How much complexity is needed in global model organic aerosol simulations?

Abstract:

The skill in simulating the global atmospheric distribution and fate of organic aerosols (OA) of thirty-one global chemistry/transport and general circulation models of various complexities will be presented. Significant differences between models are identified in the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used, the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over an order of magnitude exists in the modeled vertical distribution of OA concentrations pointing to uncertainties in the parameterization of the semi-volatile character of OA and its temperature dependence, as well as OA long-range transport.

Fine aerosol organic carbon (OC) and OA observations from continuous monitoring networks and individual field campaigns have been used for model evaluation. Τhe combined model/measurements analysis suggests the existence of increased OA levels during summer due to biogenic SOA formation over large areas of the USA that can be of the same order of magnitude as the POA, even at urban locations, and contribute to the observed urban seasonal pattern. The global models are able to simulate the high secondary character of OA observed in the atmosphere as a result of SOA formation and of POA aging, although, the amount of OA present in the atmosphere remains largely underestimated.

The models skill with increasing model complexity with regard to OC or OA mass concentration will be presented and thoroughly discussed. This work is part of AeroCom phase II.