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_cld) on a global scale based on the GFDL coupled chemistry-climate model AM3 in which full cloud chemistry is employed. The association between SOA_cld production rate and six factors (i.e., liquid water content (LWC), total carbon chemical loss rate (TC_loss), temperature, VOC/NO_x, OH, and O₃) is examined. We find that LWC alone determines the spatial pattern of SOA_cld production, particularly over the tropical, subtropical and temperate forest regions, and is strongly correlated with SOA_cld production. TC_loss ranks the second and mainly represents the seasonal variability of vegetation growth. Other individual factors are essentially uncorrelated spatiotemporally to SOA_cld production. We find that the rate of SOA_cld production is simultaneously determined by both LWC and TC_loss, but responds linearly to LWC and nonlinearly (or concavely) to TC_loss. A parameterization based on LWC and TC_loss can capture well the spatial and temporal variability of the process-based SOA_cld formation (R² = 0.5) and can be easily applied to global three dimensional models to represent the SOA production from cloud processes.