Semivolatile behavior of dicarboxylic acids and other polar organic species at a rural background site (Nylsvley, RSA)

In this study aerosol samples from the South African savanna were analyzed for their polar organic constituents. Samples were collected with a front/b ack-up filter tandem system of quartz fiber filters (dual filter strategy). In all samples (n = 15) dicarboxylic acids and a variety of phthalates, al dehydes and monocarboxylic acids were observed. Oxalic acid was the dominat ing compound with an average amount of 79.2 ng m(-3) on the front filter an d 11.3 ng m(-3) on the back-up filter. The presence of significant concentr ations of dicarboxylic acids on the back-up filter was rather unexpected. T here are two possible sources to explain the presence of individual compoun ds on the back-up filter - particle penetration through the front filter or adsorption of compound parts from the gas phase. Interpretation of the dat a indicates that the dicarboxylic acid concentrations on the back-up filter s appear to be caused by the adsorption of gaseous organic species. Dicarbo xylic acids semivolatilic behavior is evident with this results. This concl usion refutes the commonly held view that dicarboxylic acids in the atmosph ere were associated with the aerosol phase only. Additionally, it was found that the distribution of dicarboxylic acids between the gas and particle p hase in the atmosphere is not only dependent on their vapor pressures. The actual gas phase concentration appears to be more determined by the chemica l properties of the particles than by pure physical influences. Surprisingl y, malonic acid exhibits an anomaly, as it does not show a semivolatile ten dency. (C) 2001 Elsevier Science Ltd. All rights reserved.