Grantee Research Project Results
2005 Progress Report: Secondary and Regional Contributions to Organic PM: A Mechanistic Investigation of Organic PM in the Eastern and Southern United States
EPA Grant Number: R831073Title: Secondary and Regional Contributions to Organic PM: A Mechanistic Investigation of Organic PM in the Eastern and Southern United States
Investigators: Turpin, Barbara , Lim, Ho-Jin , Seitzinger, Sybil
Institution: Rutgers
EPA Project Officer: Chung, Serena
Project Period: September 1, 2003 through August 31, 2006 (Extended to August 31, 2007)
Project Period Covered by this Report: September 1, 2004 through August 31, 2005
Project Amount: $446,061
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003) RFA Text | Recipients Lists
Research Category: Air , Air Quality and Air Toxics , Particulate Matter
Objective:
The specific objectives of this research project are to:
- Conduct controlled laboratory experiments investigating the secondary formation of organic particulate matter (PM) through cloud/fog processing (i.e., kinetics). The results will provide critical information needed to refine predictive models, identify potential secondary organic aerosol “source tracers” or “process indicators” for data analysis and receptor modeling, and guide the study of regional and local contributions to organic fine particulate matter (PM2.5) concentrations.
- Analyze samples from the Pittsburgh Supersite for products identified in Objective 1 and examine Eastern Supersite data for evidence of heterogeneous formation to assess the relative importance of this formation process and identify conditions conducive to secondary formation through cloud processing.
- Examine the suitability of tracers/process indicators suggested above for estimation of primary versus secondary, local versus regional, and/or heterogeneous versus homogeneous contributions to ambient organic PM.
Progress Summary:
Atmospheric (secondary) formation and regional transport are responsible for a large portion of PM2.5 mass in the Eastern United States, even in urban areas. In addition, there is growing evidence suggesting that, as for sulfate, organic PM can be formed not only by homogeneous gas phase reactions but also by heterogeneous (including aqueous phase) reactions. We hypothesize that atmospheric chemistry and transport models underestimate secondary organic carbon (OC) and the regional contribution to OC in the Eastern and Southern United States because substantial organic PM is formed through heterogeneous processes (i.e., cloud processing) during regional transport. This project will provide a better understanding of fundamental atmospheric (i.e., aqueous/ heterogeneous) processes needed to predict organic PM concentration, organic species composition, and effects from emissions of particles and precursor species (i.e., improve predictive models). The research is examining evidence indicating the importance of these secondary processes in the Eastern United States using the U.S. Environmental Protection Agency (EPA) Supersite data and samples. We expect that this initial work will lead to the identification of secondary “source tracers” or “process indicators” that can be used in data analysis efforts and receptor modeling to identify the importance of primary versus secondary, local versus transport, and/or homogeneous versus heterogeneous processes. Additionally, this work will improve predictive models and therefore lead to the development of more effective air pollution control strategies.
In Year 1 of the project, we developed a simple cloud chemistry model to guide the laboratory kinetics experiments. During Year 2, the modeling results were published in Environmental Science & Technology (Lim, et al., 2005). Ervens, et al. (2004) also published model results predicting that water-soluble products of alkenes and aromatics yield secondary organic aerosol (SOA) through the aqueous-phase photooxiation of carboxylic acids and subsequent cloud droplet evaporation. The major difference between the Ervens model and ours was the fate of pyruvic acid, a product of the aqueous-phase oxidation of methylglyoxal. In the Ervens model, pyruvic acid is converted to acetaldehyde and therefore the methylglyoxal-pyruvic acid pathway does not yield SOA. In our model, based on kinetic experiments from the wastewater treatment field, pyruvic acid oxidation yields glyoxylic and oxalic acids, and therefore the methylglyoxal pathway produces SOA. The importance of the methylglyoxal-pyruvic acid pathway is illustrated by the observation that the gas-phase oxidation of isoprene yields 4.5 times more methylglyoxal than glyoxal. As a result, the fate of aqueous-phase pyruvic acid determines whether or not isoprene is an important precursor of SOA formed through cloud processing. Resolving the fate of aqueous-phase pyruvic acid is quite important to determining the yields of organic acids and SOA from cloud processing of compounds like toluene and isoprene. For this reason, we revised our planned laboratory experiments and began with an investigation of aqueous-phase pyruvic acid oxidation.
Aqueous photochemical batch reactions of pyruvic acid with and without ultraviolet (UV) and hydrogen peroxide were conducted in Year 1 and results were submitted for publication in Year 2 in Geophysical Research Letters (Carlton, et al., 2006)and Environmental Science & Technology (Altieri, et al., 2006). This work verified that glyoxylic and oxalic acid form from aqueous-phase hydroxyl radical oxidation of pyruvic acid. In addition to the expected products, oligomer formation was observed in experiments but not in controls or in standards containing mixtures of expected precursors and products (electrospray ionization-mass spectrometry [ESI-MS]; Altieri, et al., 2006). Given this, isoprene is expected to be an important precursor of SOA formed through cloud processing. This also adds to the growing body of information suggesting that aqueous-phase reactions could explain the atmospheric presence of oxalic acid. Others have reported in-cloud and below cloud measurements of oxalic acid and sulfate that support an in-cloud formation mechanism for oxalic acid (Crahan, et al., 2004). It recently has been reported that organic aerosol concentrations are elevated in the free troposphere and that these elevated concentrations cannot be explained by current models that include primary emissions and homogeneous secondary formation (Heald, et al.,2005). It is possible that in-cloud formation could account for this additional organic PM.
During Year 2, aqueous photochemical batch reactions of glyoxal and methylglyoxal with and without hydrogen peroxide and UV were performed at two levels of acidity, both in the range of those observed in fogs and clouds. Products were measured by high performance liquid chromatography with UV detection and ESI-MS. As predicted by our model, glyoxal photooxidation yielded glyoxylic, and oxalic acids; methylglyoxal photooxidation yielded pyruvic, acetic, formic, glyoxylic and oxalic acids. At higher acidity, the formation of oxalic acid was faster initially, but the oxalic acid yields at the end of the experiment were lower. Acetic acid formation was observed in controls, but oxalic acid and oligomer formation from these aldehyde precursors required the presence of hydroxyl radical (formed from H2O2 + UV). Oligomers were formed from photooxidation of both aldehydes; the mass spectra resulting from these two precursors were distinctly different.
Time series data from experiments, a reaction mechanism, and a commercially available equation solver (FACSIMILE) are now being used to provide rate constants for key reactions where rate constants are yet unknown.
Additionally, we analyzed the dynamics of pollutant concentrations, including organic PM, measured hourly for a period of 15 months at the Pittsburgh Supersite. This work was submitted to Aerosol Science and Technology in Year 2. Several episodes were identified that are consistent with regional formation of SOA aloft (Polidori, et al., 2006).
Future Activities:
We currently are analyzing data to obtain yields and reaction rate constants. We will follow this by experiments with added sulfuric acid. We will use these data to improve the chemical model we have developed. We plan to use this model to simulate the cloud processing of organics with multiday transport under conditions representative of the Eastern United States. The modeling effort will help us to understand what to look for to find “evidence of heterogeneous formation, to assess the relative importance of this formation process, and to identify conditions conducive to secondary formation through cloud processing,” as proposed in Objective 2.
References:
Crahan KK, Hegg D, Covert DS, Jonsson H. An exploration of aqueous oxalic acid production in the coastal marine atmosphere. Atmospheric Environment 2004;23:3757-3764.
Ervens B, Feingold G, Frost GJ, Kreidenweis SM. A modeling study of aqueous production of dicarboxylic acids: 1. Chemical pathways and speciated organic mass production. Journal of Geophysical Research 2004;109, doi: 10.1029/2003JD004387.
Heald CL, Jacob DJ, Park RJ, Russell LM, Heubert BJ, Seinfeld JH, Liao H, Webber RJ. A large organic aerosol source in the free troposphere missing from current models. Geophysical Research Letters 2005, 32, doi: 10.1029/2005GL023831.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 32 publications | 9 publications in selected types | All 9 journal articles |
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Altieri KE, Carlton AG, Lim H-J, Turpin BJ, Seitzinger SP. Evidence for oligomer formation in clouds: reactions of isoprene oxidation products. Environmental Science & Technology 2006;40(16):4956-4960. |
R831073 (2005) R831073 (2006) R831073 (Final) |
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Carlton AG, Turpin BJ, Lim H-J, Altieri KE, Seitzinger S. Link between isoprene and secondary organic aerosol (SOA):pyruvic acid oxidation yields low volatility organic acids in clouds. Geophysical Research Letters 2006;33(6):L06822 (4 pp.). |
R831073 (2005) R831073 (2006) R831073 (Final) |
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Lim H-J, Carlton AG, Turpin BJ. Isoprene forms secondary organic aerosol through cloud processing: model simulations. Environmental Science & Technology 2005;39(12):4441-4446. |
R831073 (2004) R831073 (2005) R831073 (2006) R831073 (Final) |
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Polidori A, Turpin BJ, Lim H-J, Cabada JC, Subramanian R, Pandis SN, Robinson AL. Local and regional secondary organic aerosol: insights from a year of semi-continuous carbon measurements at Pittsburgh. Aerosol Science and Technology 2006;40(10):861-872. |
R831073 (2005) R831073 (2006) R831073 (Final) |
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Supplemental Keywords:
SOA, secondary organic aerosol, PM2.5, cloud processing, isoprene, ecosystem protection, environmental exposure, air pollution effects, atmospheric chemistry, particulate organic carbon,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Air Quality, particulate matter, air toxics, Environmental Chemistry, Air Pollution Effects, Monitoring/Modeling, Analytical Chemistry, Environmental Monitoring, Engineering, Chemistry, & Physics, Environmental Engineering, organic pollutants, carbon aerosols, air quality modeling, particle size, atmospheric particulate matter, health effects, particulate organic carbon, atmospheric dispersion models, aerosol particles, atmospheric particles, chemical characteristics, PM 2.5, air modeling, air quality models, airborne particulate matter, air sampling, carbon particles, air quality model, emissions, particulate matter mass, ultrafine particulate matter, transport modeling, modeling studies, particle dispersion, aerosol analyzers, measurement methods, chemical speciation sampling, particle size measurementProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.