Nitrate formation in the atmosphere: Experimental and theoretical constraints

This thesis considers the effect of nitrogen oxides (NO x) on organic peroxy radicals (RO2) in atmospheric chemistry. Two broad areas are addressed. First, the theoretical model of the RO2 + NO reaction system is developed to understand the role of key intermediates (ROONO) on RO2 + NO reaction products. Special emphasis is placed on understanding organic nitrate (RONO2) formation, especially for large carbon number compounds (C# ≥ 10). This model is also applied to inorganic nitrate (HONO2) and the HOONO intermediate formation from OH + NO2 and HO2 + NO reactions. Second, experiments on Secondary Organic Aerosol (SOA) formation for the limonene + ozone system are carried out to test for sensitivity to NO x levels and to measure organic nitrate production at high NOx condition.; Major findings of this thesis include: (a) RONO2 formation has a high-pressure, high-carbon number limit of around 0.4, determined by the formation branching ratio of the two ROONO intermediates (cis- and trans-ROONO); (b) trans-ROONO and trans-HOONO conversion to nitrate has significant effects on reaction dynamics of these systems (i.e. including small HONO 2 formation from HO2 + NO); (c) SOA formation from limonene + ozone reaction is very efficient, possibly making limonene the most important biogenic SOA precursor. The NOx effect on the absolute SOA formation efficiency is modest, however, there is a dramatic and unexpected NOx effect on the SOA formation kinetics, which we attribute to substantial sensitivity of heterogeneous ozone uptake coefficients on unsaturated organic particles during SOA formation.