Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation
Measurements of the evolution of organic aerosol extinction cross sections (σ[subscript ext]) and subsaturated hygroscopicity upon heterogeneous OH oxidation are reported for two model compounds, squalane (a C30 saturated hydrocarbon) and azelaic acid (a C9 dicarboxylic acid). For both compounds, th...
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| Format: | Article |
| Language: | en_US |
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American Geophysical Union (AGU)
2013
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| Online Access: | http://hdl.handle.net/1721.1/77943 https://orcid.org/0000-0002-6275-521X https://orcid.org/0000-0003-1627-5618 |
| _version_ | 1826208971511300096 |
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| author | Cappa, Christopher D. Che, Daphne L. Kessler, Sean Herbert Kroll, Jesse Wilson, Kevin R. |
| author2 | Massachusetts Institute of Technology. Department of Chemical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Chemical Engineering Cappa, Christopher D. Che, Daphne L. Kessler, Sean Herbert Kroll, Jesse Wilson, Kevin R. |
| author_sort | Cappa, Christopher D. |
| collection | MIT |
| description | Measurements of the evolution of organic aerosol extinction cross sections (σ[subscript ext]) and subsaturated hygroscopicity upon heterogeneous OH oxidation are reported for two model compounds, squalane (a C30 saturated hydrocarbon) and azelaic acid (a C9 dicarboxylic acid). For both compounds, the σ[subscript ext] values at 532 nm increase substantially as the particles undergo oxidation, exhibiting a logarithmic increase with OH exposure. The increase in σ[subscript ext] correlates with both an increase in the particle oxygen to carbon (O:C) atomic ratio and density and a decrease in mean molecular weight. The measurements have been used to calculate the variation with oxidation of the mean polarizability, α, of the molecules comprising the particles. The absolute α values for the two systems are shown to be related through the variation in the particle chemical composition, specifically the relative abundances of C, O, and H atoms and the mean molecular weight. Unlike σ[subscript ext], it was found that the evolution of the particle hygroscopicity upon oxidation is quite different for the two model systems considered. Hygroscopicity was quantified by measuring γ[subscript ext], which is a single-parameter representation of hygroscopicity that describes the increase in extinction upon exposure of the particles to a high–relative humidity environment (here, 75% and 85% RH). For unoxidized squalane, γ[subscript ext] was zero and only increased slowly as the particles were oxidized by OH radicals. In contrast, γ[subscript ext] for azelaic acid increased rapidly upon exposure to OH, eventually reaching a plateau at high OH exposures. In general, γ[subscript ext] appears to vary sigmoidally with O:C, reaching a plateau at high O:C. |
| first_indexed | 2024-09-23T14:15:39Z |
| format | Article |
| id | mit-1721.1/77943 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T14:15:39Z |
| publishDate | 2013 |
| publisher | American Geophysical Union (AGU) |
| record_format | dspace |
| spelling | mit-1721.1/779432022-09-28T19:32:14Z Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation Cappa, Christopher D. Che, Daphne L. Kessler, Sean Herbert Kroll, Jesse Wilson, Kevin R. Massachusetts Institute of Technology. Department of Chemical Engineering Massachusetts Institute of Technology. Department of Civil and Environmental Engineering Kessler, Sean Herbert Kroll, Jesse Measurements of the evolution of organic aerosol extinction cross sections (σ[subscript ext]) and subsaturated hygroscopicity upon heterogeneous OH oxidation are reported for two model compounds, squalane (a C30 saturated hydrocarbon) and azelaic acid (a C9 dicarboxylic acid). For both compounds, the σ[subscript ext] values at 532 nm increase substantially as the particles undergo oxidation, exhibiting a logarithmic increase with OH exposure. The increase in σ[subscript ext] correlates with both an increase in the particle oxygen to carbon (O:C) atomic ratio and density and a decrease in mean molecular weight. The measurements have been used to calculate the variation with oxidation of the mean polarizability, α, of the molecules comprising the particles. The absolute α values for the two systems are shown to be related through the variation in the particle chemical composition, specifically the relative abundances of C, O, and H atoms and the mean molecular weight. Unlike σ[subscript ext], it was found that the evolution of the particle hygroscopicity upon oxidation is quite different for the two model systems considered. Hygroscopicity was quantified by measuring γ[subscript ext], which is a single-parameter representation of hygroscopicity that describes the increase in extinction upon exposure of the particles to a high–relative humidity environment (here, 75% and 85% RH). For unoxidized squalane, γ[subscript ext] was zero and only increased slowly as the particles were oxidized by OH radicals. In contrast, γ[subscript ext] for azelaic acid increased rapidly upon exposure to OH, eventually reaching a plateau at high OH exposures. In general, γ[subscript ext] appears to vary sigmoidally with O:C, reaching a plateau at high O:C. National Science Foundation (U.S.) (ATM‐0837913) United States. Dept. of Energy (Contract DE‐AC02‐05CH11231) 2013-03-19T20:31:22Z 2013-03-19T20:31:22Z 2011-08 2011-04 Article http://purl.org/eprint/type/JournalArticle 0148-0227 2156–2202 http://hdl.handle.net/1721.1/77943 Cappa, Christopher D. et al. “Variations in Organic Aerosol Optical and Hygroscopic Properties Upon Heterogeneous OH Oxidation.” Journal of Geophysical Research 116.D15 (2011). ©2011 John Wiley & Sons, Inc. https://orcid.org/0000-0002-6275-521X https://orcid.org/0000-0003-1627-5618 en_US http://dx.doi.org/10.1029/2011jd015918 Journal of Geophysical Research. Atmospheres Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Geophysical Union (AGU) Other University Web Domain |
| spellingShingle | Cappa, Christopher D. Che, Daphne L. Kessler, Sean Herbert Kroll, Jesse Wilson, Kevin R. Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title_full | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title_fullStr | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title_full_unstemmed | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title_short | Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation |
| title_sort | variations in organic aerosol optical and hygroscopic properties upon heterogeneous oh oxidation |
| url | http://hdl.handle.net/1721.1/77943 https://orcid.org/0000-0002-6275-521X https://orcid.org/0000-0003-1627-5618 |
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