The goal of this work is to resolve the differences between the two methods. Two sets of resources will be required – computational and laboratory. The computations can be run on a standard high-end PC. The laboratory work will involve controlled experiments with carbon analyzers and optical light scattering instrumentation, both with prepared filter samples. This work will require expertise in electromagnetic theory, carbon analysis, laboratory optics, and data analysis. Potential sponsors are network operators (e.g., EPA/STN and NPS/EPA/IMPROVE), the National Science Foundation and NOAA’s Office of Global Change, Page 20 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop owing to the widespread use of filter measurements for climate applications, and the Department of Energy, owing to its interest in the production of black carbon by inefficient combustion processes. •Quantify changes in form of graphitic carbon and absorbance during different stages of heating (use Raman and infrared transmittance and reflectance spectrum). Do with standards and mixtures. (Moosmuller) •Create oxidation rates with Arrhenius diagrams for common metal oxides. Determine levels at which different minerals might interfere. Verify these by spiking ambient samples. (Fung) •Quantify effects of different catalysts on different carbon fractions. (Fung) Create simulated mixtures from different source material of known fractions. Determine the extent to which thermograms superimpose. Evaluation of TOA Thermograms for Superimposed Source Samples Marc Pitchford, National Oceanic and Atmospheric Administration The objective of this work is to assess the extent to which individual carbonaceous source types can be separately identified when emissions from two or more are combined on the same filter sample. This work will support the appropriate use of TOA thermograms for source apportionment. Knowledge of the sources responsible for the major components of atmospheric aerosol, including OC/EC, are essential to technical understanding and policy decisions for health, visibility, global climate, and materials effects applications. Source-specific samples for carbonaceous aerosol (e.g. diesel exhaust, meat cooking, wood smoke, etc.) are known to produce distinctive thermograms. If these thermogram characteristics from specific source types are conserved during transport in the atmosphere and if the thermograms resulting from multiple source influence are simply superimposed in a composite sample thermogram, then source profile thermograms could be used with Chemical Mass Balance types of receptor modeling to apportion ambient sample thermograms. Even if the thermogram characteristics of a source sample age during atmospheric transport, it may be possible to use other receptor modeling methods (i.e. UNMIX, PMF, etc.) to identify source types if the atmospheric changes are consistent. However these other methods still require that thermogram characteristics from multiple sources superimpose additively. This work consists of collecting filter samples from a variety of carbonaceous sources on individual filters, and composite filters with known relative contributions from two or more distinctive sources (e.g. 20% meat cooking & 80% diesel). TOA analysis is used to generate thermograms that represent the individual source and the composite source samples. Data Page 21 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop analysis consists of assessing the degree to which the composite source samples can be represented by adding the appropriate contributions from the individual source sample thermograms. Additional work of this type could also involve spiking individual source and composite source samples with know amounts of non-carbonaceous aerosols (e.g. crustal material, various sulfate or nitrate compounds) that are common in atmospheric aerosol to assess matrix effects that might change the thermograms in a way that reduces their utility for source attribution. Resource requirements include facilities for source sampling of the major carbonaceous aerosol plus a capability to conduct TOA (ideally using both IMPROVE TOR and STN TOT methods, since these produce most of the ambient data available for source attribution). This research could be completed in a year if done by an organization with the required facilities and experience. Potential sponsors for this work include particle speciation network operators (EPA, NPS, etc.), carbonaceous source industry affiliated groups (DOE, DOT, API, Automotive industry, etc.) and application groups (visibility - Regional Planning Organizations, global climate - NOAA, NSF NASA, etc). Page 22 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Thermal & Optical Filter Methods Quantify decomposition temperatures of sub-10 micron particle carbonates in pure form and in contact with other aerosol components. Determine the extent to which different carbonates interfere with other carbon fractions. Reactions of Carbonate Minerals in Aerosol Samples Johann P. Engelbrecht, Desert Research Institute 2) Objectives are to: 1) Identify minerals commonly found in certain ambient aerosol sample suites. 2) Assess which mineral reactions could be taking place on the filter punch in the TOR carbon analyzer during the heating stages. 3) Establish to which extent mineral carbonates in the sample influence the TOR measurement of other carbon fractions. 4) Review the method for the quantitative analyses of mineral carbonates in aerosol filter samples. The results from this study will provide researchers and analytical laboratories with a better understanding of, and a more accurate methodology for the analyses of aerosols containing high percentages of carbonate soil dust. The additional mineralogical information, together with chemical results of aerosols can better distinguish amongst different soils. Knowledge of the mineral content of aerosols is of importance to global climate modeling, visibility studies, as well as health effects. The experimental procedure will involve the identification of the mineral phases in the original aerosol sample, the reaction products formed at various heating temperatures, as well as the measurement of gases such as CO2 being evolved at different temperatures. 3) Apparatus for the experimental work include: 1) 2) 3) 4) 5) Re-suspension chamber for the preparation of filter samples. XRF, AA, AC, IC for the chemical analyses of samples. TOR carbon analyzer for the measurement of carbonate and other carbon species. X-ray diffractometer (XRD) for the identification of mineral phases. Differential Thermal Analyzer (DTA) for the measurement of mineral phase transition and mineral reaction temperatures. 6) Thermo Gravimetric Analyzer (TGA) for the measurement of mass changes (e.g. CO2, H2O losses) at various temperatures. Items 1-3 are available at the DRI, while items 4-6 are facilities housed at the Bureau of Mines and the Department of Chemical and Metallurgical Engineering at UNR in Reno. Potential sponsors for mineral dust aerosol projects include SERDP (DoD, DoE, NSF) because of their concern for health, visibility and environmental effects of dust emissions due to military operations in the dry southwestern regions of the USA and other desert regions of the world, as well as NOAA for their interest in the effect of mineral dusts on global climate. Page 23 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Generate filters with from same material with different loadings (light, grey, black) and quantify effects of initial loading Evaluation of TOA Results as a Function of Filter Loading (Marc Pitchford, National Oceanic Atmospheric Administration) The objectives of this work are to assess the effects of filter loading on TOA analysis and thereby define an effective operational range for filter loading. The results of this work will provide design criteria for samplers and monitoring programs as a function of anticipated ambient concentrations. It will also provide data processing and user groups with criteria for assessing data quality and appropriateness for use in various applications. TOA is applied to filter samples with a wide range of sample loading despite having little knowledge of the effects of loading. Lightly loaded samples may be below detection limits or experience problems of poor precision due to issues such as adjustments for imprecisely known blank values. Heavily loaded filter samples may suffer from greater matrix effects (i.e. interactions of sampled material resulting in thermogram modifications), problem in the optical monitoring process due to thick/opaque samples, and/or insufficient time for the material to evolve at each temperature step of the TOA procedure. This work consists of collecting sets of replicate ambient, source and/or chamber generated aerosol filter samples with a wide range of sample loadings (i.e. from very lightly loaded to nearly clogged filters). These can be generated by filtering for the same period of time with samplers using a range of filter face velocities, sampling a constant aerosol source or chamber for various times using the same face velocities, or using a particle-free air dilution system to maintain the same filter face velocity and sample period but have different sample loading on the filters. These should include filter samples with mixtures of particles with various carbonaceous and inorganic materials, typical of those found in ambient and source sampling. Data analysis consists of comparing the thermograms from the replicate samples with different loading levels to identify the low and high loading conditions that produce essentially the same results. An acceptable operational range may depend on the mix of materials in the samples so the results may involve development of a set of operational conditions or some sample-specific means to assess the credibility of the TOA results (e.g. by examining some characteristics of the thermograms). Resources requirements include facilities for producing the replicate filters with various loadings and the capability to conduct TOA (ideally using both the IMPROVE TOR and STN TOT methods since they produce most of the ambient data in the U.S.). This work could be completed in one to two years depending on the availability of the appropriate facilities and whether preliminary results suggest that a simple operational range for various TOA methods is suitable, as opposed to a more complex procedure for determining sample-specific assessment of acceptable loading. Potential sponsors for this work are the particle speciation network operators (EPA, NPS, etc.) Page 24 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop •Define alternative temperature fractions that minimize pyrolysis or to better mark source materials. (Judy Chow & Barb Z.) •Evaluate initial steps (oxygen at 350, high vacuum, acidification, water through filter) prior to combustion to minimize pyrolysis. (Cachier) Model the optical effects on transmittance and reflectance pyrolysis corrections during thermal evolution analysis. Judith Chow, Desert Research Institute, Reno, Nevada 4) Objectives are to: 1) Understand optical differences between light absorbing particles in air and deposited on a filter. 2) Quantify potential biases in optical pyrolysis corrections. 3) Provide guidance for method characterization experiments. The results of this project will provide users of measurements from different methods with quantitative estimates of deviations from optical properties in the atmosphere and among the methods. A by-product will be computational tools (documented software) that can be used by others to evaluate deviations under user-defined situations. Several models of varying complexity can be applied to simulate how optical properties of the same particles might differ between their suspension in air, their deposition on different types of filters, and during a thermal/optical carbon analysis. A simple model can be applied to examine solid layers of different indices of refraction to simulate material deposited on the surface of and throughout different filter media. Parametric studies using this model will systematically vary with: 1) real and imaginary components of the refraction index to determine how reflectance and transmittance change with different aerosol mixtures and changing composition during thermal analysis; 2) location of a deposit within different parts of the filter to determine how transmittance and reflectance might change as adsorbed gases pyrolyze and how particle penetration within the filter affect the optical pyrolysis correction; 3) dependence of transmission and reflectance on wavelength of the incident light; 4) changes in reflectance and transmission as a function of filter loading; and 5) non-absorbing layers on top of and interspersed with absorbing layers. Parametric studies of concentric spheres can be modeled when they are in the air and when they are imbedded in a refractive medium such as a quartz-fiber filter. This will provide a more realistic description of how absorption efficiencies will change as an organic or inorganic shell around a carbon core evaporates or pyrolizes at different temperatures. Dipole and fractal models can better represent deviations from the assumption of spherical particles. Fresh emissions are often long-chain aggregates of many smaller particles in close proximity, and multiple scattering is expected. These may change shape during heating, with a consequent change in absorption efficiency. This project will require expertise in mathematically modeling, aerosol sampling and thermal evolution analysis, software engineering, and data analysis. The most complex models are computationally intensive, but they can be implemented on high-level workstations. Potential sponsors are network operators (e.g., EPA/STN, NPS/EPA/IMPROVE) to provide more realistic uncertainty estimates of their data, the National Science Foundation and NOAA’s Office of Global Change, owing to the widespread use of filter measurements for climate applications, and Page 25 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop the Department of Energy, owing to its interest in the production of black carbon by inefficient combustion processes. •Quantify changes in carbon fractions that result from different methods of treating the filter prior to sampling. Melting fibers may have an effect. Opens up reactive sites. (Cachier) •Quantify differences in carbon fraction evolved and pyrolysis caused by different durations at different temperature steps. (Cachier) •Add water soluble organic material as a fraction. Can use ion water extract. (Hansson) Properties of Carbonaceous Aerosol Tabulate physical and chemical parameters for identified aerosol materials (vapor pressure, indices refraction, densities, sizes, chemical formula, hygroscopicity, Van Hoff factor, surface tension, molecular weights, optical cross-section, morphology, fractal dimension, dominant size, toxicity) Sylvia Edgerton, Staff Scientist, Pacific Northwest National Laboratory There are so many compounds, so many mixtures, so many properties, that this subject really has to be an issue of setting priorities. Exactly which species are we most interested in and what properties? The topic is relevant but too vague to for a research plan. Perhaps we should compile or put together a compilation of these materials, starting with whatever material NIST is using and make sure that that is well characterized. Then, identify some way of estimating properties for mixtures. Objectives are to: 1) tabulate known physical and chemical properties (e.g. vapor pressure, indices of refraction, densities, sizes, chemical formula, hygroscopicity, Van Hoff factor, surface tension, molecular weights, optical cross-section, morphology, fractal dimension, dominant size, toxicity) for selected carbonaceous aerosol materials; and 2) compile a well-defined set of carbonaceous aerosol standards with specific and relevant physical and chemical properties; and (3) develop methods and models for estimating chemical and physical properties for mixed and aged aerosols. The results of this project will provide users with relevant information for measurements and modeling of atmospheric aerosol and estimating the impacts on human health and the environment. While there are many volumes (and libraries) of physical and chemical properties of materials available, many do not contain values relevant for atmospheric aerosol measurements (especially for carbon containing aerosols) or for estimating the impacts of aerosols on human health or climate change. Where aerosol toxicity is a concern, properties such as solubility, reactivity, partitioning coefficients, Page 26 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop biosorption, bioaccumulation, and other parameters may be of most interest. Where visibility and climate change are of interest, the optical properties of the aerosol are likely to be more important. Therefore, because this area of research is potentially so broad, proposed research is best targeted for specific purposes (i.e. health, climate, etc.) and with well-defined research outcomes. Defining physical and chemical properties through laboratory studies can be time consuming and expensive. Thus before such studies are initiated, it is recommended that priorities for measurement are established. Potential sponsors for research related to carbonaceous aerosols and human health are the National Institute of Environment Health Science (NIEHS/NIH) and the Environmental Protection Agency (EPA). For carbonaceous aerosols related to climate change, the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the National Oceanic and Atmospheric Administration (NOAA) are potential sponsors. For standards related research, the National Institute of Standards and Technology (NIST) is a potential sponsor. •Measure indices of refraction and densities of carbonaceous aerosol and standards. McMurry at Univ of Minnesota (Fuller) •Define experiments and modeling to describe and quantify effects of aerosol aging on relevant parameters. (Fuller) Pyrolysis (are there parameters?) Jianzhen Yu, Assistant professor, Hong Kong University of Science & Technology The objective is to identify the major parameters in affecting pyrolysis of atmospheric aerosol OC. Results from this project will guide us in selecting thermal analysis conditions that are favorable to charring minimization and therefore improves the accuracy of ECOC split. Correction of OC pyrolysis is necessary for EC and OC determination using thermal methods. The use of optical charring correction has improved the accuracy of EC and OC measurements in comparison with thermal methods that rely on temperature alone to differentiate EC and OC (Birch, 1998; Schimid et al., 2001). Ideally, all thermal/optical methods should converge on the same value for EC as a result of their common definition for EC; i.e., EC is the fraction of TC that accounts for the light extinction properties of the sample at the start of analysis (Fung et al., 2002). However, significant variation in measured EC concentrations was reported when the same lab analyzed filters using thermal methods that employ the same charring correction scheme but different thermal conditions (Yang and Yu, 2002; Schauer et al., 2003). This suggests that the charring correction scheme is one source for the EC and OC measurement uncertainties. The optical charring correction scheme assumes that EC formed through pyrolysis of OC, referred as PEC hereafter, and native aerosol EC have the same light absorption coefficient at the monitoring light wavelength. Yang and Yu (2002) have shown that such an assumption is not valid. They have further deduced that the degree of over or under-estimation of native EC is proportional to the degree of overlap between PEC and native EC. Consequently, minimization of pyrolysis would improve the accuracy of EC measurements in thermal/optical methods since less PEC means less overlap between PEC and native EC. This leads to the importance of understanding the factors affecting pyrolysis. Page 27 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Apart from chemical compositions of aerosol OC, there is evidence to show factors such as carbon loading on the filter, filter brand, and thermal analysis conditions (e.g., temperature, temperature ramping rate, residence time at each temperature plateau, combustion atmosphere) affect the amount of charring. However, systematic efforts are lacking in quantifying the effects of these factors on EC and OC measurements in ambient and source samples. Field studies can be conducted to collect ambient and source samples onto filters of different brands (e.g., Whatman, Pall-Gellman) and to collect the same aerosol materials at different flow rates to give various filter loadings for testing. Subsequent laboratory work involves manipulation of the thermal analysis conditions on a thermal/optical analyzer to observe variation of pyrolysis extent. This project requires expertise and equipment in aerosol sample collection and laboratory facilities for carbon analysis by thermal/optical methods. References: Birch, M. E. Analysis of Carbonaceous Aerosols: Interlaboratory Comparison, Analyst, 1998, 123, 851857. Fung, K.; Chow, J. C.; Watson, J. G. Evaluation of OC/EC Speciation by Thermal Manganese Dioxide Oxidation and the IMPROVE Method. J. Air & Waste Manage. Assoc. 2002, 52, 1333-1341. Schauer, J. J. et al., ACE-Asia Intercomparison of a Thermal-Optical Method for the Determination of Particle-Phase Organic and Elemental carbon. Environ. Sci. Technol. 2003, 37, 993-1001. Schmid, H., et.al. Results of the ‘Carbon Conference’ International Aerosol Carbon Round Robin Test Stage I. Atmos. Environ. 2001, 35, 2111-2121. Yang H.; Yu J.Z. Uncertainties in Charring Correction in the Analysis of Elemental and Organic Carbon in Atmospheric Particles by Thermal/Optical Methods, Eviron. Sci. Technol. 2002, 36, 5199-5204. •Microscopic examination of standard, source material, and ambient material for shape and composition. (Cary) Page 28 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop Organic Speciation and Sampling •Develop sample substrates that minimize uncertainty of vapor adsorption. (Cachier) •Identify and quantify organic compounds adsorbed on quartz filters. (Gundel) •Develop, and evaluate the benefits of organic denuder technology for long-term networks. (Brook) •Develop methods to identify and quantify new organic constituents. Figure out what is in the hump. NMR? (Zielinska) •Develop methods to identify and quantify toxic components. (J. McDonald) •Further quantify chemicals in different thermal fractions. (Zielinska) •Quantify sensitivity of organic materials to environmental variables of the blank, in passive and active sampler, transportation, and storage. Charles McDade, University of California-Davis, 3/14/03 Objectives are to: 1) identify the most common semi-volatile compounds present in organic particles, the variability of particle composition in time and space, and their physical properties related to evaporation and adsorption during the sampling process; 2) develop scientifically-based goals for sampling conditions, sampler temperature, and sample handling, designed to minimize artifacts due to evaporation of semi-volatile particles or due to adsorption of organic gases. The results of this project will help researchers to: 1) develop sampling and sample handling procedures that are based on specific knowledge of aerosol properties, not “best practice” as is common now; 3) minimize and better understand sampling artifacts. The sampling of particulate organic carbon can be influenced by positive artifacts (adsorption of organic gases by filters and collected particles) and by negative artifacts (evaporative losses of semi-volatile particulate material). Chemical speciation data will be vital to understanding the principal components of the typical aerosol and, consequently, their evaporative and absorptive properties. To obtain chemical speciation data will require special analytical lab studies beyond the routine TOR analyses, which provide thermally-defined components of the aerosol but not discrete chemical species. Once the main compounds are identified, a literature evaluation of their likely evaporative and absorptive properties will be needed. These findings can be tested by exposing filters to specific compounds (or groups or Page 29 of 30 Research Strategies for the Sampling and Analysis of Organic and Elemental Carbon Fractions in Atmospheric Aerosols: Recommendations from the OCEC International Workshop classes of compounds) under a variety of sampling and storage conditions. Variables should include sampler temperature, filter face velocity, sampling duration, time spent in the sampler following sampling, shipping conditions (cold or ambient), and storage conditions at the laboratory. The result will be a set of recommendations for avoiding evaporative and adsorptive measurement artifacts. Laboratory tests (and possible field work) will be required to expose filters to known amounts of single compounds (or groups or classes of compounds) under a variety of controlled conditions, and then to conduct the TOR analyses. This work could be performed under the auspices of an existing network, such as STN or IMPROVE, or at a university research lab. Potential sponsors include network operators (e.g., EPA/STN, NPS/EPA/IMPROVE) to provide recommendations on how to conduct their sampling, and sampler manufacturers, who may see a need to alter their control of sampler temperatures and flowrates. Innovative Methods •Develop instrumentation and procedures for Raman scattering measurements. (Moosmuller) •Develop and test in-situ continuous measurement systems. (Cary) •Add more specific detectors to thermal evolution analyses (GC, MS, AED) (Fung). SCHEDULE •Summary of findings. Watson 3/7. •Post PPTs on Website by 3/14 (T. Richard). •Example Research Description. Chow will send example by 3/7. •Send out requests for research descriptions (Richard-3/10). Ask for return by 3/17. •Reminders, check progress, hold conference call, and send emails by 3/21. •Application Descriptions 3/24. •Package to topic leaders by 3/28. •Return revisions by 4/14. •Announce first draft availability 5/12. Page 30 of 30
