Grantee Research Project Results
2009 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: November 1, 2008 through October 31,2009
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:
In year one of this project, environmental chamber experiments of gas-phase chemistry 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 (PFBHA) 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. In addition, 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). 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. 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.
In year two of this project, these gas-phase chemistry studies continued. Using Solid Phase MicroExtraction (SPME) fibers for sample collection, 2-formylcinnamaldehyde formation from OH + naphthalene has been investigated in the absence of NOx (using O3 + alkene to generate OH radicals) and in the presence of NOx at 0.1 and 1 ppm NOx. Although data analysis is currently underway, 2-formylcinnamaldehyde is formed in the absence of NOx, indicating that the OH-naphthalene adduct + O2 reaction forms 2-formylcinnamaldehyde. The formation yields of glyoxal also have been measured from the OH radical-initiated reactions of naphthalene, 1-methylnaphthalene, 1,4-dimethylnaphthalene, acenaphthene and acenaphthylene, using SPME fibers pre-coated with PFBHA for collection of glyoxal and GC-FID for analysis. In the presence of NOx, glyoxal was observed as a first-generation product from the above aromatics, with yields of 5%, 3%, 2%, 10-15% and <2%, respectively, with a yield from naphthalene in the absence of NOx of 3%. Second-generation formation was obvious from the 1-methylnaphthalene, 1,4-dimethylnaphthalene and acenaphthene reactions. Simultaneous measurements of phthaldialdehyde from naphthalene, 2-acetylbenzaldehyde from 1-methylnaphthalene and 1,2-diacetylbenzene from 1,4-dimethylnaphthalene suggest that these aromatic dicarbonyls are co-products to glyoxal.
The formation yields of glyoxal and methylglyoxal have been measured from the gas-phase OH radical-initiated reactions of toluene, o-, m- and p-xylene, and 1,2,3-, 1,2,4- and 1,3,5-trimethylbenzene as a function of the NO2 concentration [(0.1-4) ppm]. Glyoxal and methylglyoxal were collected onto SPME fibers pre-coated with PFBHA and analyzed as their oximes by GC-FID. The glyoxal and methylglyoxal yields generally decrease with increasing NO2 concentration. However, for formation of glyoxal from 1,2,3-trimethylbenzene and of glyoxal and methylglyoxal from 1,2,4-trimethylbenzene, the yields were independent of the NO2 concentration within the experimental errors. These data allow, by a very short extrapolation, glyoxal and methylglyoxal yields appropriate for atmospheric conditions.
Formation of unsaturated 1,4-dicarbonyls (and other products) from the OH radical-initiated reactions of furans (furan, 2- and 3-methylfuran and 2,3- and 2,5-dimethylfuran) are being investigated using denuders (see above), gas chromatography and API-MS. These studies are valuable for understanding the chemistry of aromatic reactions because the unsaturated 1,4-dicarbonyls formed from these furans are the same as those formed from aromatics, but are formed in higher yields and with fewer co-products so they can be used more easily to investigate the subsequent kinetics and products of the 1,4-unsaturated dicarbonyl reactions. To date, we have shown that furan forms HC(O)CH=CHCHO, 2-methylfuran forms CH3C(O)CH=CHCHO, 3-methylfuran forms HC(O)C(CH3)=CHCHO, 2,3-dimethylfuran forms CH3C(O)C(CH3)=CHCHO, and 2,5-dimethylfuran forms CH3C(O)CH=CHC(O)CH3. The CH3C(O)CH=CHC(O)CH3 formation yields are 24% in the presence of NO and 34% in the absence of NO, and yield measurements are in progress for the other furans. Using API-MS to monitor the 1,4-unsaturated dicarbonyls, the concentration-time dependence of the 1,4-unsaturated dicarbonyls is being measured from the five furans available, allowing the rate constant ratio k(OH + unsaturated dicarbonyl)/k(OH + furan) to be derived (this assumes that photolysis is negligible, which is the case for CH3C(O)CH=CHC(O)CH3 and will be checked for the others. To date, preliminary data have been obtained for formation of CH3C(O)CH=CHC(O)CH3 from OH + 2,5-dimethylfuran and CH3C(O)C(CH3)=CHCHO from OH + 2,3-dimethylfuran.
The approach to SOA studies has built on our growing understanding of gas-phase chemistry and has sought to determine the specific gas-phase reaction products and conditions that lead to SOA formation. The chemistry is complicated because products of OH radical-initiated reactions of aromatics are influenced by concentrations of NO, NO2, RO2• and HO2 radicals, and by RH. NO2 can compete with O2 in reactions of the aromatic-OH adduct, and NO, NO2, and RO2• and HO2 radicals can all compete with each other in reactions with RO2• radicals. Furthermore, it appears that oligomers are a major (if not sole) component of SOA and the reactions that lead to their formation are complex and influenced by the specific mix of gas-phase products and RH. In year two of this project, a large number of environmental chamber reactions were carried out to investigate the yields of SOA formed from OH radical-initiated reactions of m-xylene, 3-methylfuran, and 2-methylfuran under different NO, NO2, and RH regimes. It is currently known that four major classes of products are formed from aromatic reactions: aromatic aldehydes, 1,2-dicarbonyls and their unsaturated 1,4-dicarbonyl co-products, and phenolic compounds. The major products identified to date for the m-xylene reaction are (yields in parentheses) aromatic aldehydes (<10%), methylglyoxal (40%) and its unsaturated 1,4-dicarbonyl co-products 2-methyl-2-butene-dial (5-14%) and 4-oxo-pentenal (~12-34%), glyoxal (~6%) and its co-product (1-2%), and phenolic compounds (~10%). It has been thought that highly multifunctional, second-generation products formed by the reactions of the unsaturated 1,4-dicarbonyls with OH radicals might be significant contributors to SOA formation. To investigate this possibility, the yields SOA formed from the reactions of m-xylene were compared with those formed from similar reactions of 3-methylfuran and 2-methylfuran, which form 2-methyl-2-butene-dial and 4-oxo-pentenal in substantially higher yields (~83% and ~60%, respectively) than from the m-xylene reaction. It was observed that in under all conditions the SOA yields from the m-xylene reactions were much larger (often by more than an order of magnitude), indicating that the products formed from reactions of unsaturated 1,4-dicarbonyls were not by themselves responsible for SOA formation from m-xylene and that methylglyoxal and/or phenols (which are not formed in the furan reactions) are important in SOA formation, either alone or through oligomer-forming reactions with the products of the unsaturated 1,4-dicarbonyl reactions. Yields also tended to be higher under high NO2 conditions, suggesting a possible role for PAN-type products in SOA formation, and also at high RH, consistent with a possible role of water in oligomer formation (most likely through gem-diol reactions).
Work also continued from year one on SOA formation from the reactions of benzaldehyde (a toluene-OH radical reaction product) with OH radicals in the absence of NOx. HPLC analyses were carried out to identify SOA products, and although the products are clearly aromatic, they do not correspond to any that would be expected from known chemistry: benzoic acid, benzoyl peroxide, benzyl anhydride, or peroxybenzoic acid (the latter compound was synthesized while the other standards were commercially available). This is a fascinating result, and it is hoped that further study will identify these products and then the apparently unusual reaction pathways by which they are formed.
Much of the work originally proposed for years one and two is underway and considerable progress has been made toward meeting goals, especially in the areas of gas-phase product identification, quantification, and kinetics. SOA studies have focused primarily on effects of conditions on yields from m-xylene and related furans, so additional aromatics need to be investigated and future joint gas-particle studies are expected to provide more detailed information on SOA product identification, quantification, and kinetics.
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:
We will continue to investigate the formation of unsaturated 1,4-dicarbonyls from the OH radical-initiated reactions of furans, and to study the kinetics and products of OH radical-initiated reactions of unsaturated 1,4-dicarbonyls. We also will carry out further environmental chamber studies on SOA formation from m-xylene oxidation by adding methylgloxal and phenolic compounds to unsaturated 1,4-dicarbonyl reaction product mixtures formed from furan oxidation to determine which combination of components promote SOA formation. In the next few months Professor Ziemann will be permanently moving his laboratory across the street from its current location into Fawcett Laboratory, where the Atkinson/Arey laboratories are located. The labs will be fully integrated so that flow tube reactor and environmental chamber studies of SOA formation using real-time particle and gas mass spectrometric analysis can be carried out. Studies there will investigate SOA formation from OH radical-initiated reactions of toluene, m- and p-xylene, and 1,3,5-trimethylbenzene in the presence and absence of NOx. The focus will be on product identification, then on quantification and heterogeneous kinetics. Two presentations on the research carried out to date will be given at the American Association for Aerosol Research (AAAR) 2010 Specialty Conference on Air Pollution and Health in San Diego, California, in March 2010.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 34 publications | 16 publications in selected types | All 16 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
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) |
Exit Exit Exit |
|
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) |
Exit Exit Exit |
|
Nishino N, Arey J, Atkinson R. Yields of glyoxal and ring-cleavage co-products from the OH radical-initiated reactions of naphthalene and selected alkylnaphthalenes. Environmental Science & Technology 2009;43(22):8554-8560. |
R833752 (2009) R833752 (2010) R833752 (2011) R833752 (Final) |
Exit Exit Exit |
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.