Final Report: Source-Apportionment of Primary Organic Carbon in the Eastern United States Combining Receptor-Models, Chemical Transport Models, and Laboratory Oxidation Experiments

EPA Grant Number: R832162
Title: Source-Apportionment of Primary Organic Carbon in the Eastern United States Combining Receptor-Models, Chemical Transport Models, and Laboratory Oxidation Experiments
Investigators: Robinson, Allen , Adams, Peter , Donahue, Neil
Institution: Carnegie Mellon University
EPA Project Officer: Chung, Serena
Project Period: November 1, 2004 through October 31, 2007
Project Amount: $450,000
RFA: Source Apportionment of Particulate Matter (2004) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

Organic material is a major contributor to PM2.5 mass across all regions of the United States. Given its contribution and the expected effects of past and pending reductions in SO2 and NOx emissions, an optimal strategy for attainment of the PM2.5 NAAQS may require controls on sources of organic carbon. Many PM2.5 non-attainment areas are in the Eastern United States, but significant gaps exist in our understanding of sources of organic aerosol in this region.

This research used both receptor- and emission-based modeling tools to investigate the contribution of different source classes to primary organic carbon (OC) in the Eastern United States. A major focus was on the use of organic molecular markers. The chemical stability of these markers is a critical issue in the Eastern United States, where regional transport allows for significant time for photochemical processing. Specific project objectives included:

1. To measure oxidation kinetics of organic molecular markers in actual emissions (diesel engine, wood smoke, meat cooking) exposed to O3 and OH across a wide range of atmospheric conditions in a smog chamber.

2. To apply receptor models (CMB, PMF) to molecular marker data collected by the Supersites to apportion ambient organic carbon in the Eastern United States to sources of primary organic aerosol.

3. To evaluate existing emission inventories for primary organic carbon by comparing predictions of photochemical transport models to receptor modeling results.

4. To combine receptor and chemical transport to quantify the contribution of different source classes and geographic sub-regions to primary organic carbon in the Eastern United Sates.

5. To assess the importance of photochemical aging on primary organic aerosol composition in the Eastern United States and its effects on source apportionment estimates.

Summary/Accomplishments (Outputs/Outcomes):

Objective 1: Laboratory measurements of oxidation kinetics of organic molecular markers

Laboratory experiments were conducted using the Carnegie Mellon University smog chamber to measure the oxidation rates of organic aerosols exposed to both O3 and OH. The results from this aspect of the project are described in five peer reviewed publications (1, 10, 11, 18, 19).

As part of this work we have developed a relative kinetics framework for interpretation of data on the heterogeneous oxidation of multi-component organic aerosols (Publication 1). Common accommodation, diffusion, and deposition terms cancel in this formulation, and rate constants may be determined for many compounds simultaneously within an aerosol with a realistic composition. Finally, cross-phase relative rate constants with a gas-phase reference compound and a condensed-phase target compound provide effective rate constants for use in atmospheric models.

A key component of our experimental approach was to conduct the aging experiments in a smog chamber with realistic aerosol mixtures. The smog chamber enables experiments that expose the aerosol to atmospherically relevant oxidant concentrations for time periods of hours. This avoids the potentially artificial mass transfer limitations of short duration and high oxidant concentration conditions typically used in aerosol flow tubes. Performing experiments on realistic aerosols is essential because of the significant composition dependence of heterogeneous oxidation rates. For example, Huff Hartz et al. (Publication 10) found that changing composition of simple mixtures can cause cholesterol decay rates to vary by an order of magnitude. A major conclusion from that work is that mixture effects are complicated, making it difficult to extrapolate from simple laboratory systems to atmospherically relevant conditions.

Since many molecular markers are saturated (no double bonds), the hydroxyl radical (OH) may be a more important oxidant than O3. We have developed a new laboratory source for OH radicals because of shortcomings of existing techniques in the context of heterogeneous oxidation (Publication 11). Existing methods typically require some combination of hard UV, high NOx, or extensive radical cycling. The new OH source is based on alkene ozonolysis. This OH source can consistently produce radicals in the range of (4−8) × 106 molec cm−3; these levelscan also be easily sustained over experimental time scales of many hours.

After completing this preliminary research, a series of experiments were performed to measure the oxidation kinetics molecular markers for meat cooking and motor vehicle emissions (Publications 18 and 19). Both of these experiments feature realistic aerosols exposed to atmospherically relevant oxidant concentrations for a period of 4 to 8 hours. The meat cooking experiments featured aerosols formed by flash vaporizing residual grease from cooking hamburgers. This approach mimics the processes such as splattering of grease thought to lead to emissions during cooking and produced aerosols with a composition that was indistinguishable from published meat cooking source profiles. The motor vehicle experiments featured aerosols formed by flash vaporizing new and used motor oil. Lubricating oil is thought to be the dominant component of organic aerosols in motor vehicle exhaust. The experiments also investigated the effects of varying relative humidity and secondary organic aerosol coatings on heterogeneous oxidation in order to span a wide range of atmospheric conditions. Although particle composition, relative humidity and coating all appear to influence the reaction rates, unsaturated compounds used as markers for meat cooking emissions were rapidly oxidized in every experiment. At typical summertime conditions, palmitoleic acid, oleic acid and cholesterol are estimated to have a chemical lifetime of order of one day. Hopanes and steranes (important molecular markers for motor vehicle exhaust) were found to oxidize at atmospherically significant rates across the entire range of experimental conditions. These compounds are estimated to have lifetimes on the order of several days at average summertime OH levels. The one experimental parameter that strongly influenced the effective rate constants was RH; oxidization of hopanes and steranes was about a factor of 4 slower at 75% RH than at 10% RH.

Objective 2: Application of receptor models to apportion ambient organic aerosol to primary sources in the Eastern United States

A major focus of the project has been using ambient concentrations of molecular markers to estimate sources of organic aerosol. We have written a series of papers that utilized a large dataset of ambient molecular marker concentrations developed as part of the Pittsburgh Air Quality Study (Publications 4-7, 14, 16). The unprecedented size of the dataset provided a unique opportunity to critically evaluate the use of molecular markers for source apportionment. Pittsburgh is also an interesting location because it is strongly influenced by regional transport and has large seasonal changes in weather. Finally, Pittsburgh is in the Northeast/Midatlantic region, an area of the US for which these techniques have not been previously applied. The first paper in this series (Publication 4) also describes a methodology to visualize the organization of ambient molecular marker data, to compare the data to source profiles, and to better understand receptor model solutions. The methodology can also be used to assess chemical stability and aging. The core of the technique involves construction of plots of ratios of species concentrations (ratio-ratio plots) in which source profiles appear as points connected by linear mixing lines.

Four of the papers used the visualization technique in conjunction with chemical mass balance (CMB) modeling to evaluate critical questions for small groups of compounds associated with specific source classes (e.g., levoglucosan, resin acids, and syringols as markers for biomass combustion). Are the ambient molecular marker data organized in a fashion that implies the existence of a well-defined source profile or set of profiles? Which published profiles or combinations of published profiles can explain the ambient data? How well is the amount of ambient OC apportioned to a source class constrained by CMB analysis given the set of viable profile combinations? Is there evidence of photochemical oxidation of molecular markers? These questions were examined for polycyclic aromatic hydrocarbons (Publication 4), wood smoke markers (Publication 5), meat cooking emission markers (Publication 6), and motor vehicle markers (Publication 7).

Each of these papers illustrates different strengths and challenges of using molecular markers for source apportionment. In the polycyclic aromatic hydrocarbons (PAH) example (Publication 4), an unexpected source, metallurgical coke production emissions, exerts a significant influence on the ambient PAH concentrations, greatly diminishing the feasibility of using the PAH to help specify the gasoline-diesel split. The organization of the ambient PAH data also points to significant photochemical decay of the PAHs in the regional air mass, biasing the gasoline-diesel split towards diesel emissions. Ambient data of the cooking markers (cholesterol, palmitoleic acid, oleic acid, palmitc acid, and stearic acid) form reasonably well-organized ratio-ratio plots, implying the existence of a well-defined source profile (Publication 5). However, the data do not agree with any known profiles creating challenges for CMB analysis. Motor vehicle markers (hopanes and EC) also form well-organized ratio-ratio plots, but the data exhibit a distinct seasonal pattern (Publication 7). This seasonality causes unexpected shifts in the gasoline-diesel split and therefore points to photochemical aging. The CMB estimates for gasoline vehicle emissions vary by about a factor of 10 because of significant profile-to-profile variability in emissions. Therefore, the results from CMB analysis can be very sensitive to source profile selection. Unlike molecular markers for other primary sources, the biomass burning markers (levoglucosan, syringols, and resin acids) are not well organized in the ratio-ratio plots (Publication 6). Therefore, biomass burning is an example of a source class without a distinct source profile. A consistent theme throughout the other papers is how source profile variability can be a major source of uncertainty in CMB analyses. A summary of many of the important findings from this work on using CMB to analyze molecular marker data is contained in the discussion section of Publication 6.

We also used positive matrix factorization (PMF) to analyze the Pittsburgh Air Quality Study molecular marker dataset (Publication 16). This was one of the first applications of PMF to molecular marker data. The PMF results highlight the source specific nature of molecular markers. We assessed many different PMF models using different combinations of input species and found that all of the PMF solutions found essentially the same set of factors. Six of these factors appear related to primary emissions and one to secondary organic aerosol. The amount of OC associated with these 7 core factors was, for the most part, well constrained across 21 different PMF solutions.

Two of the papers synthesize receptor modeling results across multiple studies. The first compiles the results from all of the CMB analyses (Publication 14) and the second compares results from different source apportionment models (Publication 15). In our synthesis of the CMB results we have considered uncertainty associated with selection of source profiles, selection of fitting species, sampling artifacts, photochemical aging, and unknown sources. In the context of the overall organic carbon (OC) mass balance, the contributions of diesel, woodsmoke, debris (vegetative detritus and road-dust), and coke-oven emissions are all small and well-constrained; however, estimates for the contributions of gasoline-vehicle and cooking emissions can vary by an order of magnitude depending on which species and/or profiles are included in the CMB model. A best-estimate solution is presented that represents the vast majority of the CMB results; it indicates that primary OC only contributes 27±8% and 50±14% (average ± standard deviation of daily estimates) of the ambient OC in the summer and winter in Pittsburgh, respectively. Approximately two-thirds of the primary OC is transported into Pittsburgh as part of the regional air mass. The ambient OC that is not apportioned by the CMB model is well correlated with secondary organic aerosol (SOA) estimates based on the EC-tracer method and ambient concentrations of organic species associated with SOA. Therefore, SOA appears to be the major component of OC, not only in the summer, but potentially in all seasons. Primary OC dominates the OC mass balance on a small number of non-summer days with high OC concentrations; these events are associated with specific meteorological conditions such as local inversions. Primary particulate emissions only contribute a small fraction of the ambient fine-particle mass, especially in the summer.

The source apportionment results of ambient organic aerosols based on several different techniques were synthesized in Publication 16. This paper compares PMF analysis of molecular markers, CMB analysis of molecular markers, PMF analyses of traditional speciation data, SOA estimates based on the EC-tracer method, and SOA estimates and factor analysis of Aerosol Mass Spectrometer (AMS) data. CMB and PMF analysis of molecular data and factor analysis of AMS data indicate that secondary organic aerosol is dominant in the summer, contributing between 60% and 75% of the OC. Both PMF and CMB analysis of molecular markers data indicate that primary organic aerosol emissions from motor vehicles are a relatively minor source, contributing only 10% of the annual-average OC. There was poor agreement between PMF analysis of traditional speciation and results of PMF analysis of molecular data.

Objective 3: Evaluation of emission inventories used by chemical transport models

To evaluate emission inventories used by chemical transport models, a source-resolved model was been developed to predict the contribution of eight different sources to primary organic aerosol concentrations (Publication 12). The model was applied to the Eastern United States during a seventeen day pollution episode beginning on July 12, 2001. Primary organic matter (OM) and elemental carbon (EC) concentrations are tracked for eight different sources: gasoline vehicles, non-road diesel vehicles, on-road diesel vehicles, biomass burning, wood burning, natural gas combustion, road dust, and all other sources. Individual emission inventories are developed from a modified version of the NEI 1999 for each source and a three-dimensional chemical transport model (PMCAMx+) is used to predict the primary OM and EC concentrations from each source. The source-resolved model is simple to implement and is faster than the existing source-oriented models.

The predictions of the source-resolved model were compared to measurements from the STN and IMPROVE networks. Reasonable agreement is observed in the predicted total OM and the ambient data, but the model predicts EC concentrations three times higher than measurements from STN. Significant discrepancies exist if one compares the source-resolved predictions to the results of chemical mass balance models (CMB) for Pittsburgh and Atlanta. Significant discrepancies exist between the source-resolved model predictions and the CMB model predictions for some of the sources. For EC, non-road diesel, according to the emission inventory, is predicted to contribute more to EC in urban areas than on-road diesel. This overprediction suggests that the non-road diesel emission inventory is currently too high. While the non-road diesel inventory should be reduced, the on-road diesel emission inventory may also need to be reduced.

Natural gas, wood burning and biomass burning are other sources that have emission inventory problems. The most striking problems are observed for natural gas; the primary OM emission inventory for natural gas should be reduced by at least 50 times the current value.

Objective 5: To assess the importance of photochemical aging on primary organic aerosol composition

We employed two approaches to assess the importance of photochemical aging on primary organic aerosol composition. The first was based on analysis of ambient molecular marker data collected as part of the Pittsburgh Air Quality Study (Publications 2, 4, 7). We found evidence that condensed-phase organic compounds are significantly oxidized in regional air masses and in locations affected by regional transport, especially during the summer. For example, there is a strong seasonal pattern in the ratio of different hopanes to elemental carbon consistent with oxidation. In addition, measurements at rural sites indicate that hopanes are severely depleted in the regional air mass during the summer. The ambient data also indicates that alkenoic acids are being photochemically oxidized during the summertime; however, the oxidation rate appears to be much slower than that inferred from laboratory experiments on simple systems.

The strong seasonal pattern in the hopanes-to-EC ratios causes a CMB to predict a seasonal shift in the relative importance of primary emissions from gasoline vehicles to ambient OC (Publications 2 and 7). In the summer when hopanes-to-EC ratios are small and most CMB solutions indicate negligible amounts of primary OC from gasoline vehicles. In contrast, CMB predicts substantial amounts of gasoline vehicle OC predicted by CMB in the winter. Therefore, photo-oxidation of molecular marker appears to be significantly influencing critical first order source apportionment questions such as the net contribution of motor vehicle emissions and the gasoline-diesel split.

The conclusions drawn from the analysis of the Pittsburgh Air Quality Study molecular marker data are supported by our laboratory results (Publications 18 and 19). For example, at low RH conditions, the laboratory data indicate that more than half of the hopanes are oxidized within two days of emission. At high RH conditions between 25 to 75% of hopanes will be oxidized after a week. Laboratory data indicate that unsaturated compounds (cholesterol, oleic acid, palmitoleic) are oxidized even faster than the hopanes and steranes. Therefore oxidation may influence marker concentrations in local emissions.

The kinetic data measured in the laboratory as part of Objective 1 were also used in conjunction with the Chemical Mass Balance model to investigate the potential effects of oxidation on source apportionment estimates (Publications 18 and 19). For example, oxidation causes CMB to underestimate the total contribution motor vehicles. However, oxidation has different effects on the source contribution estimates of gasoline and diesel vehicles. As the extent of oxidation increases, the estimated gasoline contribution becomes more biased (low) but the diesel estimates are largely unaffected. These trends can be understood by examining how CMB fits gasoline and diesel vehicles (Publication 7).

Other work:

In addition to the pursuing the stated objectives of this project we also pursued research on gas particle portioning of primary organic aerosol emissions that emerged from our EPA supported Supersite Project. This work has the potential to transform our understanding of organic particle behavior in the atmosphere, with major findings published in Science (Publication 9). Most primary organic particulate emissions are semivolatile; they thus partially evaporate with atmospheric dilution, creating significant amounts of low-volatility gas-phase material (Publication 8). Laboratory experiments show that photo-oxidation of diesel emissions rapidly generates organic aerosol, greatly exceeding the contribution from known secondary organic aerosol precursors (Publications 9, 13, 17). We attribute this unexplained secondary organic aerosol production to oxidation of low volatility gas-phase species. Accounting for both gas-particle partitioning and photochemical processing of primary emissions creates a regional aerosol and brings model predictions into better agreement with observations (Publication 20). This finding has important implications for how we measure and simulate organic aerosol, blurring the dual notion of secondary and primary organic aerosol.

Conclusions:

There are numerous conclusions and practical implications from this work:

  • Compounds used as molecular markers rapidly oxidize in simple systems, but the oxidation rates strongly depend on mixture composition. Data in realistic systems (hamburger grease and motor oil) show significant decay of markers at atmospherically relevant oxidant concentrations.
  • Both ambient and laboratory data indicates that oxidation likely alters source apportionment estimates using molecular markers in locations with significant regional transport. In fact, even modest levels of oxidation can alter policy-relevant conclusions such as the gasoline-diesel split.
  • Even in Pittsburgh, a location strongly influenced by regional transport, molecular marker concentrations contain significant source information. Therefore, molecular markers are an essential tool for source apportionment studies. However, future studies must consider both mixing of emissions and oxidation as first-order processes.
  • Source profile variability creates substantial uncertainties for source apportionment analyses. These uncertainties need to be explicitly accounted for in future source apportionment studies that utilize molecular marker data.
    • There are clear problems with the existing emission inventories for chemical transport models used for SIP development. The most striking problems are observed for natural gas; the primary organic aerosol emission inventory for natural gas should be reduced by at least 50 times the current value. Problems were also observed for biomass burning and non-road diesel.
  • The semivolatile character of primary emissions means that instead of measuring fixed primary organic aerosol emissions factors, we must measure the volatility distribution of the emissions.
  • Models and inventories must account for these distributions and their evolution with photochemical age.
    • Low volatility organics are an important source of secondary organic aerosol that are poorly accounted for in current models and inventories.
  • Both PMF and CMB analysis of molecular marker data indicate that secondary organic aerosol contributes around two-thirds of the ambient organic aerosol in the summer in the Eastern United States. Except for people living close to sources, the majority of the population, even in urban areas, is exposed mostly to SOA.


Journal Articles on this Report : 26 Displayed | Download in RIS Format

Other project views: All 75 publications 26 publications in selected types All 26 journal articles
Type Citation Project Document Sources
Journal Article Donahue NM, Robinson AL, Huff Hartz KE, Sage AM, Weitkamp EA. Competitive oxidation in atmospheric aerosols: the case for relative kinetics. Geophysical Research Letters 2005;32:L16805. R832162 (2005)
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  • Journal Article Donahue NM, Robinson AL, Stanier CO, Pandis SN. Coupled partitioning, dilution, and chemical aging of semivolatile organics. Environmental Science & Technology 2006;40(8):2635-2643. R832162 (2005)
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  • Journal Article Grieshop AP, Donahue NM, Robinson AL. Is the gas-particle partitioning in alpha-pinene secondary organic aerosol reversible? Geophysical Research Letters 2007;34:L14810. R832162 (Final)
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  • Journal Article Huff Hartz KE, Weitkamp EA, Sage AM, Donahue NM, Robinson AL. Laboratory measurements of the oxidation kinetics of organic aerosol mixtures using a relative rate constants approach. Journal of Geophysical Research-Atmospheres 2007;112(D4):D04204 (13 pp.). R832162 (2005)
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  • Journal Article Lambe AT, Zhang J, Sage AM, Donahue NM. Controlled OH radical production via ozone-alkene reactions for use in aerosol aging studies. Environmental Science & Technology 2007;41(7):2357-2363. R832162 (2005)
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  • Journal Article Lane TE, Pandis SN. Predicted secondary organic aerosol concentrations from the oxidation of isoprene in the eastern United States. Environmental Science & Technology 2007;41(11):3984-3990. R832162 (Final)
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  • Journal Article Lane TE, Pinder RW, Shrivastava M, Robinson AL, Pandis SN. Source contributions to primary organic aerosol:Comparison of the results of a source-resolved model and the chemical mass balance approach. Atmospheric Environment 2007;41(18):3758-3776. R832162 (2005)
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  • Journal Article Pierce JR, Engelhart GJ, Hildebrandt L, Weitkamp EA, Pathak RK, Donahue,NM, Robinson AL, Adams PJ, Pandis SN. Constraining particle evolution from wall losses, coagulation, and condensation-evaporation in smog-chamber experiments: optimal estimation based on size distribution measurements. Aerosol Science and Technology 2008;42(12):1001-1015. R832162 (Final)
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  • Journal Article Presto AA, Huff Hartz KE, Donahue NM. Secondary organic aerosol production from terpene ozonolysis. 1. Effect of UV radiation. Environmental Science & Technology 2005;39(18):7036-7045. R832162 (Final)
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  • Journal Article Presto AA, Huff Hartz KE, Donahue NM. Secondary organic aerosol production from terpene ozonolysis. 2. Effect of NOx concentration. Environmental Science & Technology 2005;39(18):7046-7054. R832162 (Final)
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  • Journal Article Robinson AL, Subramanian R, Donahue NM, Bernardo-Bricke A, Rogge WF. Source apportionment of molecular markers and organic aerosol--1. Polycyclic aromatic hydrocarbons and methodology for data visualization. Environmental Science & Technology 2006;40(24):7803-7810. R832162 (2005)
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  • Journal Article Robinson AL, Subramanian R, Donahue NM, Bernardo-Bricker A, Rogge WF. Source apportionment of molecular markers and organic aerosol. 2. Biomass smoke. Environmental Science & Technology 2006;40(24):7811-7819. R832162 (2005)
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  • Journal Article Robinson AL, Subramanian R, Donahue NM, Bernardo-Bricker A, Rogge WF. Source apportionment of molecular markers and organic aerosol. 3. Food cooking emissions. Environmental Science & Technology 2006;40(24):7820-7827. R832162 (2005)
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  • Journal Article Robinson AL, Donahue NM, Rogge WF. Photochemical oxidation and changes in molecular composition of organic aerosol in the regional context. Journal of Geophysical Research-Atmospheres 2006;111(D3):D03302 (15 pp.). R832162 (2005)
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  • Journal Article Robinson AL, Donahue NM, Shrivastava MK, Weitkamp EA, Sage AM, Grieshop AP, Lane TE, Pierce JR, Pandis SN. Rethinking organic aerosols: semivolatile emissions and photochemical aging. Science 2007;315(5816):1259-1262. R832162 (2006)
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  • Journal Article Rudich Y, Donahue NM, Mentel TF. Aging of organic aerosol: bridging the gap between laboratory and field studies. Annual Review of Physical Chemistry 2007;58:321-352. R832162 (Final)
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  • Journal Article Sage AM, Weitkamp EA, Robinson AL, Donahue NM. Evolving mass spectra of the oxidized component of organic aerosol: results from aerosol mass spectrometer analyses of aged diesel emissions. Atmospheric Chemistry and Physics 2008;8(5):1139-1152. R832162 (Final)
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  • Journal Article Sage AM, Weitkamp EA, Robinson AL, Donahue NM. Reactivity of oleic acid in organic particles: changes in oxidant uptake and reaction stoichiometry with particle oxidation. Physical Chemistry Chemical Physics 2009;11(36):7951-7962. R832162 (Final)
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  • Journal Article Shrivastava MK, Lipsky EM, Stanier CO, Robinson AL. Modeling semivolatile organic aerosol mass emissions from combustion systems. Environmental Science & Technology 2006;40(8):2671-2677. R832162 (2005)
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  • Journal Article Shrivastava MK, Subramanian R, Rogge WF, Robinson AL. Sources of organic aerosol:positive matrix factorization of molecular marker data and comparison of results from different source apportionment models. Atmospheric Environment 2007;41(40):9353-9369. R832162 (Final)
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  • Journal Article Shrivastava MK, Lane TE, Donahue NM, Pandis SN, Robinson AL. Effects of gas particle partitioning and aging of primary emissions on urban and regional organic aerosol concentrations. Journal of Geophysical Research-Atmospheres 2008;113(D18):D18301 (16 pp.). R832162 (Final)
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  • Journal Article Subramanian R, Donahue NM, Bernardo-Bricker A, Rogge WF, Robinson AL. Contribution of motor vehicle emissions to organic carbon and fine particle mass in Pittsburgh, Pennsylvania:effects of varying source profiles and seasonal trends in ambient marker concentrations. Atmospheric Environment 2006;40(40):8002-8019. R832162 (2005)
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  • Journal Article Subramanian R, Donahue NM, Bernardo-Bricker A, Rogge WF, Robinson AL. Insights into the primary--secondary and regional--local contributions to organic aerosol and PM2.5 mass in Pittsburgh, Pennsylvania. Atmospheric Environment 2007;41(35):7414-7433. R832162 (Final)
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  • Journal Article Weitkamp EA, Sage AM, Pierce JR, Donahue NM, Robinson AL. Organic aerosol formation from photochemical oxidation of diesel exhaust in a smog chamber. Environmental Science & Technology 2007;41(20):6969-6975. R832162 (Final)
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  • Journal Article Weitkamp EA, Lambe AT, Donahue NM, Robinson AL. Laboratory measurements of the heterogeneous oxidation of condensed-phase organic molecular makers for motor vehicle exhaust. Environmental Science & Technology 2008;42(21):7950-7956. R832162 (Final)
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  • Journal Article Weitkamp EA, Huff Hartz KE, Sage AM, Donahue NM, Robinson AL. Laboratory measurements of the heterogeneous oxidation of condensed-phase organic molecular makers for meat cooking emissions. Environmental Science & Technology 2008;42(14):5177-5182. R832162 (Final)
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  • Supplemental Keywords:

    RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Air Quality, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, particulate organic carbon, atmospheric dispersion models, atmospheric measurements, model-based analysis, source apportionment, chemical characteristics, emissions monitoring, environmental measurement, airborne particulate matter, air quality models, air quality model, air sampling, speciation, particulate matter mass, analytical chemistry, modeling studies, chemical transport models, real-time monitoring, aerosol analyzers, chemical speciation sampling, particle size measurement, atmospheric chemistry

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    Progress and Final Reports:

    Original Abstract
  • 2005 Progress Report
  • 2006 Progress Report