Size-segregated chemistry of particulate dicarboxylic acids in the Arctic atmosphere

Gas-particle interactions of low-molecular-weight dicarboxylic acids were s tudied at a coastal Arctic site during the summer. Size segregated measurem ents with a Berner low-pressure impactor displayed up to four modes for ion ic compounds: an Aitken mode, an accumulation mode, and two supermicron mod es. The lower supermicron mode was ascribed to sea-salt, whereas the upper mode consisted mostly of species associated with continental particles. All four modes could be identified for oxalic acid, with the lower supermicron mode being the dominant. Malonic acid displayed a supermicron mode but was not found in the submicron size range. Succinic acid had an accumulation m ode and, in a few samples, a supermicron mode. Glutaric acid displayed some times and accumulation mode, sometimes a supermicron mode, and occasionally both. The most probable formation pathway for submicron oxalic and glutari c acid was condensation from the gas phase, even though production in cloud droplets cannot be ruled out either. A slightly different formation pathwa y may have been important for submicron succinic acid production. Supermicr on oxalic acid was probably formed by condensation from the gas-phase, by h eterogeneous reactions occurring on the surface of pre-existing sea-salt an d continental particles, or in cloud droplets. A larger mass median diamete r for supermicron malonic and glutaric acid might be indicative of liquid-p hase production in aqueous sea-salt particles. Evidence on possibly substan tial sampling artifacts related to measuring dicarboxylic acids using filte rs were also obtained. (C) 1999 Elsevier Science Ltd. All rights reserved.