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Final 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 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:
- Conduct controlled laboratory experiments investigating the secondary formation of organic particulate matter through cloud/fog processing (i.e., kinetics). Results will provide critical information needed to refine predictive models, to identify potential secondary organic aerosol “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.
- Analyze samples from the Pittsburgh Supersite for evidence of secondary formation through cloud processing.
- 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.
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, secondary organic aerosol (SOA) can be formed not only by homogeneous gas phase reactions, but also by heterogeneous (including aqueous-phase) reactions. We hypothesized that atmospheric chemical transport models underestimate SOA and the regional contribution to particulate organic carbon (OC) in the eastern and southern United States because substantial OC is formed through cloud processing during regional transport. Specifically, we hypothesized that alkenes and aromatics are oxidized in the interstitial spaces of clouds to form water-soluble species (e.g., glyoxal, methylglyoxal) that partition into cloud droplets. They oxidize further in the aqueous phase forming low volatility products (e.g., oxalic acid). Upon cloud droplet evaporation, these products contribute SOA (Blando et al., 2001).
In the current project we investigated this mechanism through laboratory experiments, field measurements, and chemical kinetic modeling. The laboratory studies provided strong evidence that oxalic acid, other organic acids, and large multifunctional compounds including oligomers form in the aqueous phase from glyoxal, methylglyoxal, and intermediates (pyruvic acid) in the presence of hydroxyl radicals under conditions found in atmospheric waters (clouds and aerosol water). This result provides strong support for the hypothesis that SOA forms through cloud processing. Measurements from an EPA Supersite experiment in Pittsburgh, PA produced evidence consistent with a source of SOA aloft, such as cloud processing (Polidori et al., 2006). Because primary emission and other identified secondary formation mechanisms are not sufficient to explain the atmospheric burden of oxalic acid, the results of the current project suggest that oxalic acid is a potentially good candidate for use as an indicator of SOA formation through aqueous chemistry (i.e., in clouds, fogs and aerosol water). Incorporation of our laboratory and field results on SOA formation through cloud processing into a chemical transport model (CMAQ; collaborative research) resulted in substantially improved agreement with aircraft measurements for August 2004 (ICARTT study). Thus, it appears that the inclusion of this SOA formation mechanism in chemical transport models will aid the development of more effective air pollution control strategies. The current research has provided a better understanding of fundamental atmospheric (i.e. aqueous phase) processes needed to predict organic particulate matter concentrations, organic species composition, and effects from emissions of particles and precursor species (i.e. improve predictive models). In the following section we provide additional details of this research.
Early in the project we built a cloud chemistry mechanism based on the available literature to guide the laboratory kinetics experiments(Lim et al., 2005). (The entire chemical mechanism is published in Supporting Information, Environ. Sci. Technol.) Ervens et al. (2004) independently published a proposed cloud chemistry mechanism within a cloud parcel model. Both mechanisms predicted 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. However, both mechanisms were largely based on laboratory experiments where products were not measured. 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.
We conducted aqueous photochemical batch reactions of pyruvic acid, glyoxal and methylglyoxal with hydroxyl radical (i.e., formed from UV plus hydrogen peroxide). In some cases these experiments verified assumptions made in the previously published modeling papers, in other cases these experiments yielded substantial new findings. Product analysis verified that oxalic acid forms from pyruvic acid (Carlton et al., 2006), glyoxal (Carlton et al., 2007a), and methylglyoxal (Altieri et al., 2007, Carlton et al., submitted) at cloud-relevant pH, as assumed by Lim et al (2005).Oxalic acid/oxalate is the most abundant particle-phase organic acid in the atmosphere. This result, together with the chemical modeling, provides strong evidence for SOA formation through cloud processing. This result clarifies the fate of pyruvic acid, and suggests that isoprene is an important precursor of SOA formed through cloud processing, as predicted by Lim et al (2005). This also adds to the growing body of information (e.g., Sorooshian et al., 2006; Chebbi and Carlier, 1996) suggesting that aqueous-phase reactions (i.e., in clouds, fogs and aerosol water) 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 (e.g., Crahan et al., 2004; Yu et al., 2005).
In addition to the expected products, large multifunctional compounds with acid or alcohol functionality (from glyoxal), oligomers (from pyruvic acid and methylglyoxal), and additional organic acids were formed in experiments but not in controls or in standards containing mixtures of expected precursors and products (ESI-MS; Altieri et al., 2006; Carlton et al., 2007a; Altieri et al., 2007). We expect that oligomers and other large multifunctional products will also contribute SOA upon droplet evaporation.
As predicted by our model, glyoxal photooxidation yielded glyoxylic and oxalic acids; methylglyoxal photooxidation yielded pyruvic, acetic, formic, glyoxylic and oxalic acids. However, glyoxylic acid concentrations were insufficient to explain the majority of oxalic acid formation. The rapid increase in oxalic acid corresponds to the breakdown of larger multifunctional products, suggesting that these large products are some how involved in oxalic acid formation. Also, rapid formation of formic and acetic acids from methylglyoxal and formic acid from glyoxal was observed. Presumably these products form from direct nucleophilic attack. At higher acidity oxalic acid yields were somewhat lower. Acetic acid formation was observed in controls, but formation of oxalic acid and larger multifunctional compounds from these aldehyde precursors required the presence of hydroxyl radical (formed from H2O2 + UV).
We used time series data from glyoxal experiments, the initial reaction mechanism, and a commercially available equation solver (FACSIMILE) to validate and refine the glyoxal photooxidation aqueous chemical mechanism. Agreement between predictions and measurements of oxalic acid in the reaction vessel were much improved (from r2 = 0.001 to r2 > 0.8) after the glyoxal mechanism was refined (expanded) to include the role of large multifunctional compounds and direct formation of formic acid (Carlton et al., 2007a). (The complete aqueous phase mechanism is provided in Supporting Information, Atmos. Environ.)
The expanded aqueous glyoxal mechanism has now been used in a cloud parcel model and in a chemical transport model (CMAQ) through collaborations with Dr. Barbara Ervens and Dr. Annmarie Carlton (both at NOAA). The cloud parcel work is now in press in Geophysical Research Letters (Ervens et al., 2007). This model includes gas and aqueous phase reactions. The yield of SOA from isoprene (through cloud processing of isoprene oxidation products) varied from 0.4% to 40%, with higher NOx producing higher yields. The cloud parcel model did not include the contribution of oligomers formed from methylglyoxal. A future goal (beyond the scope of this project) is to incorporate organic cloud processing fully into the EPA CMAQ model. As a first step, a 4% SOA yield from glyoxal and from methylglyoxal (based on laboratory results and supported by the cloud parcel modeling) was used to model SOA formation through cloud processing in the eastern US for August 2004 (Carlton et al., submitted). Cloud processing increased particulate organic carbon estimates by as much as 5 μg/m3 at the surface. Agreement with aircraft measurements (August 14) was dramatically improved when cloud processing was included, especially agreement aloft. (The normalized mean bias was reduced from –60 to –10%; Carlton et al., submitted). Cloud processing helps to explain the “greater-than-predicted” organic carbon concentrations that have been measured by others in the free troposphere (Heald et al., 2005).
Our initially unexpected findings of oligomer formation have led us to conduct additional, unplanned research to better understand the composition and formation of these large products. We analyzed several samples from pyruvic acid and methylglyoxal reaction experiments by ultra high resolution ESI-FT-ICR-MS and ESI-MS-MS. This work provides strong evidence that oligomers form from aqueous photooxidation of methylglyoxal through acid-catalyzed estrification with a hydroxy acid, resulting in multiple additions of 72.02113 Da to the parent organic acid monomer. An expanded reaction mechanism has been proposed and is supported by ESI-MS-MS evidence. OM/OC, O:C, and H:C ratios are reported for high molecular weight products (Altieri et al., 2007). More work will be need to incorporate this mechanism into a kinetic model that is able to reproduce the concentrations of methylglyoxal photooxidation products observed in the reaction vessel.
Conclusions:This research provides strong evidence that oxalic acid, other organic acids, large multifunctional compounds, and oligomers form in the aqueous phase in the presence of hydroxyl radical under conditions found in atmospheric waters (clouds and aerosol water). This material will remain, at least in part, in the particle phase after cloud droplet evaporation, producing secondary organic aerosol (SOA) aloft. Isoprene, other alkenes and aromatics of biogenic and anthropogenic origin are precursors. Formation of SOA through cloud processing of isoprene appears to be enhanced at higher NOx concentrations because the formation of water-soluble carbonyl species in the gas phase is favored under these conditions (Ervens et al., 2007). Measurement of products in laboratory experiments has lead to an improved understanding of aqueous photooxidation mechanisms and improved kinetic models. When cloud processing was included in a chemical transport model, predicted particulate organic carbon concentrations were substantially greater at the ground and agreement with measurements was greatly improved, especially aloft. This work suggests that cloud processing is a substantial, previously unrecognized, contributor to SOA when conditions are favorable.
References:
Altieri, K. E., Carlton, A. G., Lim, H. J., Turpin, B. J., Seitzinger, S. (2006) Formation of oligomers in cloud-processing: Reactions of isoprene oxidation products. Environ. Sci. Technol., 40:4956-4960.
Altieri, K. E., Seitzinger, S. P., Carlton, A. G., Turpin, B. J., Klein, G. C., Marshall, A. G. (2007) Oligomers formed through in-cloud methylglyoxal reactions: Chemical composition, properties, and mechanisms investigated by ultra-high resolution FT-ICR Mass Spectrometry, Atmos. Environ., in press.
Blando, J. D. and Turpin, B. J. (2000) Secondary Organic Aerosol Formation in Cloud and Fog Droplets: A Literature Evaluation of Plausibility, Atmos. Environ. 34:1623-1632.
Carlton, A. G., Turpin, B. J., Lim, H. J., Altieri, K. E., and Seitzinger, S. (2006) Link between isoprene and SOA: Pyruvic acid oxidation yields low volatility organic acids in clouds. Geophys. Res. Let., 33, L06822, doi:10.1029/2005GL025374.
Carlton, A. C., Turpin, B. J., Altieri, K. E., Reff, A., Seitzinger, S., Lim, H. J., and Ervens, B. (2007a) Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments, Atmos. Environ. 41:7588-7602.
Carlton, A. C., Turpin, B. J., Altieri, K. E., Seitzinger, S. P., Mathur, R., Roselle, S. J., Weber, R. J. (2007b) In-cloud secondary organic aerosol (SOA): Air quality and climate implications, Science, submitted.
Crahan, K.K., Hegg, D., Covert, D.S., Jonsson, H. (2004), An exploration of aqueous oxalic acid production in the coastal marine atmosphere, Atmos. Environ., 23, 3757-3764.
Ervens, B., Feingold, G., Frost, G.J., Kreidenweis, S.M. (2004), A modeling study of aqueous production of dicarboxylic acids: 1. Chemical pathways and speciated organic mass production, J. Geophys. Res., 109, doi:10.1029/2003JD004387.
Ervens, B., Carlton, A. G., Turpin, B. J., Altieri, K. E., Kreidenweis, S. M., Feingold, G. (2007) Secondary organic aerosol yields from cloud-processing of isoprene oxidation products, Geophys. Res. Lett., in press.
Heald, C.L., Jacob, D.J., Park, R.J., Russell, L.M., Heubert, B.J., Seinfeld, J.H., Liao, H., Webber, R.J. (2005), A large organic aerosol source in the free troposphere missing from current models, Geophys. Res. Lett., 32, doi:10.1029/2005GL023831.
Lim, H.J., Carlton, A.G., Turpin, B.J. (2005), Isoprene forms secondary organic aerosol through cloud processing: model simulations, Environ.Sci.Technol., 39, 4441-4446.
Polidori, A., Turpin, B.J., Lim, H.J., Cabada, J.C., Subramanian, R., Robinson, A.L., Pandis, S.N. (2006) Local and regional secondary organic aerosol: Insights from a year of semi-continuous measurements at Pittsburgh. Aerosol Sci. Technol. 40: 861-872.
Sorooshian, A., Varutbangkul, V., Brechtel, F.J., Ervens, B., Feingold, G., Bahreini, R., Murphy, S.M., Holloway, J.S., Atlas, E.L., Buzorius, G., Jonsson, H., Flagan, R.C., Seinfeld, J.H. (2006) Oxalic acid in clear and cloudy atmospheres: Analysis of data from ICARTT 2004. Journal of Geophysical Research - Atmospheres, 111, D23S45.
Journal Articles on this Report: 5 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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Carlton AG, Turpin BJ, Altieri KE, Seitzinger S, Reff A, Lim H-J, Ervens B. Atmospheric oxalic acid and SOA production from glyoxal: results of aqueous photooxidation experiments. Atmospheric Environment 2007;41(35):7588-7602. |
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
2006 Progress Report
Original Abstract