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Atmosphere 2011, 2(4), 567-616;

Cloud Processing of Gases and Aerosols in Air Quality Modeling

Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
Author to whom correspondence should be addressed.
Received: 10 June 2011 / Revised: 15 September 2011 / Accepted: 16 September 2011 / Published: 10 October 2011
(This article belongs to the Special Issue Air Pollution Modeling: Reviews of Science Process Algorithms)
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The representations of cloud processing of gases and aerosols in some of the current state-of-the-art regional air quality models in North America and Europe are reviewed. Key processes reviewed include aerosol activation (or nucleation scavenging of aerosols), aqueous-phase chemistry, and wet deposition/removal of atmospheric tracers. It was found that models vary considerably in the parameterizations or algorithms used in representing these processes. As an emerging area of research, the current understanding of the uptake of water soluble organics by cloud droplets and the potential aqueous-phase reaction pathways leading to the atmospheric secondary organic aerosol (SOA) formation is also reviewed. Sensitivity tests using the AURAMS model have been conducted in order to assess the impact on modeled regional particulate matter (PM) from: (1) the different aerosol activation schemes, (2) the different below-cloud particle scavenging algorithms, and (3) the inclusion of cloud processing of water soluble organics as a potential pathway for the formation of atmospheric SOA. It was found that the modeled droplet number concentrations and ambient PM size distributions were strongly affected by the use of different aerosol activation schemes. The impact on the modeled average ambient PM mass concentration was found to be limited in terms of averaged PM2.5 concentration (~a few percents) but more significant in terms of PM1.0 (up to 10 percents). The modeled ambient PM was found to be moderately sensitive to the below-cloud particle scavenging algorithms, with relative differences up to 10% and 20% in terms of PM2.5 and PM10, respectively, when using the two different algorithms for the scavenging coefficient (Λ) corresponding to the lower and upper bounds in the parameterization for Λ. The model simulation with the additional cloud uptake and processing of water-soluble organic gases was shown to improve the evaluation statistics for modeled PM2.5 OA compared to the IMPROVE network data, and it was demonstrated that the cloud processing of water-soluble organics can indeed be an important mechanism in addition to the traditional secondary organic gas uptake to the particle organic phase. View Full-Text
Keywords: cloud processes; aerosol activation; aqueous-phase chemistry; sulphate; secondary organic aerosol; cloud-aerosol interaction; wet deposition cloud processes; aerosol activation; aqueous-phase chemistry; sulphate; secondary organic aerosol; cloud-aerosol interaction; wet deposition
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Gong, W.; Stroud, C.; Zhang, L. Cloud Processing of Gases and Aerosols in Air Quality Modeling. Atmosphere 2011, 2, 567-616.

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