Global Transformation and Fate of SOAs: Implications of Low Volatility SOA and Gas-Phase Fragmentation Reactions
Secondary organic aerosols (SOAs) are often the dominant components of fine aerosols at many locations globally, but they are also the least understood. Their chemistry and properties are complex and poorly known, but they may play an important role in affecting cloud-aerosol interactions. SOA particles are created by complex multiscale interactions among human activities (fossil-fuel burning), biomass burning, and terrestrial biosphere and marine biogenic emissions that are linked by physical and chemical atmospheric processes. Although SOAs are large contributors to fine particle amounts and radiative forcing, they often are represented crudely in global models. For the first time, research led by U.S. Department of Energy researchers at Pacific Northwest National Laboratory replaced the previous crude SOA treatments with much more advanced treatments in a global climate model. The new treatments account for chemical reactions in the atmosphere that are both sources and sinks of SOA precursor gases (multigenerational aging), low “effective volatility” of SOA particles due to aging processes in the particle-phase, and “missing” semi-volatile/intermediate volatility precursors from global biomass burning and fossil-fuel sources. The new treatments caused large increases in simulated aerosol amounts, lifetimes, and direct radiative forcing compared to previous global modeling treatments and dramatically improved agreement with a suite of surface-based, aircraft, and satellite organic aerosol measurements, especially in regions affected by biomass burning emissions. The ratio of their revised non-volatile SOA to previous semi-volatile SOA burden varied by a factor of 2 to 5. Their new model treatments also largely increased loadings and lifetimes of SOA particles corresponding to continental outflow over marine environments, where cloud reflectivity (albedo) is highly sensitive to cloud seed (cloud condensation nuclei or CCN) concentrations. Their work shows that new and advanced aerosol model treatments are expected to change the radiative forcing of aerosols simulated by current generation global climate models. These findings will have large potential impacts on our understanding of aerosol-cloud-radiative forcing interactions.
Shrivastava, M., R. C. Easter, X. Liu, A. Zelenyuk, B. Singh, K. Zhang, P.-L. Ma, D. Chand, S. Ghan, J. L. Jimenez, Q. Zhang, J. Fast, P. J. Rasch, and P. Tiitta. 2015. “Global Transformation and Fate of SOA: Implications of Low Volatility SOA and Gas-Phase Fragmentation Reactions,” Journal of Geophysical Research-Atmospheres, DOI: 10.1002/2014JD022563.