Final Report: Sources of Organic Aerosol: Semivolatile Emissions and Photochemical Aging

EPA Grant Number: R833748
Title: Sources of Organic Aerosol: Semivolatile Emissions and Photochemical Aging
Investigators: Robinson, Allen , Adams, Peter
Institution: Carnegie Mellon University
EPA Project Officer: Chung, Serena
Project Period: September 1, 2007 through August 31, 2010 (Extended to October 31, 2011)
Project Amount: $600,000
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air

Objective:

Organic aerosol is a major component of fine particulate matter in essentially all regions of the atmosphere. However, chemical transport models generally underpredict measured organic aerosol concentrations, complicating the development of effective policy actions to improve air quality. This project performed laboratory experiments to investigate the effects of gas-particle partitioning and photochemical aging on organic aerosol emissions from important combustion systems. Parameterizations of these findings were implemented in air-quality models, which were used to quantify the effects of partitioning and aging on ambient organic aerosol levels. The ultimate objective of the research is to better understand the contribution of human activity to organic aerosol levels to enable and inform policy actions aimed at improving air quality.

Summary/Accomplishments (Outputs/Outcomes):

Predicting primary and secondary organic aerosol (SOA) concentrations requires understanding the sources and phase partitioning of very complex mixtures of organic species. Combustion is a major source of air pollutants. At the source, combustion emissions are concentrated and hot. Upon entering the atmosphere, the emissions mix with background air, cooling and diluting the exhaust, which alters the gas-particle partitioning of condensable vapors. Once in the atmosphere, the emissions are exposed to sunlight, other pollutants, and oxidants, which causes them to evolve chemically and physically. Secondary organic aerosol is formed in the atmosphere from chemical reactions of organic gases and vapors that create low-volatility products that partition into the particle phase. Both the primary and secondary organic aerosol must be defined to quantify the overall contribution of a combustion system to ambient fine particulate matter mass.

In this project a series of laboratory experiments were performed to investigate the effects of gasparticle partitioning and photochemical aging on organic aerosol emissions from combustion systems. The experiments were conducted with mixtures of different complexity, ranging from dilute emissions from real sources (e.g., wood stove) to emissions surrogates (e.g., evaporate fuel) to individual chemical species. By systematically studying systems of varying complexity, we gained significant new understanding on the atmospheric evolution of emissions from combustion systems.

We systematically investigated the gas-particle partitioning of primary organic aerosol emissions from a diesel engine and a wood stove. We also investigated the gas-particle partitioning of two flash vaporized lubricating oil, which is thought to be an important component of primary organic aerosol emissions from motor vehicles. The partitioning experiments were performed using multiple techniques, including isothermal dilution using both dilution sampler and a smog chamber, and heating using a thermodenuder. Smog chambers had not been previously used to characterize gas-particle partitioning behavior of primary organic aerosol emissions from combustion sources. The technique involves slowly filling a Teflon chamber with a constant emission source. As aerosol concentrations increase inside the chamber, the gas-particle partitioning of semivolatile organics shifts to the particle phase, increasing the fuel-based primary organic aerosol emission factor. The technique allows characterization of partitioning under isothermal conditions and typical atmospheric concentrations.

The partitioning experiments investigated a wide range of atmospheric conditions, including low concentrations and small temperature perturbations. The partitioning of the primary organic aerosol emissions from both the diesel engine and wood stove varied continuously with changing concentrations and temperature. In fact, the data indicate that wood smoke and diesel primary organic aerosol are quite “volatile”; for example, almost all of the primary organic aerosol emitted by both sources evaporated at temperatures less than 100°C. The overall partitioning characteristics of diesel and wood smoke primary organic aerosol are similar, with wood smoke being somewhat less volatile than the diesel exhaust. The data from the different techniques were fit to absorptive partition theory using the volatility-basis-set framework. These fields yield volatility distributions that quantitatively reproduced the gas-particle partitioning of bulk primary organic aerosol and are designed for use in chemical transport models. The results illustrate how these complimentary techniques can be used to constrain the gas-particle partitioning over a wide range of atmospheric conditions. The practical implication of the gas-particle partitioning measurements is that both primary organic aerosol in diesel exhaust and wood smoke is semivolatile not non-volatile as currently assumed by chemical transport models for state implementation plan (SIP) development.

Another major objective of the experimental research was to investigate the secondary organic aerosol formation from photo-oxidation of emissions to better understand the persistent discrepancies between ambient observations and chemical-transport-model predictions. We conducted smog chamber experiments to photo-oxidize dilute emissions from a wood stove and small diesel engine. We also conducted experiments with individual compounds to systematically investigate the effects of molecular structure on secondary organic aerosol formation.

The experiments with dilute emissions underscore how atmospheric processing can lead to considerable evolution of the mass and volatility of emissions from a combustion system. It also substantially enhanced the organic aerosol. Less than 20% of this new organic aerosol could be explained using a state-of-the-art SOA model and the measured decay of traditional SOA precursors. The predictions of a volatility-basis-set model that explicitly tracks the partitioning and aging of low-volatile organics were compared to the chamber data. The organic aerosol production can be explained by the oxidation of low-volatility organic vapors; the model also can reproduce observed changes in organic aerosol volatility and composition. The model was used to investigate the competition between photochemical processing and dilution on organic aerosol concentrations in plumes.

In addition to the experiments with dilute exhaust, mixtures of low-volatility organics were photo-oxidized in a smog chamber under low- and high-NOx conditions. Separate experiments addressed emission surrogates (diesel fuel and motor oil) and single components (n-alkanes). Both diesel fuel and motor oil are major components of exhaust from diesel engines. Diesel fuel is a complex mixture of intermediate volatility organic compounds while motor oil is a complex mixture of semivolatile organic compounds. Intermediate volatility organic compounds exist exclusively in the vapor phase, while semivolatile organic compounds exist in both the aerosol and vapor phase. Oxidation of semivolatile organics (motor oil and n-pentacosane) creates substantial SOA, but this SOA is largely offset by evaporation of primary organic aerosol. The net effect is a cycling or pumping of semivolatile organics between the gas and particle phases, which creates more oxygenated organic aerosol but little new organic aerosol mass. Because gas-phase reactions are much faster than heterogeneous ones, the processing of semivolatile organic vapors likely contributes to the production of highly oxidized organic aerosol. The interplay between gas-particle partitioning and chemistry also blurs traditional definitions of primary and secondary organic aerosol.

Photo-oxidation of diesel fuel intermediate volatility organic compounds (diesel fuel) rapidly creates substantial new organic aerosol mass, similar to our work with dilute diesel exhaust. However, aerosol mass spectrometer data indicated that the SOA formed from emission surrogates is less oxidized than either the oxygenated organic aerosol measured in the atmosphere or SOA formed from the photo-oxidation of dilute diesel exhaust. Therefore, photo-oxidation of intermediate volatility organic compounds helps explain the substantial SOA mass produced from aging diesel exhaust, but some component is missing from these emissions surrogate experiments that leads to the rapid production of highly oxygenated SOA.

We also systematically investigated SOA formation from different homologous series of intermediate and semivolatile organic compounds, focusing on n-alkanes. The experiments feature atmospheric relevant organic aerosol concentrations. Under high-NOx conditions, SOA yields increased with increasing carbon number (lower volatility) for n-decane, n-dodecane, n-pentadecane, and n-heptadecane. As with other photo-oxidation systems, aerosol yield increased with UV intensity. Due to the log-linear relationship between n-alkane carbon number and vapor pressure, as well as a relatively consistent product distribution, it was possible to develop an empirical parameterization for SOA yields for n-alkanes between C10 and C20. This parameterization was implemented using the volatility-basis-set framework and is designed for use in chemical transport models. At low organic aerosol concentrations, the SOA mass spectrum, as measured with an aerosol mass spectrometer, had a large contribution from m/z 44, indicative of highly oxygenated products. At higher organic aerosol concentrations, the mass spectrum was dominated by m/z 30, indicative of organic nitrates.

There are two practical consequences of the photochemical aging work. First, photo-oxidation of dilute exhaust from combustion systems investigated in this project produced substantial amounts of secondary organic aerosol that cannot be explained using current atmospheric chemistry models, highlighting the problems with these models. Second, photo-oxidation of four low volatility organic vapors can produce SOA with a mass spectrum that is similar to ambient data. Therefore, low-volatility organic vapors appear to be an important class of precursors that is largely unaccounted for in current chemical transport models used for SIP development.

The new laboratory data (emissions and SOA formation) were parameterized using the volatility-basis-set framework for use in chemical transport model. These parameterizations were published to facilitate use by other researchers.

Chemical transport modeling was performed on both the regional and global scale to investigate the effects of gas-particle partitioning and photochemical aging on primary emissions. The regional simulations were performed using PMCAMx and the global simulations were performed using the GISS GCM II’ “unified” climate model. Both models were modified to simulate semivolatile and reactive primary organic aerosols using the volatility-basis-set framework. The models were evaluated by comparing predictions to a broad set of observational constraints including organic aerosol mass concentrations, degree of oxygenation, volatility and isotopic composition. A traditional model that treats primary organic aerosol as non-volatile and non-reactive also is compared to the same set of observations to highlight changes due to the revised treatment.

The revised models that explicitly account for partitioning and aging of primary emissions predict that SOA is the dominant component of organic aerosol levels. This change brings the primary-secondary organic split into much better agreement with ambient measurements. This change is due to traditionally defined primary organic aerosol evaporating and the evaporated vapors oxidizing to form non-traditional SOAs. A second important finding of the modeling was that intermediate volatile organic compounds (traditionally not included in chemical transport models) oxidize to form condensable products that can contribute significantly to organic aerosol levels. This suggests that models (both regional and global) may be missing an important source of organic aerosol. However, emissions of intermediate volatility organic compounds are not routinely measured during source tests and therefore are uncertain. Sensitivity analyses were performed to quantify the effects of this uncertainty on predicted organic aerosol levels. Overall, the model evaluation highlights the importance of treating primary organic aerosol as semivolatile and reactive in order to predict accurately the sources, composition and properties of ambient organic aerosol.

The practical implication of the modeling component of the research is that explicit accounting for partitioning and aging of primary emissions improves predictions of chemical transport models used for SIP development and evaluating the effects of climate change on urban and regional air quality.


Journal Articles on this Report : 21 Displayed | Download in RIS Format

Other project views: All 83 publications 21 publications in selected types All 21 journal articles
Type Citation Project Document Sources
Journal Article Ahmadov R, McKeen SA, Robinson AL, Bahreini R, Middlebrook AM, de Gouw JA, Meagher J, Hsie E-Y, Edgerton E, Shaw S, Trainer M. A volatility basis set model for summertime secondary organic aerosols over the eastern United States in 2006. Journal of Geophysical Research–Atmospheres 2012;117(D6):D06301 (19 pp.). R833748 (Final)
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  • Journal Article Asa-Awuku A, Miracolo MA, Kroll JH, Robinson AL, Donahue NM. Mixing and phase partitioning of primary and secondary organic aerosols. Geophysical Research Letters 2009;36(15):L15827 (5 pp.). R833748 (2010)
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  • Journal Article de Gouw JA, Middlebrook AM, Warneke C, Ahmadov R, Atlas EL, Bahreini R, Blake DR, Brock CA, Brioude J, Fahey DW, Fehsenfeld FC,Holloway JS, Le Henaff M, Lueb RA, McKeen SA, Meagher JF, Murphy DM, Paris C, Parrish DD, Perring AE, Pollack IB, Ravishankara AR, Robinson AL, Ryerson TB, Schwarz JP, Spackman JR, Srinivasan A, Watts LA. Organic aerosol formation downwind from the Deepwater Horizon oil spill. Science 2011;331(6022):1295-1299. R833748 (Final)
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  • Journal Article Donahue NM, Robinson AL, Pandis SN. Atmospheric organic particulate matter: from smoke to secondary organic aerosol. Atmospheric Environment 2009;43(1):94-106. R833748 (2008)
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  • Journal Article Grieshop AP, Logue JM, Donahue NM, Robinson AL. Laboratory investigation of photochemical oxidation of organic aerosol from wood fires 1: measurement and simulation of organic aerosol evolution. Atmospheric Chemistry and Physics 2009;9(4):1263-1277. R833748 (2008)
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  • Journal Article Grieshop AP, Miracolo MA, Donahue NM, Robinson AL. Constraining the volatility distribution and gas-particle partitioning of combustion aerosols using isothermal dilution and thermodenuder measurements. Environmental Science & Technology 2009;43(13):4750-4756. R833748 (2008)
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  • Journal Article Grieshop AP, Donahue NM, Robinson AL. Laboratory investigation of photochemical oxidation of organic aerosol from wood fires 2: analysis of aerosol mass spectrometer data. Atmospheric Chemistry and Physics 2009;9(6):2227-2240. R833748 (2008)
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  • Journal Article Jathar SH, Farina SC, Robinson AL, Adams PJ. The influence of semi-volatile and reactive primary emissions on the abundance and properties of global organic aerosol. Atmospheric Chemistry and Physics 2011;11(15):7727-7746. R833748 (2010)
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  • Journal Article Jathar SH, Donahue NM, Adams PJ, Robinson AL. Testing secondary organic aerosol models using smog chamber data for complex precursor mixtures: influence of precursor volatility and molecular structure. Atmospheric Chemistry and Physics 2014;14(11):5771-5780. R833748 (Final)
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  • Journal Article Jimenez JL, Canagaratna MR, Donahue NM, Prevot AS, Zhang Q, Kroll JH, DeCarlo PF, Allan JD, Coe H, Ng NL, Aiken AC, Docherty KS, Ulbrich IM, Grieshop AP, Robinson AL, Duplissy J, Smith JD, Wilson KR, Lanz VA, Hueglin C, Sun YL, Tian J, Laaksonen A, Raatikainen T, Rautiainen J, Vaattovaara P, Ehn M, Kulmala M, Tomlinson JM, Collins DR, Cubison MJ, Dunlea EJ, Huffman JA, Onasch TB, Alfarra MR, Williams PI, Bower K, Kondo Y, Schneider J, Drewnick F, Borrmann S, Weimer S, Demerjian K, Salcedo D, Cottrell L, Griffin R, Takami A, Miyoshi T, Hatakeyama S, Shimono A, Sun JY, Zhang YM, Dzepina K, Kimmel JR, Sueper D, Jayne JT, Herndon SC, Trimborn AM, Williams LR, Wood EC, Middlebrook AM, Kolb CE, Baltensperger U, Worsnop DR. Evolution of organic aerosols in the atmosphere. Science 2009;326(5959):1525-1529. R833748 (2010)
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  • Journal Article Lambe AT, Miracolo MA, Hennigan CJ, Robinson AL, Donahue NM. Effective rate constants and uptake coefficients for the reactions of organic molecular markers (n-alkanes, hopanes, and steranes) in motor oil and diesel primary organic aerosols with hydroxyl radicals. Environmental Science & Technology 2009;43(23):8794-8800. R833748 (Final)
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  • Journal Article May AA, Presto AA, Hennigan CJ, Nguyen NT, Gordon TD, Robinson AL. Gas-particle partitioning of primary organic aerosol emissions: (2) diesel vehicles. Environmental Science & Technology 2013;47(15):8288-8296. R833748 (Final)
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  • Journal Article May AA, Presto AA, Hennigan CJ, Nguyen NT, Gordon TD, Robinson AL.Gas-particle partitioning of primary organic aerosol emissions: (1) gasoline vehicle exhaust. Atmospheric Environment 2013;77:128-139. R833748 (Final)
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  • Journal Article Miracolo MA, Presto AA, Lambe AT, Hennigan CJ, Donahue NM, Kroll JH, Worsnop DR, Robinson AL. Photo-oxidation of low-volatility organics found in motor vehicle emissions: production and chemical evolution of organic aerosol mass. Environmental Science & Technology 2010;44(5):1638-1643. R833748 (2010)
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  • Journal Article Presto AA, Miracolo MA, Kroll JH, Worsnop DR, Robinson AL, Donahue NM. Intermediate-volatility organic compounds: a potential source of ambient oxidized organic aerosol. Environmental Science & Technology 2009;43(13):4744-4749. R833748 (2008)
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  • Journal Article Presto AA, Miracolo MA, Donahue NM, Robinson AL. Secondary organic aerosol formation from high-NOx photo-oxidation of low volatility precursors:n-alkanes. Environmental Science & Technology 2010;44(6):2029-2034. R833748 (2010)
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  • Journal Article Presto AA, Gordon TD, Robinson AL. Primary to secondary organic aerosol: evolution of organic emissions from mobile combustion sources. Atmospheric Chemistry and Physics 2014;14(10):5015-5036. R833748 (Final)
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  • Journal Article Ranjan M, Presto AA, Robinson AL. Temperature dependence of gas-particle partitioning of primary organic aerosol emissions from a small diesel engine. Aerosol Science and Technology 2012;46(1):13-21. R833748 (2010)
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  • Journal Article Robinson AL, Grieshop AP, Donahue NM, Hunt SW. Updating the conceptual model for fine particle mass emissions from combustion systems. Journal of the Air & Waste Management Association 2010;60(10):1204-1222. R833748 (2010)
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  • Journal Article Saleh R, Donahue NM, Robinson AL. Time scales for gas-particle partitioning equilibration of secondary organic aerosol formed from alpha-pinene ozonolysis. Environmental Science & Technology 2013;47(11):5588-5594. R833748 (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.). R833748 (2008)
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  • Supplemental Keywords:

    Airborne particulate matter, aerosol, emission characterization, atmospheric chemistry, regional modeling, source/receptor analysis, global modeling photochemistry

    Relevant Websites:

    Center for Atmospheric Particle Studies (CAPS) | Carnegie Mellon University Exit

    Progress and Final Reports:

    Original Abstract
  • 2008 Progress Report
  • 2009 Progress Report
  • 2010 Progress Report
  • 2011