MEASUREMENT AND SPECIATION OF GAS AND PARTICULATE PHASE ORGANIC ACIDITY IN AN URBAN-ENVIRONMENT .2. SPECIATION

In the previous paper we discussed the sampling and analytical techniq ues used to measure the concentrations of gas and particulate phase or ganic acids. This paper presents the results of a field study conducte d in Philadelphia, Pennsylvania, during the summer of 1992, to investi gate the chemistry and origins of gas and particulate phase organic ac ids. The concentrations of formic acid and most of the particulate pha se organic acids were found to be significantly higher during the day than at night. Organic acids constituted 5.5% of the particulate fine mass (PM(2.5)); sulfates, ammonium, and elemental carbon were larger c omponents of particulate fine mass, constituting 40, 15, and 9%, respe ctively. Dicarboxylic acids and even-carbon monocarboxylic acids were found to account for a large fraction of particulate weak acidity; odd -carbon monocarboxylic acids accounted for a very small fraction. The pronounced even-carbon preference of the monocarboxylic acid distribut ion suggests a biogenic origin. To investigate the origin of gas and p articulate phase organic acids with regard to other species measured a s part of the same field study, specific rotation factor analysis (SRF A) was applied to the daytime and nighttime concentrations of several species over the study period. During the daytime, four sources (trans port, local combustion, biogenic, and photochemical) accounted for 92- 99% of the particulate phase and 60-75% of the gas phase organic acids . At night, 68-87% of gas and particulate organic acids were contribut ed by four significant sources (transport, daytime concentration relat ed, local combustion, and biogenic).