Grantee Research Project Results
2008 Progress Report: Chemistry of Secondary Organic Aerosol Formation from the Oxidation of Aromatic Hydrocarbons
EPA Grant Number: R833752Title: Chemistry of Secondary Organic Aerosol Formation from the Oxidation of Aromatic Hydrocarbons
Investigators: Ziemann, Paul J. , Arey, Janet , Atkinson, Roger
Institution: University of California - Riverside
EPA Project Officer: Chung, Serena
Project Period: October 1, 2007 through September 30, 2010 (Extended to March 31, 2012)
Project Period Covered by this Report: October 1, 2007 through September 30,2008
Project Amount: $514,464
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:
In this project, we plan to develop a quantitative understanding of the kinetics, products, and mechanisms of secondary organic aerosol (SOA) formation from the photooxidation of aromatic hydrocarbons, and to provide this information to the scientific community in a form that can be readily incorporated into SOA modules used in air quality models for predicting atmospheric organic PM2.5 concentrations. These types of models are widely used to evaluate the potential effects of aerosols on global climate, air pollution and visibility, and human health, which are all important problems confronting society.Progress Summary:
Work focused on studies of gas-phase and SOA products formed from OH radical-initiated reactions of aromatic compounds and on instrument development. Most of the originally planned environmental chamber studies are underway and the flow tube reactor, a critical instrument for this project, has been constructed but not yet characterized.
Environmental chamber experiments were carried out to identify and quantify dicarbonyl products formed from reactions of toluene, o-, m- and p-xylene and 1,2,3-, 1,2,4- and 1,3,5-trimethylbenzene. Gas-phase products were collected using denuders coated with XAD resin and O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine to derivatize carbonyl-containing products for GC/MS analysis. The 1,2-dicarbonyls glyoxal, methylglyoxal and biacetyl were observed, as were 8 of 9 possible unsaturated 1,4-dicarbonyl co-products. Compared to their potential co-product 1,2-dicarbonyls, unsaturated 1,4-diketones had similar formation yields, whereas all but one unsaturated 1,4-dialdehyde and keto-aldehyde had lower yields. These results provide new product yields from aromatic reactions that can be used as inputs to atmospheric models.
2-Formylcinnamaldehyde is a major product of the OH radical-initiated reaction of naphthalene, the atmospherically most abundant polycyclic aromatic hydrocarbon, whose oxidation has been suggested as a possible source of SOA in urban atmospheres. The photolysis rate of 2-formylcinnamaldehyde was measured by monitoring its time dependent signal during the naphthalene-OH reaction using atmospheric pressure ionization mass spectrometry (API-MS). Results were used with those from our earlier study to determine a formation yield of 56%. Combined with other previously observed and quantified products, we can account for ~92% of reaction products under conditions where the NO2 concentration is greater than ~60 ppbv.
An atmospheric pressure, laminar flow reactor was constructed for studies of SOA formation so experimental conditions such as reactant concentrations, residence time, humidity, and NOx can be easily varied. The reactor is a ~30 cm diameter x 180 cm long glass tube with 4 blacklights mounted on one side used to initiate OH radical formation by photolysis. Reaction products are sampled through a movable on-axis tube to allow residence times ranging from ~10 s to 30 min. Also for this project, an ion trap mass spectrometer (ITMS) was modified for on-line gas analysis. The design employs a home-built cryotrap to collect VOC precursor and reaction products, prior to evaporation into the ITMS. Detection limits are ~ 5 ppbv/5 min collection.
Environmental chamber studies of SOA formation from reactions of toluene and m-xylene with OH/NOx produced little SOA, so studies focused on OH/low NOx reactions that form more SOA. For example, SOA formed from the m-xylene reaction was analyzed using a thermal desorption particle beam mass spectrometer (TDPBMS) in real-time and in a temperature-programmed thermal desorption mode. Mass spectra indicate the presence of stable molecular products and oligomers whose composition continues to evolve with time even in the absence of OH radicals. SOA desorbed between ~40-120oC, indicative of vapor pressures at 25oC of ~10-6-10-11 torr corresponding to products ranging from semi-volatile to non-volatile. Because mass spectra indicated the presence of ring-retaining products, similar experiments were conducted with benzaldehyde, an aromatic product of the toluene reaction. Measurements showed ~20% of SOA mass was organic peroxides, most likely acylperoxyhemiacetals formed in the particle-phase reaction of peroxybenzoic acid and benzaldehyde, which then slowly decomposed.
The experimental data obtained in this project will include reaction rate constants, product branching ratios, and yields of gas-phase and particle-phase products and SOA from the OH radical-initiated reactions of aromatic hydrocarbons. These data can be used by atmospheric modelers as inputs into detailed chemical mechanisms, which in turn can be used directly or after condensation in urban and regional airshed computer models.
Future Activities:
Yields of dicarbonyls from reactions of aromatic hydrocarbons as a function of NO2 concentration will be measured, and an API-MS will be used to investigate the kinetics and products of OH radical-initiated reactions of unsaturated 1,4-dicarbonyls. The flow tube reactor will be characterized and then it and environmental chambers will be used for studies of SOA formation from OH radical-inititated reactions of toluene, m- and p-xylene, and 1,3,5-trimethylbenzene in the presence and absence of NOx. The focus will initially be on product identification, then on quantification and heterogeneous kinetics.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 34 publications | 16 publications in selected types | All 16 journal articles |
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Type | Citation | ||
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Arey J, Obermeyer G, Aschmann SM, Chattopadhyay S, Cusick RD, Atkinson R. Dicarbonyl products of the OH radical-initiated reaction of a series of aromatic hydrocarbons. Environmental Science & Technology 2009;43(3):683-689. |
R833752 (2008) R833752 (2009) R833752 (2010) R833752 (2011) R833752 (Final) |
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Nishino N, Arey J, Atkinson R. Formation and reactions of 2-formylcinnamaldehyde in the OH radical-initiated reaction of naphthalene. Environmental Science & Technology 2009;43(5):1349-1353. |
R833752 (2008) R833752 (2009) R833752 (2010) R833752 (2011) R833752 (Final) |
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Supplemental Keywords:
absorption, chemicals, environmental chemistry, global climate, oxidants, particulates, PAHs, regional and climate models, toxics, tropospheric, VOCRelevant Websites:
http://www.envisci.ucr.edu/faculty/arey.html Exit
http://www.envisci.ucr.edu/faculty/atkinson.html Exit
http://www.envisci.ucr.edu/faculty/ziemann.html Exit
Progress 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.