A microphysical parameterization of aqSOA and sulfate formation in clouds

Abstract

AbstractSulfate and secondary organic aerosol (cloud aqSOA) can be chemically formed in cloud water. Model implementation of these processes represents a computational burden due to the large number of microphysical and chemical parameters. Chemical mechanisms have been condensed by reducing the number of chemical parameters. Here an alternative is presented to reduce the number of microphysical parameters (number of cloud droplet size classes). In‐cloud mass formation is surface and volume dependent due to surface‐limited oxidant uptake and/or size‐dependent pH. Box and parcel model simulations show that using the effective cloud droplet diameter (proportional to total volume‐to‐surface ratio) reproduces sulfate and aqSOA formation rates within ≤30% as compared to full droplet distributions; other single diameters lead to much greater deviations. This single‐class approach reduces computing time significantly and can be included in models when total liquid water content and effective diameter are available.