Grantee Research Project Results
2010 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, 2009 through October 31,2010
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 are developing a quantitative understanding of the kinetics, products, and mechanisms of secondary organic aerosol (SOA) formation from the photooxidation of aromatic hydrocarbons, and will 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 the first year of this program, 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 (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, 1997, study to determine a 2-formylcinnamaldehyde formation yield of 56%. Combined with other previously observed and quantified products, we can now account for ~92% of naphthalene reaction products under conditions where the NO2 concentration is greater than ~60 ppbv.
In the second year of this project, these gas-phase chemistry studies continued. The formation yields of glyoxal were measured from the OH radical-initiated reactions of naphthalene, 1-methylnaphthalene, 1,4-dimethylnaphthalene, acenaphthene and acenaphthylene, using solid phase microextraction (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, of 2-acetylbenzaldehyde from 1-methylnaphthalene and of 1,2-diacetylbenzene from 1,4-dimethylnaphthelene 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.
Commencing in year two and continuing into year three of this project, 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. SPME fibers were used for sample collection, and our data show that 2-formylcinnamaldehyde is formed in the absence (as well as in the presence) of NOx, indicating that the OH-naphthalene adduct + O2 reaction forms 2-formylcinnamaldehyde. Based on a 2-formylcinnamaldehyde yield at ppm levels of NO2, the 2-formylcinnamaldehyde yields at 0.1 ppm NOx and in the absence of NOx are 43% and ~20%, respectively. In the absence of NO, RO2 + RO2 and RO2 +HO2 radical reactions will dominate and a lower yield of 2-formylcinnamaldehyde is expected if 2-formylcinnamaldehyde is formed from the alkoxy radical. Our data then suggest that the 2-formylcinnamaldehyde formation yield is not too dissimilar from the reactions of the OH-naphthalene adducts with O2 and NO2. Also commencing in the second year and continuing into the third year of this project, the 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 formation yields of CH3C(O)CH=CHC(O)CH3 (mainly the cis-isomer) from OH + 2,5-dimethylfuran are 24 ± 3% in the presence of NO and 34 ± 4% in the absence of NO, and the API-MS analyses showed the additional formation of molecular weight 114 and 128 products, these being attributed to CH3C(O)CH=CHCOOH and CH3C(O)OCH=CHC(O)CH3, respectively. Analogous measurements are in progress for furan, 2- and 3-methylfuran and 2,3-dimethylfuran, with preliminary yield of CH3C(O)C(CH3)=CHCHO from OH + 2,3-dimehtylfuran in the presence of NO of ~10%. Using API-MS to monitor the 1,4-unsaturated dicarbonyls, the concentration-time dependence of the 1,4-unsaturated dicarbonyls have 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. Data analysis is in progress.
We have investigated formation of cresols from the OH + m-xylene and OH + p-cymene reactions to assess the importance of dealkylation (e.g., OH + m-xylene ® cresol + CH3). We see no evidence for cresol formation from either reaction (<1% of any cresol isomer from m-xylene and <2% of any cresol isomer from p-cymene). Formation of 4-methylacetophenone, a product expected after H-atom abstraction from the CH(CH3)2 group, was observed from p-cymene, and a yield of 14.8 ± 3.2% measured. Inclusion of other products arising after H-atom abstraction from the methyl and isopropyl substituent groups indicates that H-atom abstraction from these substituent groups accounts for 20 ± 4% of the overall OH radical reaction for p-cymene. The formation yields of dimethylnitronaphthalenes are being measured from the reactions of OH radicals with 1,7- and 2,7-dimethylnaphthalene (chosen because the 1,7- and 2,7-dimethylnitronaphthalenes are the dominant dimethylnitronaphthalenes during daytime in the atmosphere) as a function of NO2 concentration. We have completed experiments with 1,7-dimehtylnaphthalene, and the yield of 1,7-dimethylnitronaphthalenes is ~0.2% with a dependence on the NO2 concentration similar to that for naphthalene.
These gas-phase studies provide information on the products formed, and their yields, which is critical for chemical mechanisms of the atmospheric photooxidation of aromatic hydrocarbons and subsequent SOA formation.
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. NO2 can compete with O2 in reactions of the aromatic-OH adduct, and NO, NO2, RO2•, and HO2 radicals can all compete with each other in reactions with RO2• radicals. Furthermore, it appears that oligomers are a major component of SOA and the reactions that lead to their formation are complex and influenced by the specific mix of gas-phase products, RH, and acidity. In years two and three 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 currently is 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 of 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. SOA yields/reacted unsaturated 1,4-dicarbonyl were estimated from the measurements and it was observed that under all conditions the SOA yields from the m-xylene reactions were much larger (often by more than an order of magnitude) than could be explained by the products of unsaturated 1,4-dicarbonyl reactions. This indicates that the products formed from reactions of unsaturated 1,4-dicarbonyls were not by themselves responsible for SOA formation from m-xylene. This conclusion was supported by real-time and temperature-programmed thermal desorption particle mass spectra, which showed that the SOA formed from the m-xylene and methylfuran reactions had very different compositions. One potential explanation is that methylglyoxal and/or phenols, which are not formed in the methylfuran reactions, or some unknown products, are important for SOA formation, either alone or through oligomer-forming reactions with the products of the unsaturated 1,4-dicarbonyl reactions. This possibility was explored by adding methyglyoxal and phenols separately to a chamber containing the products of methyfuran reactions, but no additional SOA was formed.
It often has been reported that SOA formation from the reactions of aromatics is much higher in the absence of NO, with the usual explanation being that under these conditions organic peroxides are formed that contribute significantly to SOA formation. This hypothesis has never been tested, so in year three we measured the mass of organic peroxides in SOA formed from OH-initiated reactions of toluene, m-xylene, p-xylene, 1,3,5-trimethylbenzene, and benzaldehyde in the presence and absence of NO using a method we developed previously. Results were quite consistent, with SOA mass fractions of organic peroxides of 5.7–6.8% for reactions in the presence of NO and 16.4–21.3% in the absence of NO. These results provide the first direct evidence that organic peroxides contribute significantly to SOA formation from aromatic oxidation, especially in the absence of NO, but that other components are also important.
A variety of studies also have been carried out in year three on the effects of RH, acidity, and NH3 on SOA formation, with data analysis ongoing. SOA formation from the reactions of benzaldehyde (a toluene-OH radical reaction product) with OH radicals in the absence of NOx has also been explored, with HPLC analyses carried out to identify SOA products. 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 the apparently unusual reaction pathways by which they are formed.
Almost all of the work originally proposed is completed and/or under way, with considerable progress made toward meeting goals. This is especially the case in the areas of gas-phase product identification, quantification, and kinetics. SOA studies have focused primarily on effects of conditions on yields from aromatics and related methylfurans, and a variety of methods for product identification have been employed, including mass spectrometry, spectrophotometry, and functional group and elemental analysis.
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 aromatic hydrocarbons, and to study the kinetics and products of OH radical-initiated reactions of unsaturated 1,4-dicarbonyls. We also 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, RH, and NH3, as well as the role of unsaturated 1,4-dicarbonyls, methylgloxal, glyoxal, and phenolic compounds in SOA formation using a suite of analytical techniques. Professor Ziemann recently moved his laboratory across the street from its former location into Fawcett Laboratory, where the Atkinson/Arey laboratories are located. The labs now are integrated fully so that joint studies of SOA formation using real-time particle and gas mass spectrometric analysis can be carried out. The focus will be on product identification, then on quantification and heterogeneous kinetics.Journal Articles on this Report : 7 Displayed | Download in RIS Format
Other project views: | All 34 publications | 16 publications in selected types | All 16 journal articles |
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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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Aschmann SM, Arey J, Atkinson R. Extent of H-atom abstraction from OH + p-cymene and upper limits to the formation of cresols from OH + m-xylene and OH + p-cymene. Atmospheric Environment 2010;44(32):3970-3975. |
R833752 (2010) R833752 (2011) R833752 (Final) |
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Aschmann SM, Nishino N, Arey J, Atkinson R. Kinetics of the reactions of OH radicals with 2-and 3-methylfuran, 2,3-and 2,5-dimethylfuran, and E-and Z-3-hexene-2,5-dione, and products of OH + 2,5-dimethylfuran. Environmental Science & Technology 2011;45(5):1859-1865. |
R833752 (2010) R833752 (2011) R833752 (Final) |
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Nishino N, Atkinson R, Arey J. Formation of nitro products from the gas-phase OH radical-initiated reactions of toluene, naphthalene, and biphenyl: effect of NO2 concentration. Environmental Science & Technology 2008;42(24):9203-9209. |
R833752 (2010) 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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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) |
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Nishino N, Arey J, Atkinson R. Formation yields of glyoxal and methyglyoxal from the gas-phase OH radical-initiated reactions of toluene, xylenes, and trimethylbenzenes as a function of NO2 concentration. The Journal of Physical Chemistry A 2010;114(37):10140-10147. |
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,
http://www.envisci.ucr.edu/faculty/atkinson.html,
http://www.envisci.ucr.edu/faculty/ziemann.html
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.