Atmospheric Chemistry and Physics (Feb 2013)
Evaluation of factors controlling global secondary organic aerosol production from cloud processes
Abstract
Secondary organic aerosols (SOA) exert a significant influence on ambient air quality and regional climate. Recent field, laboratorial and modeling studies have confirmed that in-cloud processes contribute to a large fraction of SOA production with large space-time heterogeneity. This study evaluates the key factors that govern the production of cloud-process SOA (SOA<sub>cld</sub>) on a global scale based on the GFDL coupled chemistry-climate model AM3 in which full cloud chemistry is employed. The association between SOA<sub>cld</sub> production rate and six factors (i.e., liquid water content (LWC), total carbon chemical loss rate (TC<sub>loss</sub>), temperature, VOC/NO<sub>x</sub>, OH, and O<sub>3</sub>) is examined. We find that LWC alone determines the spatial pattern of SOA<sub>cld</sub> production, particularly over the tropical, subtropical and temperate forest regions, and is strongly correlated with SOA<sub>cld</sub> production. TC<sub>loss</sub> ranks the second and mainly represents the seasonal variability of vegetation growth. Other individual factors are essentially uncorrelated spatiotemporally to SOA<sub>cld</sub> production. We find that the rate of SOA<sub>cld</sub> production is simultaneously determined by both LWC and TC<sub>loss</sub>, but responds linearly to LWC and nonlinearly (or concavely) to TC<sub>loss</sub>. A parameterization based on LWC and TC<sub>loss</sub> can capture well the spatial and temporal variability of the process-based SOA<sub>cld</sub> formation (<i>R</i><sup>2</sup> = 0.5) and can be easily applied to global three dimensional models to represent the SOA production from cloud processes.