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2006 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 University
EPA Project Officer: Hunt, Sherri
Project Period: September 1, 2003 through August 31, 2006 (Extended to August 31, 2007)
Project Period Covered by this Report: September 1, 2005 through August 31, 2006
Project Amount: $446,061
RFA: Measurement, Modeling, and Analysis Methods for Airborne Carbonaceous Fine Particulate Matter (PM2.5) (2003)
Research Category: Air Quality and Air Toxics , Particulate Matter
Description:
Objective:The specific aims are to:
(1) Conduct controlled laboratory experiments investigating the secondary formation of organic particulate matter (PM) through cloud/fog processing (i.e., kinetics). Results will provide critical information needed to refine predictive models, to identify potential secondary organic aerosol (SOA) “source tracers” or “process indicators” for data analysis and receptor modeling, and to guide the study of regional and local contributions to organic fine particulate matter (PM2.5) concentrations.
(2) Analyze samples from the Pittsburgh Supersite for evidence of secondary formation through cloud processing.
(3) Examine the suitability of tracers/process indicators suggested above for estimation of primary vs. secondary, local vs. regional, and/or heterogeneous vs. 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. We propose to 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). Further, we will examine evidence indicating the importance of these secondary processes in the eastern United States using U.S. Environmental Protection Agency 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. Additionally, this work will improve predictive models and therefore lead to the development of more effective air pollution control strategies.
We began the project in Year 1 by developing a simple cloud chemistry model to guide the laboratory kinetics experiments. In 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 SOA through the aqueous-phase photooxidation 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 UV and hydrogen peroxide were conducted in Year 1, and results were submitted for publication in Year 2 and have now been published 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 (e.g., Sorooshian, et al., 2006) suggesting that aqueous-phase reactions could explain the atmospheric presence of oxalic acid. In fact, it appears that oxalic acid might very well be an excellent atmospheric tracer for in-cloud or aqueous phase SOA formation. 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 has recently 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). In-cloud formation could account for or contribute to 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. In addition, glyoxal photooxidation produced large multifunctional compounds and methylglyoxal photooxidation produced a “haystack” pattern of masses in the ESI mass spectra that is consistent with oligomer formation. 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 macromolecules from these aldehyde precursors required the presence of hydroxyl radical (formed from H2O2 + UV).
In Year 3, time series data from glyoxal experiments, the initial reaction mechanism, and a commercially available equation solver (FACSIMILE) were used to expand the glyoxal photooxidation model and provide rate constants for key reactions where rate constants were yet unknown. The glyoxal experiments and reaction vessel modelling results have been presented at the American Association for Aerosol Research annual conference and a publication is in preparation (Carlton, et al., in preparation). The expanded model has been used in a box model containing aqueous and aerosol phase reactions (presented at the American Geophysical Union; Ervens, et al., 2006). Under the scenarios run, SOA yields from isoprene were approximately doubled (from 2 to 4%) by the addition of aqueous chemistry. This does not yet include the contribution of oligomers formed from methylglyoxal.
Substantial improvements also were made in the methylglyoxal mechanism in Year 3. However, the current model is not yet able to predict the concentrations observed in the reaction vessel. This might, in part, be due to the need to better incorporate oligomer formation into the model. Further progress probably requires that additional experiments be conducted, starting with compounds further down the reaction chain. This work is beyond the scope of the current project.
Our initially unexpected findings of oligomer formation have led us to conduct additional, unplanned research to better understand the composition and formation of these macromolecules. We analyzed a small number of samples from pyruvic acid and methylglyoxal reaction experiments by ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Analysis of these data is providing substantial new insights. We expect that this will solidify into a publication shortly.
We also have now conducted experiments with glyoxal + H2O2 + UV, with and without sulfuric acid (and controls). We will repeat these experiments with methylglyoxal. Data analysis is underway.
Additionally, we analyzed the dynamics of pollutant concentrations, including organic PM, measured hourly over 15 months at the Pittsburgh Supersite. This work was published in Aerosol Science and Technology (Polidori, et al., 2006). Several episodes were identified that are consistent with regional formation of SOA aloft (Polidori, et al., 2006). The presence of SOA aloft is consistent with formation through an in-cloud reaction mechanism.
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.
Sorooshian A, Varutbangkul V, Brechtel FJ, Ervens B, Feingold G, Bahreini R, Murphy SM, Holloway JS, Atlas EL, Buzorius G, Jonsson H, Flagan RC, Seinfeld JH. Oxalic acid in clear and cloudy atmospheres: analysis of data from ICARTT 2004. Journal of Geophysical Research-Atmospheres 2006;111:D23S45.
Future Activities:We will soon be submitting a paper with an expanded aqueous-phase glyoxal photooxidation mechanism for incorporation into models. We currently are analyzing ESI-MS and FT-ICR-MS data to develop insights into the composition and formation of oligomers formed from aqueous-phase photooxidation of methylglyoxal and results from glyoxal experiments in the presence/absence of sulfuric acid. These experiments will be repeated with methylglyoxal. As these results become available, they are being incorporated into our aqueous-phase chemical model. In the future, we wish to use this model to simulate the cloud processing of organics with multi-day 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.”
Journal Articles on this Report: 4 Displayed | Download in RIS Format
| Other project views: | All 28 publications | 5 publications in selected types | All 5 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 (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(L06822), doi:10.1029/2005GL025374. |
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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SOA, secondary organic aerosol, PM2.5, cloud processing, isoprene,
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Ecosystem Protection/Environmental Exposure & Risk, Air, Scientific Discipline, RFA, Engineering, Chemistry, & Physics, Air Quality, Analytical Chemistry, Air Pollution Effects, air toxics, Atmospheric Sciences, Environmental Engineering, particulate matter, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, organic pollutants, particle size measurement, aerosol analyzers, chemical characteristics, health effects, carbon aerosols, carbon particles, particulate organic carbon, ultrafine particulate matter, particulate matter mass, chemical speciation sampling, measurement methods, aerosol particles, air sampling, atmospheric dispersion models, emissions, particle dispersion, air quality modeling, air quality models, PM 2.5, atmospheric particles, atmospheric chemistry, modeling studies, air modeling, atmospheric particulate matter, airborne particulate matter, particle size, transport modeling
Progress and Final Reports:
2004 Progress Report
2005 Progress Report
Original Abstract
Final Report