Box model studies of the secondary organic aerosol formation under different HC/NOx conditions using the subset of the Master Chemical Mechanism for α-pinene oxidation

Abstract

A subset of a near-explicit Master Chemical Mechanism (v3.1) describing α-pinene oxidation (976 reactions and 331 compounds) coupled with a gas/particle absorptive partitioning model is used as a benchmark for the study of secondary organic aerosol (SOA) formation within a box model under atmospheric relevant conditions of averaged HC/NOx ratios between 0.18 and 8.43 (ppbvC/ppbv). Results from the detailed mechanism for α-pinene oxidation show that total SOA mass increases as the HC/NOx ratio increases within the studied range. The mass of peroxynitrates and the nitrates in the aerosol phase increases with increasing HC/NOx ratio, despite decreases in the total (gas plus aerosol) mass of these species, because of increases in mass of organic peroxides and acids in these conditions. The fractional composition of aerosol mass indicates organic peroxides and acids dominate at high HC/NOx ratios and peroxynitrates and nitrates dominate at low HC/NOx ratios. In addition, 28 out of 149 condensable products are identified as important compounds for SOA formation. Of the organic nitrates, only two contribute consistently to organic aerosol mass. Organic peroxide and acid mass in the aerosol phase is distributed ever a larger number of species. The 28 species identified here are suitable targets for future laboratory and field analysis of organic aerosols and are recommended for use in future mechanism reduction work. Copyright 2008 by the American Geophysical Union.