Seasonal differences in formation processes of oxidized organic aerosol near Houston, TX

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dc.citation.firstpage9641en_US
dc.citation.journalTitleAtmospheric Chemistry and Physicsen_US
dc.citation.lastpage9661en_US
dc.citation.volumeNumber19en_US
dc.contributor.authorDai, Qilien_US
dc.contributor.authorSchulze, Benjamin C.en_US
dc.contributor.authorBi, Xiaohuien_US
dc.contributor.authorBui, Alexander A.T.en_US
dc.contributor.authorGuo, Fangzhouen_US
dc.contributor.authorWallace, Henry W.en_US
dc.contributor.authorSanchez, Nancy P.en_US
dc.contributor.authorFlynn, James H.en_US
dc.contributor.authorLefer, Barry L.en_US
dc.contributor.authorFeng, Yinchangen_US
dc.contributor.authorGriffin, Robert J.en_US
dc.date.accessioned2019-11-14T17:52:21Zen_US
dc.date.available2019-11-14T17:52:21Zen_US
dc.date.issued2019en_US
dc.description.abstractSubmicron aerosol was measured to the southwest of Houston, Texas, during winter and summer 2014 to investigate its seasonal variability. Data from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) indicated that organic aerosol (OA) was the largest component of nonrefractory submicron particulate matter (NR-PM1) (on average, 38 % ± 13 % and 47 % ± 18 % of the NR-PM1 mass loading in winter and summer, respectively). Positive matrix factorization (PMF) analysis of the OA mass spectra demonstrated that two classes of oxygenated OA (less- and more-oxidized OOA, LO and MO) together dominated OA mass in summer (77 %) and accounted for 39 % of OA mass in winter. The fraction of LO-OOA (out of total OOA) is higher in summer (70 %) than in winter (44 %). Secondary aerosols (sulfate + nitrate + ammonium + OOA) accounted for ∼76 % and 88 % of NR-PM1 mass in winter and summer, respectively, indicating NR-PM1 mass was driven mostly by secondary aerosol formation regardless of the season. The mass loadings and diurnal patterns of these secondary aerosols show a clear winter–summer contrast. Organic nitrate (ON) concentrations were estimated using the NO+x ratio method, with contributions of 31 %–66 % and 9 %–17 % to OA during winter and summer, respectively. The estimated ON in summer strongly correlated with LO-OOA (r=0.73) and was enhanced at nighttime. The relative importance of aqueous-phase chemistry and photochemistry in processing OOA was investigated by examining the relationship of aerosol liquid water content (LWC) and the sum of ozone (O3) and nitrogen dioxide (NO2) (Ox = O3+NO2) with LO-OOA and MO-OOA. The processing mechanism of LO-OOA apparently was related to relative humidity (RH). In periods of RH < 80 %, aqueous-phase chemistry likely played an important role in the formation of wintertime LO-OOA, whereas photochemistry promoted the formation of summertime LO-OOA. For periods of high RH > 80 %, these effects were opposite those of low-RH periods. Both photochemistry and aqueous-phase processing appear to facilitate increases in MO-OOA concentration except during periods of high LWC, which is likely a result of wet removal during periods of light rain or a negative impact on its formation rate. The nighttime increases in MO-OOA during winter and summer were 0.013 and 0.01 µg MO-OOA per µg of LWC, respectively. The increase in LO-OOA was larger than that for MO-OOA, with increase rates of 0.033 and 0.055 µg LO-OOA per µg of LWC at night during winter and summer, respectively. On average, the mass concentration of LO-OOA in summer was elevated by nearly 1.2 µg m−3 for a ∼20 µg change in LWC, which was accompanied by a 40 ppb change in Ox.en_US
dc.identifier.citationDai, Qili, Schulze, Benjamin C., Bi, Xiaohui, et al.. "Seasonal differences in formation processes of oxidized organic aerosol near Houston, TX." <i>Atmospheric Chemistry and Physics,</i> 19, (2019) Copernicus Publications: 9641-9661. https://doi.org/10.5194/acp-19-9641-2019.en_US
dc.identifier.digitalacp-19-9641-2019en_US
dc.identifier.doihttps://doi.org/10.5194/acp-19-9641-2019en_US
dc.identifier.urihttps://hdl.handle.net/1911/107679en_US
dc.language.isoengen_US
dc.publisherCopernicus Publicationsen_US
dc.rightsThis work is distributed under the Creative Commons Attribution 4.0 License.en_US
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en_US
dc.titleSeasonal differences in formation processes of oxidized organic aerosol near Houston, TXen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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