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The AeroCom Evaluation and Intercomparison of Organic Aerosol in Global Models

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Atmospheric aerosols are important drivers of air quality and climate. The majority of fine aerosol material is non-reflective and contains large amounts of organic matter. A multi-institutional team, including U.S. Department of Energy researchers at Pacific Northwest National Laboratory, evaluated the current status of global modeling of organic aerosol (OA) in the troposphere and analyzed the differences between models and observations. They evaluated thirty-one global chemistry transport models and general circulation models in this intercomparison for the Aerosol Comparisons between Observations and Models (AeroCom) phase II. The team found more than one order of magnitude differences in the global atmospheric burden of simulated organic aerosol, with little evidence that more complex treatments designed to study human impacts on organic aerosol are more accurate than simpler representations. The complexity is needed in models in order to distinguish between anthropogenic and natural OA as needed for climate mitigation, and to calculate the impact of OA on climate accurately. Despite the increasing diversity between models since AeroCom phase I experiments, the models are now able to simulate the secondary nature of OA observed in the atmosphere as a result of secondary organic aerosol formation and primary organic aerosol aging, although the absolute amount of OA present in the atmosphere remains underestimated. Results from the aerosol models were adapted to a common format and stored in a data repository, where they can be easily accessed for comparison with compilations of measurements of organic aerosol concentration, mostly from Europe and the United States.

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