Possible next-generation aerosol developments in the ACME global model

Abstract

Secondary organic aerosols (SOA) are large contributors to fine particle loadings and radiative forcing, but are often represented crudely in global models. Recently, we implemented some of the most sophisticated treatments of secondary organic aerosols (SOA) within the atmospheric component of the Community Earth System Model (CESM). These new treatments used a 2-D multigenerational aging framework and a modified form of the volatility basis-set approach to represent multigenerational chemistry and changes in volatility of gas-phase SOA precursors due to both functionalization (decreasing volatility due to adding of functional groups to the carbon chain) and fragmentation reactions (increasing volatility due to breaking of C-C bonds). While these comprehensive parameterizations are computationally expensive, they show large improvements in predicted horizontal and vertical distributions of SOA with respect to a suite of surface, satellite and aircraft measurements, in comparison to the standard Community Atmosphere Model (CAM). As a part of future directions that ACME consider, we suggest implemention of a reduced-tracer and more computationally efficient version of the new comprehensive SOA treatments within the ACME model, which would greatly improve simulated SOA loadings and associated radiative forcing. In addition, we would implement a nucleation mode within MAM to explicitly represent freshly nucleated particles and their growth from 1 to 10 nm including the role of low volatility organics during new particle formation. New treatments of organic aerosols related to biomass and biofuel burning are expected to have large impacts on simulated indirect forcing of aerosols, and could be investigated as a part of this new aerosol development work. We can also investigate the absorbing effects of brown carbon OA using our new treatments, since brown carbon is especially important in regions affected by biomass burning emissions. We also propose to include SOA formation due to aging of marine isoprene and terpene emissions (not currently included in most atmospheric aerosol models). This could have important climate consequences due to larger sensitivity of cloud albedo to CCN concentrations over remote marine locations.

Shrivastava_ACME_Future_Directions_Secondary_Organic_Aerosol.pdf