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Simulating the Degree of Oxidation in Atmospheric Organic Particles

Simon, Heather, Bhave, Prakash V.
Environmental Science & Technology 2012 v.46 no.1 pp. 331-339
aerosols, air quality, carbon, emissions, model validation, models, oxidation, oxygen, particulates, summer, urban areas, winter, United States
Modeled ratios of organic mass to organic carbon (OM/OC) and oxygen to carbon (nO/nC) in organic particulate matter are presented across the US for the first time and evaluated extensively against ambient measurements. The base model configuration systematically underestimates OM/OC ratios during winter and summer months. Model performance is greatly improved by applying source-specific OM/OC ratios to the primary organic aerosol (POA) emissions and incorporating a new parametrization to simulate oxidative aging of POA in the atmosphere. These model improvements enable simulation of urban-scale gradients in OM/OC with values in urban areas as much as 0.4 lower than in the surrounding regions. Modeled OM/OC and nO/nC ratios in January range from 1.4 to 2.0 and 0.2 to 0.6, respectively. In July, modeled OM/OC and nO/nC ratios range from 1.4 to 2.2 and 0.2 to 0.8, respectively. Improved model performance during winter is attributed entirely to our application of source-specific OM/OC ratios to the inventory. During summer, our treatment of oxidative aging also contributes to improved performance. Advancements described in this paper are codified in the latest public release of the Community Multiscale Air Quality model, CMAQv5.0.