Global modeling of organic aerosol: the importance of reactive nitrogen (NO sub(x) and NO sub(3))

Reactive nitrogen compounds, specifically NO sub(x) and NO sub(3), likely influence global organic aerosol levels. To assess these interactions, GEOS-Chem, a chemical transport model, is updated to include improved biogenic emissions (following MEGAN v2.1/2.04), a new organic aerosol tracer lumping scheme, aerosol from nitrate radical (NO sub(3)) oxidation of isoprene, and NO sub(x)-dependent monoterpene and sesquiterpene aerosol yields. As a result of significant nighttime terpene emissions, fast reaction of monoterpenes with the nitrate radical, and relatively high aerosol yields from NO sub(3) oxidation, biogenic hydrocarbon-NO sub(3) reactions are expected to be a major contributor to surface level aerosol concentrations in anthropogenically influenced areas such as the United States. By including aerosol from nitrate radical oxidation in GEOS-Chem, terpene (monoterpene + sesquiterpene) aerosol approximately doubles and isoprene aerosol is enhanced by 30 to 40% in the Southeast United States. In terms of the global budget of organic aerosol, however, aerosol from nitrate radical oxidation is somewhat minor (slightly more than 3 Tg/yr) due to the relatively high volatility of organic-NO sub(3) oxidation products in the yield parameterization. Globally, 69 to 88 Tg/yr of organic aerosol is predicted to be produced annually, of which 14-15 Tg/yr is from oxidation of monoterpenes and sesquiterpenes and 8-9 Tg/yr from isoprene.