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The signature of aqSOA: Aerosol modification by secondary organic aerosol formation in the aqueous phase
Barbara Ervens (1,2), Annmarie Carlton (3)
(1) CIRES, (2) NOAA/ESRL CSD, (3) Dept. of Environmental Sciences, Rutgers University, NJ
Organics comprise a large fraction of atmospheric particulate matter. The major fraction of this organic aerosol mass is formed by physical or chemical processes in the atmosphere (secondary organic aerosol, SOA). Traditional approaches describe SOA formation by condensation of low-volatility or semivolatile gas phase species on preexisting aerosol particles.
The formation of secondary organic aerosol formation in cloud and aerosol water (aqSOA) has attracted great attention over the past years. While it has been recognized that aqSOA formation might significantly contribute to the total SOA budget in humid and cloudy regions, the modification of specific aerosol properties, such as size distribution (‘droplet mode’), oxygenation state (O/C ratio), light-absorbing properties and vertical distribution has not been explored. We apply different models in order to predict typical ‘signatures of aqSOA’ due to organic mass addition in clouds and aqueous aerosol.
(i) A parcel model allows implementing detailed multiphase chemistry and explicitly tracking the modification of aerosol distributions by addition of newly aqSOA mass within wet aerosol and cloud droplets. Since usually aqSOA compounds are more highly oxidized (higher O/C ratio) and water-soluble than those of traditional (gas)SOA, processed aerosol size distributions exhibit not only a distinct modification in their size distribution but also in their size-resolved hygroscopicity.
(ii) While such chemical and microphysical detail is not available in larger scale models, such models give information on the three-dimensional aerosol distribution. Using an air quality model (CMAQ), we show that the vertical profile of aerosol is clearly modified in the presence of clouds if aqSOA formation in included.
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