Heterogeneous Reaction of Alkylamines on Dicarboxylic Acids Relevant to Secondary Organic Aerosol Formation

Secondary organic aerosols (SOA) are derived from non- and semivolatile oxidation products of volatile organic compounds (VOCs), and are suggested to cause adverse effects on human health, visibility, and climate. Organic acids are often found in SOAs, and the acid-base neutralization of these species by low molecular weight amines may result in the formation of stable low volatility aminium salt products contributing to the growth of SOAs and even alteration of the aerosol properties. Moreover, both laboratory and field studies suggest that atmospheric amines may exist as aminium salts following neutralization reactions with acidic species; however, the mechanisms involved in these processes are still uncertain. In order to understand the mechanisms entailed in the growth of SOAs, the uptake of gaseous dimethylamine (DMA) and trimethylamine (TMA) on solid phase succinic acid and adipic acid was investigated by employing a laminar fast flow reactor coupled to an ion drift chemical ionization mass spectrometer (ID-CIMS). The heterogeneous uptake of amines on each acid was rapid and governed primarily by the steric effects of each amine and the acidity of each acid. The results show that acid-base reactions between organic acids and atmospheric amines could contribute to the formation of aminium carboxylate salts and in turn the growth of SOAs