PNNL

Abstract

Secondary organic aerosols (SOA) are large contributors to fine particle mass and number concentration and interact with clouds and radiation. Several processes affect the formation, and removal of SOA in the atmosphere. For computational efficiency, global models use simplified SOA treatments, which often do not capture the dynamics of SOA formation. Here we test more complex SOA treatments within the global Energy Exascale Earth System Model (E3SM) to investigate how simulated SOA spatial distributions respond to some of these processes. We evaluate model predictions with a suite of observations that span the globe and the full troposphere. Simulations indicate that both, a strong production (achieved here by multigenerational aging of SOA precursors) and a strong sink of SOA (especially in the mid-upper troposphere, achieved here by adding particle-phase photolysis) are needed to reproduce the vertical distribution of organic aerosol (OA) measured during several aircraft field campaigns; without this sink, the simulated mid-upper tropospheric OA is too large. Our results show that variations in SOA chemistry formulations change SOA wet removal lifetime by a factor of 3. In all the SOA chemistry formulations tested here, an efficient chemical sink i.e. particle-phase photolysis, was needed to reproduce the aircraft measurements of OA at high altitudes. Globally, SOA removal rates by photolysis are equal to the wet removal sink, and photolysis decreases SOA lifetimes from 10 days to ~3 days. Differences in SOA treatments greatly affect the SOA direct radiative effect, which ranges from -0.65 W m-2 to -2 W m-2.