Proposal: Tahoe Research Supported by SNPLMA Round 10 I. Title Page Title: Visibility Monitoring and Standards for Lake Tahoe Basin: Assessment of Current and Alternative Approaches Subtheme this proposal is responding to Theme: Air Quality and Meteorology Subtheme: Impact and control of atmospheric particulate matter Principal Investigator and Receiving Institution L.-W. Antony Chen, Ph.D. Division of Atmospheric Sciences Desert Research Institute 2215 Raggio Parkway Reno, NV 89512 Phone: 775-674-7028 Fax: 775-674-7009 Email: antony@dri.edu John, G. Watson, Ph.D. Division of Atmospheric Sciences Desert Research Institute 2215 Raggio Parkway Reno, NV 89512 Phone: 775-674-7046 Fax: 775-674-7009 Email: johnw@dri.edu Co-Principal Investigator Agency Collaborator Grants Contact Person Funding requested: Total cost share (value of financial and in-kind contributions): Xiaoliaong, Wang, Ph.D. Division of Atmospheric Sciences Desert Research Institute 2215 Raggio Parkway Reno, NV 89512 Phone: 775-674-7177 Fax: 775-674-7009 Email: xiaoliang.wang@dri.edu N/A Lycia Ronchetti Business Manager Division of Atmospheric Sciences Desert Research Institute 2215 Raggio Parkway Reno, NV 89512 Phone: 775-673-7411 Fax: 775-674-7016 Email: Lycia.Ronchetti@dri.edu $ 49,181 1 Proposal: Tahoe Research Supported by SNPLMA Round 10 II. Proposal Narrative a. Project abstract Visibility is an important asset of the Lake Tahoe Basin and has been routinely monitored since 1989. Despite appreciable improvements recorded in the sub-regional visibility, today the monitoring program is facing challenges including its accuracy, spatial and temporal coverage, and cost. In addition, the current visibility standards to be met or exceeded differ from US Environmental Protection Agency (U.S.EPA) guidance for mandatory Class I areas. This project will evaluate current visibility measurements and indicators available for tracking haze in the Lake Tahoe Basin and the nearby Desolation Wilderness, which is a mandatory Class I areas. The project will provide recommendations for future monitoring, data analysis, and threshold development. The project consists four tasks: 1) Critical review of guidance documents and previous studies; 2) Compilation of relevant visibility and particulate matter databases; 3) Examination of alternative monitoring technologies; and 4) Synthesis, reporting, and recommendations. The project will be completed within 12 months. Alternatives to current measurement methods and indicators may include remote sensing and/or satellite measurements. Findings and recommendations will be communicated to key stakeholders concerned with reducing the effects of airborne particles on visibility and water clarity. b. Justification statement Lake Tahoe is a unique environmental asset that has been designated an “Outstanding National Water Resource” by the U.S.EPA to protect its water quality and scenic characteristics. Of particular concern is the deterioration of optical clarity of Lake Tahoe’s water owing to algal growth nourished by excess nutrient inputs and atmospheric deposition of fine particle matter (PM) (Goldman and Byron, 1986; Jassby et al., 1999). Atmospheric PM also degrades visibility (e.g., Chen et al., 2003), another air quality related value for residents and visitors. The 1999 Regional Haze Rule (U.S.EPA, 1999a), later renamed the Clean Air Visibility Rule (CAVR, see U.S.EPA, 2005), that implements Section 169B of the Clean Air Act (CAA) seeks to return 156 national parks and wilderness areas to their “natural” visibility conditions by 2065. Several guidance documents relevant to the requirements of the Regional Haze Rule have been established (e.g., Watson, 2002). Most important is the guidance for estimating the highest and lowest 20th percentiles of light extinction and the natural visibility levels for the Class I areas. The Lake Tahoe Basin contains one of the Class I areas, the Desolation Wilderness, and two visibility monitoring sites have been operated since 1990 to evaluate this important resource on a regional and sub-regional scale. Visibility standards and goals have been developed by the Tahoe Regional Planning Agency (TRPA). However, little is known about the adequacy of the current monitoring program with respect to accuracy, spatial and temporal representativeness, and source attribution of optical extinction and fine PM mass. Moreover, since the TRPA standards differ from those for the Class I areas (see Section c), it is necessary to evaluate their effectiveness for regional air quality planning. This project responds to the Air Quality Subtheme 3a: Impact and control of atmospheric particulate matter, particularly focus 5) “Prepare a monitoring plan and develop new indicators of regional and sub-regional visibility in the Basin in accordance with U.S.EPA guidance”. It will evaluate the current visibility measurements and indicators available for tracking haze in the Lake Tahoe Basin and provide recommendations for future monitoring, data analysis, and threshold development. The technical approach includes examining visibility trends derived from TRPA monitoring sites and comparing them with those from nearby regional haze sites and other measures of haze (e.g., California and Nevada PM sites, National Weather Service (NWS) airport visibility, satellite aerosol optical depth, etc.). Previous visibility and PM2.5 (PM with aerodynamic diameter equal or less than 2.5 m) studies in this region, especially those funded by SNPLMA will be critically reviewed. Recently-developed monitors, such as portable filter samplers, nephelometers, optical particle sizers, and aethalometers, that 2 Proposal: Tahoe Research Supported by SNPLMA Round 10 address local and regional hazes will be explored with respect to their ability to continuously measure haze, track long-term trends, identify sources, and separate local from regional contributions. Alternatives to current monitoring methods will be evaluated with respect to continuity with the current visibility record, initial costs, and operating costs. c. Concise background and problem statement TRPA has operated visibility monitoring sites at the South Shore co-located with the Lake Tahoe Boulevard station and at Bliss State Park on the West Shore to represent sub-regional (urban) and regional visibility, respectively. As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, these sites contained a Optec NGN-2 ambient nephelometer for light scattering at ~530 nm, IMPROVE aerosol samplers for PM2.5 mass, elements, ions, and carbon, and for PM10 mass, and meteorological stations for wind speed, wind direction, temperature, and relative humidity. The South Shore site (SOLA1) became operational in 1989, and the Bliss State Park site (BLIS1) became operational in 1990. IMPROVE took over operation of the BLIS1 site in 1999. Aerosol chemical concentrations are available from the IMPROVE Visibility Information Exchange Web System (VIEWS: http://views.cira.colostate.edu/web/) from 1991 – 1996 for SOLA1 and from 1991 – 2007 for BLIS1 (measurements were continuously made at SOLA1 after 1996 until 2004 but not reported to VIEWS). According to the Draft Guidance for Tracking Progress under the 1999 Regional Haze Rule (U.S.EPA, 2001b), haze is expressed in deciviews (dv) derived from the light from extinction coefficient (bext) determined by a chemical extinction budget that includes clear air scattering of 10 Mm–1 plus a weighted sum of the ammonium sulfate [(NH4)2SO4], ammonium nitrate (NH4NO3), organic material (OM), soot (EC) (or light absorbing carbon [LAC], fine geological material (soil), and coarse mass (assuming it is present entirely as geological material) measured on 24-hr filter samples taken in or near Class I areas (Malm et al., 1994): bext = 10 + 3f(RH)×[(NH4)2SO4 + NH4NO3] + 4×[OM] + 10×[EC] + 1×[fine soil] + 0.6×[coarse mass] (1) where f(RH) is the extinction growth factor for (NH4)2SO4 and NH4NO3 with increasing relative humidity (RH) (Tang, 1996 and references therein). Eq. 1 was revisited and refined lately (Pitchford et al., 2007). Figure 1 shows bext trends at SOLA1 and BLIS1 since their inception. There was a substantial improvement of visibility at SOLA1 between 1991 and 1996 as bext decreased by ~50%. bext has remained more of a constant since 1996 (not shown). At BLIS1, the highest bext was recorded in 2007, indicating a level or increasing trend. Emission reductions, especially from vehicle exhaust and residential wood combustion, within Basin can explain improvements in the sub-regional visibility. Regional visibility is more influenced by out-of-basin sources (Gertler et al., 2006), for which emission trends are less identifiable. TRPA uses 1991–1993 monitoring data (chemical bext) at each monitor as the maximum allowable (3-year average) at that monitor (TRPA, 2007). It has been proposed to replace the 1991–1993 values with the 2001–2003 values, which would be lower than 25 Mm-1/34 Mm-1 at least 50/90 percent of the time at BLIS1 and 50 Mm-1/125 Mm-1 at least 50/90 percent of the time at SOLA1. Regional visibility (at BLIS1) appears to exceed these limits in 2007. However, it is the 20% best and 20% worst which matters under the regional haze rule, not annual averages as shown in Figure 1. For state visibility standards, visual range is calculated from nephelometer data collected at Bliss State Park and Lake Tahoe Boulevard for periods during which RH is <70%. Previous data analyses show that light scattering (bscat) by nephelometer underestimates chemical bext (Eq. 1) by 35%. It also underestimates bext from chemical size distributions measured with micro-orifice uniform deposit impactor (MOUDI) and cascade impactors by 25% (Watson et al., 2008). bext contains a light absorbing component (babs) which is not measured by nephelometer. babs is important for aerosols influenced by combustion sources such as wildfires, prescribed burns, residential wood combustion, and diesel engine exhaust (Chen et al., 2006). 3 Proposal: Tahoe Research Supported by SNPLMA Round 10 180 Chemical bext (Mm-1) 160 y = -14.6x + 29324.8 140 SOLA1 BLIS1 120 100 80 60 y = 0.2x - 387.9 40 20 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 Year Figure 1. Trend of bext at SOLA1 and BLIS1 based on annual averages. The shaded area indicates the TRPA baseline period. Measurements were continuously made at SOLA1 after 1996 but not reported to VIEWS. Several issues need to be addressed in evaluating Lake Tahoe visibility metrics: i) Assumptions concerning the chemical extinction budget on which the Eq. 1 is based experience deviations from sample to sample (Watson, 2002). The effects of these deviations on decisionmaking must be evaluated in relation to the ability of the tracking methodology to detect average changes over long time periods rather than for their absolute accuracy on a specific sample. ii) Wood smoke and engine exhaust generate aerosols that are highly light absorbing. Nephelometers likely underestimate bext caused by these aerosols. This affects the compliance with state visibility regulations. iii) Zones of representation of the two monitoring sites are not well assessed. Because of the complex terrain, scattered local sources, and inhomogeneous events such as wildland fires in the basin, the PM and visibility may experience substantial non-uniformity that limits the zone the two sites can represent. iv) As stated in TRPA (2007), “TRPA continues to be concerned that due to the tremendous variability in visibility and the limited number of days sampled for regional visibility, the attainment status could change if additional sample days are used”. The 1-in-3- and 1-in-6-day sampling schedules were found adequate in some studies (Chow et al., 2005), but insufficient in other studies. Daytime visibility is most important, even though some of the highest concentrations might occur at might. The current 24-hr samples do not address diurnal variations. v) Also stated in TRPA (2007), “Due to the significant improvements made on the threshold, the TRPA redirected resources to other areas within air quality and has temporarily suspended the collection and analysis of the visibility data”. The effects of this break in the trendline should be assessed. vi) Considering the improvement of visibility (at least the sub-regional visibility) in the basin since the 1990’s, an Air Quality Threshold alternative should be analyzed to set a higher bar as a goal for attainment than maintenance of the 1991–1993 levels. Such an analysis needs be based on solid scientific evidence. d. Goals, objectives, and hypotheses to be tested The goal of the project is to evaluate the current visibility measurements and indicators available (not limited to the TRPA sites) for tracking haze in the Lake Tahoe Basin and provide recommendations for future monitoring, data analysis, and threshold development. 4 Proposal: Tahoe Research Supported by SNPLMA Round 10 Based on critical reviews of available data and literature, the project seeks to address each of the issues listed in Section c. Major hypotheses to be tested are A. There is consistency between optical and chemical scattering coefficients (bscat), and when aerosol light absorption is included (e.g., from densitometer measurement of Teflon filter opacity), optical bext agrees with the chemical bext. B. The BLIS1 site, after removing short-term events (i.e., local influences), represents regional haze since it is generally remote from source areas. SOLA1 PM and visibility have been approaching this level since 1991. C. Annual or 3-year averages for PM and bext are reasonably consistent for sampling frequencies of 1-in-6 days and 1-in-12 days, but at least for the sub-regional SOLA1 site, the maximum and second-highest concentrations are sensitive to sampling frequency regardless of lag time between samples. D. Alterative visibility measurement systems sensors can reduce initial and operating costs. E. Space-based satellite data, particularly Moderate Resolution Imaging Spectroradiometer (MODIS) products, can supplement, and under some circumstances replace, ground-based visibility monitoring, due to their nearly-continuous spatial and twice-daily temporal coverage. F. TRPA visibility standards are comparable to those for manadory Class I areas, except that U.S.EPA requires an always declining level of bext until natural background. G. Source apportionment for bext through multivariate and chemical mass balance (CMB) analysis of available PM data agrees with emission inventories and air quality models applicable to the Lake Tahoe region. e. Approach, methodology and location of research This project consists four tasks to be accomplished from 05/01/2010 to 04/30/2011: Task 1: Critically review guidance documents and previous studies: As reviewed by Watson (2002), Guidance relevant to Regional Haze Rule implementation includes: Guidance for Demonstrating Attainment of Air Quality Goals for PM2.5 and Regional Haze (U.S.EPA, 2001a) Tracking Process under the Regional Haze Rule (U.S.EPA, 2001b) Guidance for Estimating Natural Visibility Conditions under the Regional Haze Rule (U.S.EPA, 2001c) Emission Inventory Guidance for Implementation of Ozone and PM NAAQS and Regional Haze Regulations (U.S.EPA, 1999b) Federal Land Managers’ Air Quality-Related Values Workshop (FLAG, 2000) State of California Regional Haze State Implementation Plan (SIP). Revisions to these documents after Watson (2002) will be summarized and their relevance to Lake Tahoe visibility monitoring will be tabulated. Visibility and PM studies, both observational and modeling (e.g., Cahill et al., 1977; Pitchford and Allison, 1984; Molenar et al., 1994; Tarnay et al., 2001; VanCuren and Cahill, 2002; Kuhns et al., 2004; Chang et al., 2005; Gertler et al., 2006; Dolislager et al., 2009) will be reviewed with their major findings documented. This task directly addresses hypotheses (F) and (G) and forms basis for testing other hypotheses. 5 Proposal: Tahoe Research Supported by SNPLMA Round 10 Task 2: Obtain, format, document, and evaluate visibility and PM databases TRPA, Air Resource Specialists, Inc. (ARS), and other agencies (e.g., Cooperative Institute for Research in the Atmosphere [CIRA], U.S.EPA, California Air Resource Board [CARB], and Nevada Bureau of Air Quality Planning [NBAQP]) will be contacted to obtain visibility-related data from Lake Tahoe and nearby monitoring sites. TRPA contracted with ARS since 1989 to operate the visibility program. CIRA has been responsible for archiving the IMPROVE network data, while USPEA maintains air quality databases (i.e., U.S.EPA Air Quality System database [AQS]: http://www.epa.gov/ttn/airs/airsaqs/index.htm) for the Chemical Speciation Network (CSN). CARB acquires continuous PM10 data from the South Lake Tahoe-Sandy Way site and NBAQP monitors PM2.5 continuously at nearly Carson City and Aspen Park. In addition, visibility is reported (in miles, based on first principle measurement) by NWS for the South Lake Tahoe Airport. The obtained data will be unified into a Microsoft ACCESS database. This will include data tables for: 1) variable names, mnemonics, and units; 2) site codes, names, coordinates, and descriptions; and 3) ambient concentrations. These will be linked by common keys such as sampling time. Queries will be developed to segregate data into different seasons and to transform the data into format needed for intercomparisons. Continuous meteorological data will be obtained from NWS, CARB, and CIRA and synchronized with the PM and visibility data in the database to facilitate time series analysis. Optical babs (filter transmittance) measurements are available for all IMPROVE samples, and along with the nephelometer data, optical bext can be determined. The optical and chemical bscat and bext will be compared for different seasons and ambient conditions (temperature, RH, etc.). This will address hypothesis (A). Nephelometer data will also be used to examine the effect of sample durations and frequencies on annual visibility averages (i.e., hypothesis [C]). Twenty-four-hour averages of bscat will be calculated for each sampling day. The annual average and standard deviation, highest, second-highest, and several upper percentiles of the 24-hour bscat will be compared for samples taken at daily and two-, three-, six-, 12-, and 30-day intervals. Same will be done for PM data acquired at three- (only BLIS1), six-, 12-, and 30-day intervals. Inter-site comparisons and wind analysis will bound the source region of PM and bext, and therefore address hypothesis (B). Watson and Chow (2001) demonstrated a successive moving average subtraction method that used 5-min bscat measurements to detect short-term spikes of nearby small emitters and sites located within the urban/regional plume, but distant from specific emitters (Figure 2). This method will examine the extent to which BLIS1 and SOLA1 represent regional and subregional sites. MODIS satellite data should also help assess the zone of representation of each site (see Task 3). 12/28/00 (Thursday) 1200 -1 -1 bscat (Mm Bsp (Mm ) ) 1000 FSF ANGI FSF baseline ANGI baseline 800 600 400 200 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Hour (PST) Figure 2. Example of baselines at Fresno, CA and Angiola, CA sites with the 5-min average bscat on 12/28/00 (Thursday), using 15-min moving average. Task 3: Examine alternative monitoring technologies 6 Proposal: Tahoe Research Supported by SNPLMA Round 10 Chow et al. (2008) reviewed integrated and continuous measurements for particle mass and chemical composition, and this is a starting point for identifying and evaluating alternative visibility monitoring technology. A nephelometer usually costs >$10,000, and even the simplified versions such as DustTrak® (TSI, Inc., Shoreview, MN) and Belfort model 6220 forward scatter visibility meter used by NWS Automated Surface Observing System (ASOS) cost several thousand dollars. Considering the challenge of spatial variability and funding limitation for the Tahoe visibility monitoring program, it is reasonable to deploy a monitoring network that consists of small, inexpensive sensors. An example of such sensor is the particle monitor developed at the University of California, Berkeley (UCB) (Litton et al., 2004; Chowdhury et al., 2007; Edwards et al., 2006). The UCB monitor is modified from a commercial household smoke detector (First Alert SA302, $25) that combines ionization chamber sensing (ion depletion by airborne particles) and photoelectric sensing (optical scattering by airborne particles). With longer averaging time and modifications of the light source and photodetector, the lower detection limit can be significantly reduced. Laboratory (Edwards et al., 2006) and field (Chowdhury et al., 2007) measurements showed reasonable correlation between the UCB monitor signal and PM2.5 mass concentration. Such an inexpensive device shows promise of wide deployment to monitor the spatial and temporal change of visibility. Remote sensing represents another potential direction, and such techniques have been deployed by NASA’s AErosol RObotic NETwork (AERONET). AERONET is an optical ground-based aerosol monitoring network (Holben et al., 1998) that uses sun-sky scanning photometers to provide quality assured aerosol optical properties integrated through the Earth’s atmosphere. AERONET’s automatic tracking photometer measures direct sun irradiance within a 1.2 field of view at least every 15 min at 340, 380, 440, 500, 675, 870, and 1020 nm to obtain spectral aerosol optical depth (AOD). Six sky radiance scans are made daily at solar zenith angles of ~75.5, 70.5, and 60 both morning and afternoon. Algorithms were developed (Dubovik and King, 2000) to retrieve single scatter albedo (), scattering phase function f[], as well as aerosol volume-size distribution and complex refractive index. AOD is a measure of column-integrated bext, while determines the fraction of extinction due to scattering (i.e., bscat/bext) and f[] estimates the fraction of forward- and back-scattering. Although AERONET is not looking at the surface, surface haze often dominates AOD. Owing to the nature of spatial averaging, AOD may be a better indicator of regional haze than bext measured at a single point. In recent years, advanced satellite remote sensing techniques have been developed by NASA and NOAA to measure the column-integrated aerosol optical properties from space, which enables the quantification of spatial and temporal distribution of aerosols on an urban to global scale (Hidy et al., 2009). MODIS aboard the Terra and Aqua satellites is one of the major satellite remote sensors used for AOD retrieval (Kaufman and Fraser, 1997; Tanre et al., 2001). Terra MODIS and Aqua MODIS view the entire Earth’s surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths. Aerosol size distributions are derived over the oceans, and the aerosol type is derived over the continents. Daily Level 2 (MOD 04) data are produced at the spatial resolution of a 10×10-km (at nadir) pixel array. Green et al. (2009) showed good agreements between MODIS and AERONET AOD and IMPROVE PM2.5 mass at Bondville, IL. On clear days, MODIS AOD should be valuable for assessing visibility in the Lake Tahoe region. MODIS data will be downloaded (http://modis.gsfc.nasa.gov/data/) and compared with the surface measurements. Other direct and remote sensing techniques will be explored to address hypotheses (D) and (E). Most of these techniques, however, do not yield speciation of aerosol, as the IMPROVE network does. Nevertheless, some particle characteristics (e.g., size distribution, signal scattering albedo, and refractive index) can be derived from the measurements if certain assumptions are met. The chemical speciation provides the opportunity to examine sources (e.g., Chen et al., 2002; 2007), and the source information is necessary to help determine the appropriate control. Task 4: Synthesis, reporting, and recommendations 7 Proposal: Tahoe Research Supported by SNPLMA Round 10 This task will 1) evaluate the current visibility standards and 2) recommend monitoring strategies for different resource levels. The recommendations will be based on most recent U.S.EPA guidance documents, complemented by information synthesized from the first three tasks, as part of the final report. The final report will include all background information and the visibility databases. f. Relationship of the research to previous and current relevant research, monitoring, and/or environmental improvement efforts The last comprehensive Lake Tahoe visibility study was published in 1984 (Pitchford and Allison, 1984). The proposed study is considered necessary in terms of understanding what we are currently at and planning for the future. It will also examine how the current threshold compare to those for Class I areas (i.e, the IMPROVE network), and therefore will guide us to achieve a national goal of returning visibility to its “natural” condition by 2065. The project complements intensive PM monitoring and source apportionment studies conducted in Lake Tahoe. This includes Lake Tahoe Atmospheric Deposition Study (LTADS, see Chang et al., 2005 and Dolislager et al., 2009), which resolved a seasonal variation of PM2.5 and PM10 owing to increased traffic, sanding, and wood burning activities in winter, and Tahoe Source Characterization Study (TSCS, see Kuhns et al., 2004), which, based on emission estimates, indicated that residential wood combustion, unpaved road dust, and paved road dust are the largest PM sources in the basin. The SNPLMA Round 7 also sponsored a project (PI. Johann Engelbrecht) to perform multivariate source apportionment using the LTADS monitoring data. g. Strategy for engaging with managers and obtaining permits As mentioned in Task 2, Section e, the project team will coordinate with several agencies to obtain visibility and PM monitoring data as well as satellite data. Ideas and findings will be circulated for feedback and comments. In order to ensure effective use of the monitoring plans developed as part of this study, presentations will be made to key stakeholders interested in Lake Tahoe visibility issues. On-going progress and results will be presented to the Tahoe Science Consortium, TSC, following its full implementation, EPA Region 9, TRPA, CARB, Lahontan, NDEP, UC Davis, UNR, Caltrans, and NDOT. Our assessments will be presented at the annual Tahoe Science Symposium to maximize communication and information dissemination. DRI will also work with these groups and other interested parties to apply the results of work to evaluate and develop strategies to monitor visibility for compliance in the basin. Scientific publications in peer-reviewed journals will result from this project. h. Description of deliverables/products and plan for how data and products will be reviewed and made available to end users Deliverables will consist of: 1) interim submittal; 2) draft report; 3) presentation of findings; and 4) final report. An interim submittal will be delivered to TSC and TRPA 6 months after the contract starts. This submittal will contain a visibility-related database and descriptions for the sources of data. The draft report documenting the literature review, data analysis, method evaluation, and conclusions/ recommendations will be completed 10 months after the contract is in place. This report will address hypotheses identified in Section d of this proposal. Presentation of findings will be made at DRI and TSC conferences (if possible). Comments and suggestions on the draft report and presentation will be incorporated into the final report, which will be delivered 1 month after the project period. Progress will be tracked through regular e-mails and conference calls with the program manager(s). Research results will also be published in peer-reviewed journals and/or professional magazines, and made available through the internet. 8 Proposal: Tahoe Research Supported by SNPLMA Round 10 III. Schedule of major milestones/deliverables Milestone/Deliverables Prepare progress reports Interim submittals (visibility/PM databases) Draft Report Final Report Start Date End Date Description 5/1/2010 4/31/2011 Submit brief progress report to Tahoe Science Program coordinator by the 1st of July, October, January, and April. Prepare summary of annual accomplishments in January. 5/1/2010 10/31/2010 Visibility-related database and descriptions for the sources of data will be delivered to TRPA and TSC. 11/1/2010 2/28/2011 Draft report submitted to Tahoe Science Program coordinator and TRPA. 3/1/2011 4/30/2011 Final report submitted to Tahoe Science Program coordinator and TRPA. 9 Proposal: Tahoe Research Supported by SNPLMA Round 10 IV. Literature Cited Cahill, T.A.; Ashbaugh, L.L.; Barone, J.B. (1977). Sources of Visibility Degredation (sic) in the Lake Tahoe Air Basin. Report Number TD 883.5.C2C35c.2; prepared by University of California, Davis, Davis, CA, for California Air Resource Board. Chang, M.-C.O.; Chow, J.C.; Kohl, S.D.; Voepel, H.; Watson, J.G. (2005). Sampling and analysis for the Lake Tahoe atmospheric deposition study. prepared by Desert Research Institute, Reno, NV, for California Air Resources Board, Sacramento, CA. Chen, L.-W.A.; Doddridge, B.G.; Chow, J.C.; Dickerson, R.R.; Ryan, W.F.; Mueller, P.K. (2003). Analysis of summertime PM2.5 and haze episode in the mid-Atlantic region. J. Air Waste Manage. Assoc., 53(8): 946956. Chen, L.-W.A.; Doddridge, B.G.; Dickerson, R.R.; Chow, J.C.; Henry, R.C. (2002). Origins of fine aerosol mass in the Baltimore-Washington corridor: Implications from observation, factor analysis, and ensemble air parcel back trajectories. Atmos. Environ., 36(28): 4541-4554. Chen, L.-W.A.; Moosmüller, H.; Arnott, W.P.; Chow, J.C.; Watson, J.G.; Susott, R.A.; Babbitt, R.E.; Wold, C.; Lincoln, E.; Hao, W.M. (2006). Particle emissions from laboratory combustion of wildland fuels: In situ optical and mass measurements. Geophys. Res. Lett., 33(L04803): 1-4. doi:10.1029/2005GL024838. Chen, L.-W.A.; Watson, J.G.; Chow, J.C.; Magliano, K.L. (2007). Quantifying PM2.5 source contributions for the San Joaquin Valley with multivariate receptor models. Environ. Sci. Technol., 41(8): 2818-2826. Chow, J.C.; Chen, L.-W.A.; Lowenthal, D.H.; Doraiswamy, P.; Park, K.; Kohl, S.D.; Trimble, D.L.; Watson, J.G. (2005). California Regional PM10/PM2.5 Air Quality Study (CRPAQS) - Initial data analysis of field program measurements. Report Number 2497; prepared by Desert Research Institute, Reno, NV, for California Air Resources Board, Sacramento, CA. Chow, J.C.; Watson, J.G.; Lowenthal, D.H.; Park, K.; Doraiswamy, P.; Bowers, K.; Bode, R. (2008). Continuous and filter-based measurements of PM2.5 nitrate and sulfate at the Fresno Supersite. Environ. Mon. Assess., 144(1-3): 179-189. Chowdhury, Z.; Edwards, R.D.; Johnson, M.; Shields, K.N.; Allen, T.; Canuz, E.; Smith, K.R. (2007). Journal of Environmental Monitoring 9(10): 1099-1106. Dolislager, L.J.; VanCuren, R.A.; Pederson, J.R.; Lashgari, A.; McCauley, E. (2009). A summary of the lake tahoe atmospheric deposition study (LTADS). Atmos. Environ., in press. Dubovik, O.; King, M.D. (2000). 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