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Exploring matrix effects on photochemistry of organic aerosols

Lignell, Hanna and Hinks, Mallory L. and Nizkorodov, Sergey A. (2014) Exploring matrix effects on photochemistry of organic aerosols. Proceedings of the National Academy of Sciences of the United States of America, 111 (38). pp. 13780-13785. ISSN 0027-8424. PMCID PMC4183274.

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This work explores the effect of the environment on the rate of photolysis of 2,4-dinitrophenol (24-DNP), an important environmental toxin. In stark contrast to the slow photolysis of 24-DNP in an aqueous solution, the photolysis rate is increased by more than an order of magnitude for 24-DNP dissolved in 1-octanol or embedded in secondary organic material (SOM) produced by ozonolysis of α-pinene. Lowering the temperature decreased the photolysis rate of 24-DNP in SOM much more significantly than that of 24-DNP in octanol, with effective activation energies of 53 kJ/mol and 12 kJ/mol, respectively. We discuss the possibility that the increasing viscosity of the SOM matrix constrains the molecular motion, thereby suppressing the hydrogen atom transfer reaction to the photo-excited 24-DNP. This is, to our knowledge, the first report of a significant effect of the matrix, and possibly viscosity, on the rate of an atmospheric photochemical reaction within SOM. It suggests that rates of photochemical processes in organic aerosols will depend on both relative humidity and temperature and thus altitude. The results further suggest that photochemistry in SOM may play a key role in transformations of atmospheric organics. For example, 24-DNP and other nitro-aromatic compounds should readily photodegrade in organic particulate matter, which has important consequences for predicting their environmental fates and impacts.

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Lignell, Hanna0000-0001-7049-1659
Additional Information:Copyright © 2014 National Academy of Sciences. Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved August 1, 2014 (received for review November 25, 2013). Dr. Scott Epstein is thanked for many helpful comments and acknowledged for the design of the solid-state photolysis setup. Dr. Carla Kidd is warmly acknowledged for fruitful discussions. Funding from National Science Foundation Grants AGS-1227579 (to S.A.N.) and CHE-0909227 (to H.L. and M.L.H.) are acknowledged. H.L. also acknowledges the Finnish Cultural Foundation and Magnus Ehrnrooth Foundation for financial support. Author contributions: H.L. and S.A.N. designed research; H.L. and M.L.H. performed research; H.L. and M.L.H. analyzed data; and H.L., M.L.H., and S.A.N. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Funding AgencyGrant Number
Finnish Cultural FoundationUNSPECIFIED
Magnus Ehrnrooth FoundationUNSPECIFIED
Subject Keywords:aerosol aging; particle viscosity; organic photochemistry
Issue or Number:38
PubMed Central ID:PMC4183274
Record Number:CaltechAUTHORS:20140911-222335839
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Official Citation:Hanna Lignell, Mallory L. Hinks, and Sergey A. Nizkorodov Exploring matrix effects on photochemistry of organic aerosols PNAS 2014 111 (38) 13780-13785; published ahead of print September 8, 2014, doi:10.1073/pnas.1322106111
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49630
Deposited By: George Porter
Deposited On:12 Sep 2014 16:33
Last Modified:09 Mar 2020 13:19

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