An ion chromatographic analysis of water-soluble, short-chain organic acids in ambient particulate matter

Abstract

Recent studies have shown that the inclusion of water-soluble short-chain (WSSC) organic acids in source apportionment using positive matrix factorization (PMF) resulted in an improvement in the model's ability to resolve sources, and in understanding secondary particle formation. In the United States, numerous network samplers are operational. Quartz-fibre filters for thermal optical carbon analysis have been collected over a period of years as a part of these sampling campaigns on a routine basis. However, only a small portion of these filters are used for the carbon analysis. Thus, there is the potential to utilize these samples to enhance organic speciation for subsequent use in source apportionment. In this work, an ion-chromatographic method was developed to identify and quantify the WSSC organic acids present in fine particulate matter (PM2.5). Samples collected to measure the concentrations of particles (PM2.5) in south-western (Stockton) and northern (Potsdam) New York, USA from November 2002 to June 2004 were used in this study. Acetic, formic, propionic, oxalic, and malonic acids were successfully identified. The identified species accounted for 5–15% of the organic matter mass and thus enhance the knowledge of atmospheric organic-matter constituents. Oxalic acid was the most abundant species at Potsdam and Stockton with median concentrations of 17.71 ng m−3 and 92 ng m−3, respectively. Acetic and formic acids were present in Potsdam at median concentrations of 12.54 ng m−3 and 14.48 ng m−3, while at Stockton they were present at 57.58 ng m−3 and 51.54 ng m−3, respectively. The median concentration values for all acids at Stockton were higher than Potsdam. These observations are consistent with a study conducted in a semi-urban location, Schenectady, New York. At both sites, propionic and malonic acids were found in much lower concentrations when compared with the other acids. The concentration time series of various acids and seasonal variations in individual acids are discussed. The co-variance of acetic and formic acids is also outlined.