A review of chemistry-aerosol treatments in CAM5 and implementation of a sectional aerosol package with comprehensive SOA formation

Description

Virtually all properties of atmospheric aerosols and clouds depend strongly on aerosol size distribution, composition, and mixing state. These microphysical characteristics underlie the major role of aerosols in radiative forcing of climate. Current interactive chemistry-aerosol modules in CAM5 include a “bulk” approach based on the Model of Ozone and Related Tracers (MOZART) that simulates mass concentrations of externally mixed aerosols as well as a “modal” treatment (MAM) that predicts mass/number concentrations and mode radii of externally and internally mixed aerosols. Both existing treatments do not resolve the detailed aerosol size distributions, and they oversimplify the formation of secondary organic aerosols (SOAs) that make up a significant portion of the global aerosol burden. A wide range for the estimates of global SOA formation (12–70 Tg/year) leads to a significant uncertainty in the spatial and temporal distributions of atmospheric aerosols. In this study, we examine the simulated regional ozone levels with resolutions from CAM5/MOZART, compare aerosol concentrations and optical depth from MOZART and MAM, and reveal cloud properties associated with different aerosol modules. We also introduce our ongoing effort to implement a sectional aerosol package into CAM5 that integrates MOZART gas chemistry with MADRID aerosol microphysics (Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution). This new chemistry-aerosol package includes SOA formation from two anthropogenic and six biogenic organic precursors. Preliminary results from CAM5/SECT will be presented.