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Title
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Cloud processing of secondary organic aerosol from isoprene and methacrolein photooxidation
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Author
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Abstract
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| Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpretation of the Earth's changing energy budget. The present study explores experimentally the impacts of water condensation-evaporation events, mimicking processes occurring, in atmospheric clouds, on the molecular composition of secondary organic aerosol (SOA) from the photooxidation of methacrolein. A range of on and off-line mass spectrometry techniques were used to obtain a detailed chemical characterization of SOA formed in control experiments in dry conditions, in triphasic experiments simulating gas-particle-cloud droplet interactions (starting from dry conditions and from 60% relative humidity (RH)), and in bulk aqueous-phase experiments. We observed that cloud events trigger fast SOA formation accompanied by evaporative losses. These evaporative losses decreased SOA concentration in the simulation chamber by 25-32% upon RH increase, while aqueous SOA was found to be metastable and slowly evaporated after cloud dissipation. In the simulation chamber, SOA composition measured with a high-resolution time-of flight aerosol mass spectrometer, did not change during cloud events compared with high RH conditions (RH > 80%). In all experiments, off-line mass spectrometry techniques emphasize the critical role of 2-methylglyceric acid as a major product of isoprene chemistry, as an important contributor to the total SOA mass (15-20%) and as a key building block of oligomers found in the particulate phase. Interestingly, the comparison between the series of oligomers obtained from experiments performed under different conditions show a markedly different reactivity. In particular, long reaction times at high RH seem to create the conditions for aqueous-phase processing to occur in a more efficient manner than during two relatively short cloud events. |
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Language
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English
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Source (journal)
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The journal of physical chemistry : A : molecules, spectroscopy, kinetics, environment and general theory. - Washington, D.C., 1997, currens
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Publication
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Washington, D.C.
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2017
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ISSN
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1089-5639
[print]
1520-5215
[online]
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DOI
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10.1021/ACS.JPCA.7B05933
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Volume/pages
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121
:40
(2017)
, p. 7641-7654
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ISI
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000413131300023
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Pubmed ID
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28902512
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Full text (Publisher's DOI)
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