AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Global Transformation and Fate of SOA: Implications of Low Volatility and Gas Phase Fragmentation Reactions
MANISHKUMAR SHRIVASTAVA, Richard Easter, Xiaohong Liu, Alla Zelenyuk, Singh Balwinder, Kai Zhang, Po-Lun Ma, Duli Chand, Steven Ghan, Jose-Luis Jimenez, Qi Zhang, Jerome Fast, Philip Rasch, Petri Tiitta, Pacific Northwest National Laboratory
Abstract Number: 431 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) are large contributors to fine particle loadings and radiative forcing, but are often represented crudely in global models. We have implemented three new detailed SOA treatments within the Community Atmosphere Model version 5 (CAM5) that allow us to compare the semi-volatile versus non-volatile SOA treatments (based on some of the latest experimental findings), and to investigate the effects of gas-phase fragmentation reactions. The new treatments also track SOA from biomass burning and biofuel, fossil-fuel, and biogenic sources. For semi-volatile SOA treatments, fragmentation reactions decrease the simulated annual global SOA burden from 7.5 Tg to 1.8 Tg. For the non-volatile SOA treatment with fragmentation, the burden is 3.1 Tg. Larger differences between non-volatile and semi-volatile SOA (upto a factor of 5) exist in areas of continental outflow over the oceans. According to comparisons with observations from global surface Aerosol Mass Spectrometer measurements and the US IMPROVE network measurements, the FragNVSOA treatment, which treats SOA as non-volatile and includes gas-phase fragmentation reactions, agrees best at rural locations. All three revised treatments show much better agreement with aircraft measurements of organic aerosols (OA) over the North American Arctic and sub-Arctic in spring and summer, compared to the standard CAM5 formulation. This is mainly due to the oxidation of SOA precursor gases from biomass burning, not included in standard CAM5, and long-range transport of biomass burning OA at high altitudes. The non-volatile and semi-volatile configurations with fragmentation predict the direct radiative forcing of SOA as -0.5 W m-2 and -0.26 W m-2 respectively, at top of the atmosphere, which are higher than previously estimated by most models, but in reasonable agreement with a recent constrained modeling study.