Cloud Processing of Gases and Aerosols in a Regional Air Quality Model (AURAMS): Evaluation Against Aircraft Data

Clouds play an active role in the processing and cycling of chemicals in the atmosphere. Gases and aerosols can enter cloud droplets through absorption/condensation (of soluble gases) and activation and impact scavenging (of aerosol particles). Once inside the cloud droplets these tracers can dissolve, dissociate, and undergo chemical reactions. It is believed that aqueous phase chemistry in cloud is the largest contributor to sulphate aerosol production. Some of the aqueousphase tracers will be removed from the atmosphere when precipitation forms and reaches the ground. However, the majority of clouds are non-precipitating, and upon cloud dissipation and evaporation, the tracers, physically and chemically altered, will be released back to the atmosphere. Updrafts and downdrafts in convective clouds are also efficient ways of redistributing atmospheric tracers in the vertical. It is therefore important to represent these cloud-related physical and chemical processes when modelling the transport and transformation of atmospheric chemical tracers, particularly aerosols.