Proposal: Tahoe Research Supported by SNPLMA Round 10
Title:
Particulate Emissions from Biomass Burning: Quantification of the
Contributions from Residential Wood Combustion, Forest Fires,
and Prescribed Fires
Primary theme and subtheme 3: Air quality and Meteorology
this proposal is responding to 3a: Impact and Control of Atmospheric Particulate Matter
Principal Investigator and
Daniel Obrist, PhD
Receiving Institution
Desert Research Institute, Division of Atmospheric Sciences
2215 Raggio Parkway, Reno, NV 89512
Phone: 775-674-7008
Fax: 775-674-7016
Email: dobrist@dri.edu
Co-Principal Investigator
Alan W. Gertler, PhD
Desert Research Institute, Division of Atmospheric Sciences
2215 Raggio Parkway, Reno, NV 89512
Phone: 775-674-7061
Fax: 775-674-7060
Email: alang@dri.edu
Co-Principal Investigator
Barbara Zielinska, PhD
Desert Research Institute, Division of Atmospheric Sciences
2215 Raggio Parkway, Reno, NV 89512
Phone: 775-674-7066
Fax: 775-674-7060
Email: Barbara.Zielinska@dri.edu
Grants Contact Person
Lycia Ronchetti, Business Manager
Desert Research Institute, Division of Atmospheric Sciences
2215 Raggio Parkway, Reno, NV 89512
Phone: 775-673-7411
Fax: 775-674-7016
Funding requested:
$ 225,594
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II. Proposal Narrative
A. Project Abstract
The goal of this study is to develop and use a specific characterization method to differentiate
between particulate matter (PM) contributions in the Lake Tahoe basin from residential wood
combustion, wildfires, and prescribed fires. Deposition of PM is an important source of
phosphorus (P) and sediment to Lake Tahoe, and leads to reductions in water clarity and
decreases atmospheric visibility in the basin. The relative importance of PM emissions from
various types of biomass combustion—i.e., domestic wood combustion, wildfires, and prescribed
fires—is mainly based on seasonal observations without direct confirmation by measurements.
We propose to develop a method to specifically characterize PM emissions from domestic wood
combustion, wildfires, and prescribed fire emissions by combining two of the most commonly
used biomass combustion tracers, soluble potassium (K+) and levoglucosan, with detailed
characterization of organic compounds (i.e., carbohydrates, anhydrosugars, lignin), and
particulate-bound mercury (Hg). These chemical PM fingerprints are expected to provide a
powerful tool for differentiation of PM emissions from different biomass combustion sources—
including in-basin versus out-of-basin contributions—and will possibly also allow for evaluation
of past fire history in the basin in soil and sediment records.
B. Justification Statements
Subtheme 3a, entitled“Impact and control of atmospheric particulate matter” of Round 10 of the
SNPLMA RFP lists particulate emission as a serious issue for both air quality and water quality
in the Lake Tahoe Basin. Previous studies have shown wood smoke to be a major contributor to
particulate matter (PM) levels in the basin (e.g., Engelbrecht et al., 2009); however, the relative
contributions of PM emissions from domestic wood combustion from fireplaces and woodstoves
versus forest fires and prescribed fires are uncertain, making emission management and control
strategies by agencies challenging. Knowledge of the contributions is critical to reduce visibility
impacts and particulate and phosphorous (P) deposition to the lake. This project provides a tool
for quantification of anthropogenic emission from domestic heating versus wildfire and
prescribed fire activities on particle loads in the basin by developing and applying novel PM
tracer techniques to differentiate between various sources. The proposed experimental approach
directly relates to “Identification of emission sources that cause visibility impairment in the
Basin, determine their respective contributions to visibility impairment, and compare the results
with the emissions inventory.”
C. Concise Background and Problem Statement
Deposition of PM has been implicated as an important source of phosphorus (P) and sediment to
Lake Tahoe (Cliff and Cahill, 2000), which lead to reductions in water clarity. In addition,
ambient PM is the cause of decreased atmospheric visibility (Hymanson and Collopy, 2009).
Comprehensive emissions inventories and source characterization studies for the Lake Tahoe
Basin are hence critical if agencies are to develop effective strategies to reduce the impact of PM
on water clarity and visibility. Several source characterization studies in the Lake Tahoe Basin
have addressed the issue of atmospheric PM, including a yearlong “Sampling and Analysis for
the Lake Tahoe Atmospheric Deposition Study” (LTADS; Chang et al. 2005, Dolislager et al.,
2009) conducted by the California Air Resources Board (CARB). CARB also funded the Desert
Research Institute to conduct the “Lake Tahoe Source Characterization Study” by Kuhns et al.
(2004), a study which was designed to characterize the chemical composition of the major
pollutant sources, and which provided a first estimate on mobile source contribution to
atmospheric pollutants based on fuel sales data, but emissions from other source categories have
not been quantified.
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A recent Lake Tahoe Source Attribution Study (LTSAS) conducted by Engelbrecht et al. (2009)
funded by the USDA Forest Service used the above-mentioned data sets for a comprehensive
determination of sources contributing to PM levels in the basin. They applied various techniques
to determine the sources of the observed PM. Results of Chemical Mass Balance (CMB) model
for the Sandy Way site are shown in Figure 1, showing that vegetative burning is a major source
of PM2.5 and PM10, especially during the fall and winter months. As part of this study, the authors
intended to test to what degree PM emissions stem from prescribed fires inside the basin and
wildfires outside of the basin, which they hypothesized to be minor sources, but results were
inconclusive. Based on observed temporal patterns, it is likely that significant amounts of PM
emissions originated from residential wood burning during fall and winter months, but
quantification of PM contributions from wildfires, prescribed fires, and domestic wood
combustion via on direct measurements or measured tracer signatures are lacking to date.
In another study, Gertler et al., (2008) developed a baseline emissions inventory within the Lake
Tahoe basin. In addition to the species commonly included (i.e., CO, PM10, NOx, VOCs, and
SO2), they included species that could impact water quality and visibility (i.e., PM2.5, NH3,
phosphorous [P], and phosphate [PO4]). Some key results from this study are that (i) there is a
strong seasonal dependence of emissions from mobile sources and residential fuel combustion;
(ii) PM10, PM2.5, P, and PO4 emission include area wide sources, particularly residential fuel
combustion and road dust re-suspension; and (iii) PM10 and PM2.5 emissions from residential fuel
combustion dominate over wildfire emissions by over a factor of 3, but these estimates are highly
uncertain since they are based on activity estimates and do not take into account meteorological
variables that affect ambient concentrations.
Hence, both preliminary emission inventories and in-depth analysis of pollution studies highlight
an important contribution of domestic wood combustion to PM loads in the Lake Tahoe Basin,
but it is unclear how in-basin domestic emissions relate to in-basin and out-of-basin PM
emissions from wildfires and prescribed fire activities. Characterization of the respective sources
is highly uncertain and currently not supported by direct measurements. Wildfire risk reduction
programs in the Lake Tahoe basin include prescribed fires as an important tool—addition to
mechanical and manual treatments—to reduce fuel loads in overstocked forest with dense brush
(e.g., North Lake Tahoe Fire District 2009). Without accurate quantification of domestic wood
combustion emissions in the Lake Tahoe basin and comparison to PM contributions to natural
wildfires and prescribed fire emissions, development of regulations and reduction strategies for
PM emissions by agencies and land managers will be impossible or highly challenging at best.
D. Goals, Objectives, and Hypotheses to be Tested
The goal of this study is to develop and use a specific characterization method to differentiate
between PM contributions to the Lake Tahoe basin from residential wood combustion, from
wildfires, and from prescribed fire emissions. We are focusing on PM2.5 emissions (i.e., particle
sizes with diameter smaller than 2.5 μm) since most combustion-related emissions occur in this
size fraction and it is the main fraction responsible for visibility degradation and human health
impacts. Common biomass combustion tracers used to characterize PM contributions in source
apportionment studies mainly include soluble potassium (K+) and monosaccharide anhydrides
such as levoglucosan, a product of the thermal degradation of cellulose. While these tracers are
excellent fingerprints of biomass combustion emissions, they generally are not specific to
emissions from wildfires, prescribed fires, or domestic wood combustion.
We propose to develop a novel method to characterizing PM emissions from domestic wood
combustion, wildfires, and prescribed fire emissions by combining two of the most commonly
used biomass combustion tracers (K+ and levoglucosan) with detailed analysis of carbohydrates,
anhydrosugars, lignin breakdown products, and particulate-bound mercury (Hg). It has been
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recently reported (Medeiros and Simoneit, 2008) that burning of green vegetation (simulated
wildfires) release higher amounts of polar/water-soluble organic compounds such as unaltered
carbohydrates in comparison with dry/dead vegetation and residential wood combustion
emissions. Methyl-inositols seem to be more abundant in conifer green vegetation whereas
deoxy-inositols in oak vegetation. In addition, the most abundant lignin breakdown products
released from green vegetation burning are 4-hydroxyphenyl–type compounds such as pyrogallol,
4-hydroxybenzoic acid and shikimic acid (observed mostly in the conifer smoke extracts), and not
methoxyphenols, as reported for dry vegetation burning. Thus, these organic biomarkers have a
potential to differentiate between emissions from different fuel types associated with wildfires,
prescribed fires, and residential wood combustion.
Hg is present in all natural systems and is known to be associated with biomass, but Hg levels
greatly differ among plant tissues with bole wood—the predominant fuel type in domestic wood
combustion—showing an almost complete lack of Hg. Other fuel types such as leaves,
understory, and surface litter organic horizons have substantial Hg loadings exceeding bole wood
concentrations by order of magnitudes (Grigal 2003, Obrist et al., 2009; see Figure 3). In
addition, it has been shown that low combustion intensities, specifically smoldering-phase
combustion which is an important phase during wildfires and dominates prescribed fires (Andreae
and Merlet, 2001) lead to very high levels of particulate-bound Hg levels in smoke plumes
(Friedli et al., 2003; Obrist et al., 2008). High intensity fires such as during domestic wood
combustion, on the other hand, show negligent particulate-bound Hg emissions since fuel Hg
almost completely emits in volatile, gaseous form. Hence, effects of fire intensities further
amplify expected “fuel-based” differences in particulate-bound Hg emissions between domestic
wood combustion and wildfires and prescribed fires.
Hypotheses:
(i) PM2.5 emission signatures of residential wood combustion will have lower amounts of polar
and water-soluble organic compounds and will differ in lignin breakdown products as
compared to prescribed fires and wildfires with their higher amounts green fuel sources.
There will be different emission signatures in regards to organic compounds also between
wildfires and prescribed fire emissions and between different types and sizes of fires.
(ii) PM2.5 emissions from wildfires and prescribed fires will show much higher ratios of
particulate-bound Hg to other common biomass combustion tracers as compared to PM
emissions from domestic wood combustion. Particulate-bound Hg emissions will also show
different patterns between wildfires and prescribed fires, with prescribed fire emissions
showing highest levels of Hg due to pronounced smoldering combustion phases and burning
of relatively green, fresh fuels.
(iii) A comprehensive combination of traditional biomass combustion tracers (K+, levoglucosan)
along with detailed characterization of organic compounds and particulate-phase Hg will
allow to specifically fingerprint emissions from domestic wood combustion, from wildfires,
and from prescribed fires in the Lake Tahoe basin. These tracer signatures will also be related
to underlying fire intensities, different types, sizes, and intensities of wildfires (e.g., groundfires versus canopy fires) and different forms of prescribed fires (e.g., different fire intensity,
slash pile sizes and configurations).
E. Approach, Methodology, and Location of Research
Location and timing of research: We propose to conduct a series of PM2.5 filter sampling
measurements across the Lake Tahoe Basin and in other locations in the Sierra Nevada mountains
to characterize PM composition of different biomass combustion sources. First, filter sampling
will be conducted in fall and winter in residential areas in the Lake Tahoe basin (i.e., Incline
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Village and in South Lake Tahoe) with the intention to specifically collect emissions from
domestic wood combustion. The use of the typical biomass combustion tracers (levoglucosan and
soluble K+) will allow to clearly pinpoint biomass combustion sources as compared to other
sources also present in residential areas. Secondly, PM will be collected during prescribed fires
in the Lake Tahoe basin. Pile burning of slash and forest residues from thinned trees and shrubs
has been adopted by most agencies in the Tahoe Basin (e.g. Lake Tahoe Basin Management
Unit). We will coordinate with agencies in regards to timing and location of planned prescribed
fires in the Lake Tahoe basin. So far, we have contacted Matt Busse from the U.S. Forest Service
who is a Co-Pi on an existing prescribed fire project entitled “Effect of pile burning in the Tahoe
Basin on soil and water quality”. This collaboration will allow us to relate PM emission
signatures to variables such as fuel volume and type, soil temperature, and others, which will be
evaluated as part of this project. Finally, we will collect filter sampling in areas affected by
wildfire emissions. Obviously, the occurrence of wildfires is highly unpredictable and sampling
will likely occur outside of the Lake Tahoe basin. We intend to collect wildfire plume emissions
from two different fires occurring in the Sierra Nevada mountain range with a similar vegetation
structure (i.e., pine forests) to that of the Lake Tahoe basin. The nature and extent of the wildfire,
the mixing of the smoke plume, distances to the fires, topography, and meteorological conditions
during wildfires will be highly unpredictable causing potential difficulties in collection of wildfire
smoke emission plumes. To address these difficulties, we propose the use of a highly mobile
volume sampler for this study to allow highly flexible sampling upon short notice in a variety of
possible sampling locations. The proposed medium-volume filter sampler can easily be loaded
on the back of DRI truck and is operated with a mobile power generator placed downwind of the
sampler. This mobile sampling flexibility will also be beneficial for characterization of PM
emission from prescribed fires from possibly remote sites in the Lake Tahoe basin.
Medium-volume PM filter sampling: Filters used for soluble K+, and particulate-bound Hg
characterization are 47-mm diameter Quartz fiber filters (Pall Life Sciences, Ann Arbor, MI).
Filters will be heat-treated prior to filter sampling at 900°C for at least 4 hours. Filters for PM
mass and organics will be sampled on pre-cleaned Teflon impregnated glass fiber (TIGF) filters
(Pall Life Sciences, Ann Arbor, MI). Filters will be loaded into two medium-volume (113 L min1), portable samplers (DRI constructed) equipped with 2.5 µm inlets. In total, we propose to
collect 60 filters for characterization of the respective emission profiles, with approximately 15
filters each for collection of PM from domestic wood combustion sources, prescribed forest fire
activities, and natural wildfire. Additional filters will be loaded under clean, ambient air
conditions for characterization of background PM levels and under mixed source conditions.
Analysis of levoglucosan, carbohydrates, and lignin breakdown products: Analysis of levoglucosn,
carbohydrates and lignin breakdown products (see Figure 2) will be performed in DRI’s Organic
Analytical Laboratory. TIGF filters will be extracted with methanol by accelerated solvent
extraction (Dionex ASE 300 Accelerated Solvent Extrator). The extracts will be evaporated by
rotary evaporation followed by moisture filtered ultra high purity (UHP) nitrogen blow down to
dryness and then pyridine, acetonitrile and BSTFA with 1% TMCS will be added. All samples
will be analyzed by gas chromatography interfaced with mass spectrometry (GC/MS) within 18
hours to avoid degradation by electron impact ionization GC/MS technique using a Varian CP3400 gas chromatograph with a model CP-8400 Auto-sampler and interfaced to a Saturn 2000 Ion
Trap Mass Spectrometer. The calibration solutions containing all compounds of interest will be
freshly prepared and derivatized just prior to the analysis of each sample set.
Gravimetric analysis and determination of soluble K+: Gravimetric filter analysis and gravimetric
analysis of PM mass will be conducted by DRI’s Environmental Analysis Facility. The facility
specializes in suspended particulate matter analysis and is used widespread throughout the world,
including the IMPROVE network. Gravimetric determination of PM mass will be conducted by
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Mettler Toledo MT5 Microbalance used to weigh filters to the nearest 0.001 milligram. To minimize
effects of environmental conditions, filters are equilibrated and weighed in a temperature and
humidity controlled environment laboratory. For analysis of soluble K+, quartz-filters will be
extracted in 15 ml sterile polystyrene tubes, sonicated, and shaken. A Varian SpectrAA 880 Double
Beam Atomic Absorption Spectrometer (Varian, Palo Alto, CA, USA) is used to analyze quartz filter
extracts for K+.
Determination of particulate-bound Hg: Extraction of the total particulate-bound Hg from filters
will be performed using quartz-fiber filter digestion with 10% BrCl in DRI’s Hg Analytical
Laboratory under clean-hood conditions. Hg analysis will be performed using SnCl2 reduction,
dual gold amalgamation, and cold vapour atomic fluorescence spectrometry detection in
accordance with US EPA Method 1631 “Total Hg in Water using Dual stage gold
precocentration”.
F. Relationship of the Research to Previous and Current Relevant Research
The proposed study builds upon a number of earlier studies conducted in the Lake Tahoe Basin.
As discussed in the recently released Air Quality Chapter of the Science Plan for the Lake Tahoe
Basin (Gertler et al, 2009), results form the IMPROVE monitoring conducted at South Lake
Tahoe and Bliss State Park have shown PM2.5 to be the leading cause of visibility degradation in
the basin. This finding prompted the TRPA to adopt standards to reduce wood smoke emissions
by 15% from the 1981 base values; although there was no accurate estimate for emissions from
this source or the capability to determine the major factors (i.e., domestic heating, forest fires,
etc.) contributing to PM from this category.
In 2002-2003, the LTADS (Lake Tahoe Atmospheric Deposition Study) collected and chemically
analyzed two-week integrated PM samples at locations throughout the basin (Dolislager et al.,
2009). Using the LTADS speciated chemical data, Kuhns et al. (2004) concluded 49% of the
elemental carbon was from wood smoke (a major contributor to visibility degradation) and
overall this source was responsible for 9% of the PM mass. This study also developed chemically
speciated wood smoke emissions profiles and a preliminary emissions inventory showing 32% of
the PM10 and 58% of the PM2.5 form wood smoke.
Gertler et al. (2008) prepared a more comprehensive and spatially distributed emissions
inventory. They attributed similar domestic heating (wood smoke) contributions to PM10 and
PM2.5. In addition, they reported wildfires resulted in 12% and 16% of the PM10 and PM2.5
emissions, respectively. More recently, Engelbrecht et al. (2009) performed a source
apportionment analysis of the LTADS dataset. As shown in Figure 1, wood smoke is a major
contributor to ambient PM2.5 levels; although there are significant seasonal differences. While
they were unable to separate contributions from the different sources of wood smoke, one can
infer form the seasonal differences that forest fires are the primary source during the summer and
domestic heating and prescribed fires dominated during the other periods.
Based on these studies, it is clear that wood smoke is a significant source of PM2.5 leading to
visibility degradation and environmental/health impacts in the basin. The results of the proposed
study would address a number of outstanding issues related to the contributions form specific
wood smoke sources and the seasonal dependence of emissions. Further, they would provide a
basis for validating the domestic heating vs. forest fire contributions reported in the emissions
inventory of Gertler et al. (2008).
A current project in the Lake Tahoe Basin entitled “Effects of burning in the Tahoe Basin on soil
and water quality” by Ken Hubbert and Co-PIs at the U.S. Forest Service is evaluating effects of
slash pile burning on soil physical, chemical, and biological properties. Collaboration and
coordination with this group will allow us to assess how various pile sizes, configuration, and
6
combustion properties (e.g., fire intensity as measured by underlying soil temperature) may
impact PM emissions and help to develop strategies to reduce impacts of prescribed fires on PMrelated air quality issues and deposition.
PM tracers for characterization of biomass combustion PM emissions: Molecular tracers that
reflect emissions from biomass burning include carbohydrates, carbohydrate anhydrides
(anhydrosugars), sugar alcohols, methoxyphenols, methoxy acids and resin acids (e.g., Feng
et al., 2007, Fine et al., 2004, Yttri et al., 2007; McDonald et al. 2000, Mazzoleni et al, 2007). A
commonly used tracer, levoglucosan (anhydrosugar), is a product of the thermal degradation of
cellulose and is frequently used in source apportionment studies to characterize biomass
combustion emission sources (e.g. Simoneit et al., 1999). Methoxylated phenols, guaiacols and
syringols, arising from pyrolysis of wood lignin are commonly found in biomass combustion
emissions (Hawthorne et al., 1988; McDonald et al., 2000). Resin acids include diterpenoids such
as pimaric, abietic and isopimaric acids and their thermal degradation product, dehydroabietic
acids. These compounds are important constituents of softwood resin and dehydroabietic acid
was proposed as a molecular tracer for coniferous wood combustion (Simoneit a et al, 1993). The
polar tracers have shown to comprise an important fraction of water soluble organic carbon in
atmospheric aerosols during winter months due to residential wood burning (Pashynska et al.,
2002, Puxbaum et al., 2007) as well as in emissions related to wildfires (Gao et al., 2003, Engling
et al., 2006, Mayol-Bracero et al., 2002). Reported concentrations of levoglucosan in atmospheric
aerosols vary dramatically ranging from lower ng m−3 levels at an oceanic background site
(Simoneit et al., 2004) to over 40 μg m−3 in wildfire smoke (Pashynska et al., 2002).
It has been recently reported (Medeiros and Simoneit, 2008) that burning of green vegetation
(simulated wildfires) release higher amounts of polar/water-soluble compounds such as unaltered
carbohydrates in comparison with dry/dead vegetation and residential wood combustion
emissions. Methyl-inositols seem to be more abundant in conifer green vegetation whereas
deoxy-inositols in oak vegetation. In addition, the most abundant lignin breakdown products
released from green vegetation burning are 4-hydroxyphenyl–type compounds such as pyrogallol,
4-hydroxybenzoic acid and shikimic acid (observed mostly in the conifer smoke extracts), and not
methoxyphenols, as reported for dry vegetation burning. Thus, these organic markers have a
potential to differentiate between emissions from wildland fires and residential wood combustion.
Figure 2 and associated table shows an example of one of the proposed organic compounds and a
list the species we propose to analyze for this study.
Other tracers for biomass combustion includes soluble K+ content in fine aerosols, although this
element is not a unique in biomass smoke and also found in other combustion emissions (e.g.,
Schauer et a. 1999). Levoglucosan have even been used in sediment cores and soils to determine
historic and pale-fire emissions and inputs (e.g., Elias et al., 2001, Kuo et al., 2008). However,
because these tracers are water-soluble, they may be prone to post-depositional processes, and are
generally used in soils and sediments as qualitative rather than quantitative tracer. Particulatebound Hg, on the other hand, is insoluble in water and this signature may potentially also be used
for characterization of past fire histories in sediment and soil reservoirs. If the characterization of
PM emission sources using this novel approach proves to be successful, we will pursue funding to
use this tracer approach in sediments and soils for reconstruction of historic occurrence of
wildfires in the Lake Tahoe basin.
Particulate-bound Hg as a novel biomass combustion tracer: Hg emissions from wildfires are
known to be a major natural source of Hg to the atmosphere contributing to both regional
pollution and the global atmospheric Hg pool (Artaxo et al., 2000, Brunke et al., 2001, Obrist et
al., 2007). Wild-fire related Hg emissions are due to the fact that Hg contained in biomass and
organic carbon pools almost completely emit during biomass burning. Emissions can occur in
two forms: gaseous elemental Hg and particulate-bound Hg (Friedli et al. 2003). Obrist et al.,
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(2007) recently characterized chemical signatures of Hg in biomass smoke emissions under
controlled conditions in different fuel types, including fresh and air-dried leaves, needles, and
woody branches. Their results showed that (i) Hg contents in emissions directly relate to the
original fueld Hg contents; (ii) very substantial amounts of particulate-bound Hg were found in
aerosols of fresh fuels (e.g., leaves, fresh branches) while dry fuel emissions showed no
particulate-bound Hg levels because Hg was lost in gaseous form. The authors concluded that
particulate-bound emissions are highly fuel-specific depending on combustion properties (i.e.,
flaming versus smoldering combustion) and fuel type.
Obrist et al. (2009) also characterized Hg concentration in main fuel types of four Sierra Nevada
forest sites as part of a project to develop a first national database on Hg concentrations and pools
associated with US forest ecosystems (US EPA STAR Grant # R833378). Two of their sites are
located near Truckee, CA (“Truckee sites”) and two sites are located on the east slope of the
Carson range immediately outside of the Lake Tahoe basin (“Little Valley”). The study showed
very distinct differences in fuel Hg concentrations (Figure 3): Hg concentrations of the main tree
(mainly Jeffrey Pine) and shrub species of the four sites showed considerable Hg levels (15 to 60
μg kg-1) with lower concentrations in understory vegetation. Other above-ground biomass tissues
such as branches and bark also showed significant Hg concentrations (12 – 21 μg kg-1), and
highest Hg levels were observed in surface litter horizons reaching up to 134 μg kg-1. However,
bole wood concentrations were extremely low across all sites ranging from barely above the
detection limit of the analyzer (~0.2 μg kg-1) to below detection limits.
Based on these inventories and Hg emissions observed in previous studies, we can expect very
pronounced differences in particulate-phase Hg emissions during combustion of domestic wood
fuels—i.e., mainly logs of bole wood—and combustion of other fuel components such as
understory vegetation, tree bark, and organic surface litter horizons. In addition, effects of fuel
moisture and fire intensity lead to further differences in particulate-phase Hg loadings. Wildfires
and ground-fires often show distinct smoldering-phase combustion (Andreae and Merlet, 2001,
Chen et al., 2007) while domestic wood combustions are dominated by high-intensity flaming
combustion. Preliminary observations in the field indicate highly variable particulate-phase Hg
loadings in emission plumes which are related to different fire types (Finley et al., 2009), but no
systematic investigation have confirmed this yet.
G. Strategy for Engaging with Managers and Obtaining Permits
Relevant stakeholders in the Lake Tahoe Basin will be engaged throughout the research project
and the lead scientists will present the findings to representatives of management agencies in the
Basin to aid with integrating the research outputs with future management options. This will be
accomplished through the COS (Committee of Scientists, Alan Gertler is a member of this
group), presentations at appropriate venues (e.g., the Tahoe Basin Science Conference and annual
Lake Tahoe Forum), and articles in the TSC (Tahoe Science Consortium) newsletter.
Collaboration with agencies and existing projects (e.g., Matt Busse, U.S. Forest Service) will
allow coordination of activities in regards to prescribe fire activities
H. Description of Deliverables/Products
Products of this project includes a comprehensive data set on PM2.5 tracer signatures (K+,
levoglucosan, Hg) for biomass combustion PM emission from domestic wood combustion,
prescribed fire activities, and natural wildfires. These tracers will be specific to specific the Lake
Tahoe basin as all investigation will occur within or in close proximity to the basin; however,
they may also be applied and validated as tracers in other sites. Future use of the proposed tracer
signatures may include application for sediment and soil to reconstruct past fire history in the
Lake Tahoe Basin.
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III. Schedule of Major Milestones/Deliverables
Milestone/Deliverables
Project Start
Start Date
May 2010
Filter Collection:
Wildfires
End Date
Description
June 2010
September 2010
June 2011*
September 2011*
Filter collection:
Prescribed fires
October 2010
December 2010
Filter collection for PM
emission from prescribed
fires; depending on
prescribed burning activities
and in coordination with
agencies and research group
Hubbert et al.
Filter collection:
Domestic wood
combustion
November 2010
March 2011
Filter collection in areas
affected by domestic wood
combustion.
Filter Analysis
February 2011
November 2011
Data Analysis,
presenatins, publications
Throughout study period
(i.e., March 2010 to February 2012)
Project end
Filter collection natural in
wildfire emission plumes.
Due to the unpredictable
nature of wildfires,
alternative “back-up” dates
(marked as *) for filter
collection from wildfires will
be June to September 2011.
Detailed chemical
characterization of PM
(mass, organics, Hg, K+)
Data analysis, presentations
at conferences and to
stakeholders, writing of
articles, progress reports,
final reports, and peerreviewed article
February 2012
List of Detailed Deliverables:
•
•
•
•
Yearly progress report and comprehensive final report on field sampling activities,
analytical results, and data analysis of the project to the project sponsor.
At least one conference presentation per year at appropriate venues (e.g., the Tahoe Basin
Science Conference and annual Lake Tahoe Forum).
At least one article per year in the TSC (Tahoe Science Consortium) newsletter .
At least one peer-review journal article in an international journal (e.g., Environmental
Science and Technology).
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IV. Literature Cited
Andreae MO, Merlet P (2001) Emission of trace gases and aerosols from biomass burning. Global
Biogeochem. Cycles, 15, 955–966.
Artaxo P, Calixto de Campos R, Fernandes ET, Martins JV, Xiao Z, Lindqvist O, Fernández-Jiménez MT,
Maenhaut W (2000) Large scale mercury and trace element measurements in the Amazon basin.
Atmos. Environ., 34, 4085–4096.
Brunke E-G, Labuschagne C, Slemr F (2000) Gaseous mercury emissions from a fire in the Cape
Peninsula, South Africa, during January. Geophys. Res. Lett. 2001, 28, 1483–1486.
Chang M-C, Chow JC, Kohl S, Voepel H, (2005) Sampling and analysis or the Lake Tahoe atmospheric
deposition study. Desert Research Institute.
Chen L-W A, Moosmüller H, Arnott WP, Chow JC, Watson JG (2007) Particle emissions from laboratory
combustion of wildland fuels: Emission factors and source profiles. Environ. Sci. Technol. 41, 4317–
4325.
Cliff SS, Cahill TA (2000). Air Quality. Chapter 3. in: Murphy, D.D.; Knopp, C.M., eds. Lake Tahoe
watershed assessment: Volume I. Gen. Tech. Rep. PSW-GTR-175. Albany, CA: U.S. Department of
Agriculture, Forest Service, Pacific Southwest Research Station. 736p.
Dolislager LJ, VanCuren R, Pederson JR, Lashgari A, McCauley E (2009). A summary of the lake tahoe
atmospheric deposition study (LTADS), Atmospheric Environment, in press.
Elias BRT, Simoneit RC, Cordeiro, Turcq B (2001) Evaluating levoglucosan as an indicator of biomass
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V. Figures
Figure 1:
Sandy Way, Two-week Samplers, CMB Source Attribution
PM2.5, PMCoarse, & PM10
35
Concentration, μg/m3
30
25
20
Unknown
Sec Amm Nit
Sec Amm Sulf
Vegetative Burn
Diesel
Gasoline
Roadsalt
Geol 2
Geol 1
15
10
5
Fa
ll0
2P
W
M
in
C
te
rs
r0
3P
Sp
M
rin
C
rs
g0
Su
3P
m
M
m
C
er
rs
03
PM
C
Fa
rs
ll0
3P
W
M
in
C
te
rs
r0
4P
M
C
rs
Fa
ll0
2P
W
M
in
10
te
C
r0
lc
3P
Sp
M
rin
10
g0
C
lc
Su
3P
m
M
m
10
er
C
03
lc
PM
Fa
10
C
ll0
lc
3P
W
M
in
10
te
r0
C
lc
4P
M
10
C
lc
Fa
ll0
2P
W
M
in
2.
te
5
r0
3P
Sp
M
rin
2.
5
g0
Su
3P
m
M
m
2.
er
5
03
PM
Fa
2.
5
ll0
3P
W
M
in
2.
te
5
r0
4P
M
2.
5
0
Season, Year, Size fraction
Figure 1. Two week samplers, Sandy Way site: Summary of seasonal average CMB modeled
source contributions for measured PM2.5, PMCoarse, and calculated PM10 (Engelbrecht et al., 2009)
12
Figure 2:
Carbohydrates
Anhydrosugars
Lignin derivatives
Diterpenoids
Arabitol
Levoglucosan
Pyrogallol
Dehydroabietic acid
Methyl-inositols
Mannosan
4-Hydroxybenzoic acid
Abietic acid
Shikimic acid
Pimaric acid
Deoxy-inositols
Figure 2: Arabitol, one of the carbohydrates proposed for differentiation of various biomass
combustion sources for PM loads in Lake Tahoe basin and list of proposed organic substances for
this study.
13
Figure 3:
Figure 3. Total biomass mercury contents (in μg kg-1 dry mass) in four Pine forest sites nearby
Lake Tahoe (modified from Obrist et al., 2009). Data show significant mercury contents in most
above-ground carbon pools with the exception of bole wood which show very low mercury levels
often below detection limits (< d.l.) of the analyzer.
14