n-Alkanoic monocarboxylic acid concentrations in urban and rural aerosols: Seasonal dependence and major sources

We report new data on the abundance and distribution of n-monocarboxylic acids (n-MCAs) in fine- and coarse-mode aerosols in rural and urban areas of Sweden, and determine their possible sources. Overall, C-6-C-16 n-MCAs accounted for similar to 0.5-1.2% of the total PM10 (particulate matter 75%), with the exception of wintertime samples from a rural site, where C-6-C-11 acids accounted for 65% of the total C-6-C-16 n-MCA mass. Positive matrix factorization analysis revealed four major sources of n-MCAs: traffic emissions, wood combustion, microbial activity, and a fourth factor that was dominated by semi-volatile n-MCAs. Traffic emissions were important in the urban environment in both seasons and at the rural site during winters, and were a major source of C-9-C-11 acids. Wood combustion was a significant source at urban sites during the winter and also to some extent at the rural site in both seasons. This is consistent with the use of wood for domestic heating but may also be related to meat cooking. Thus, during the winter, traffic, wood combustion and microbial activity were all important sources in the urban environment, while traffic was the dominant source at the rural site. During the summer, there was considerable day-to-day variation in n-MCA concentrations but microbial activity was the dominant source. The semi-volatile low molecular weight C-6-C-8 acids accounted for a small (similar to 5-10%) fraction of the total mass of n-MCAs. This factor is unlikely to be linked to a single source and its influence instead reflects the partitioning of these compounds between the gas and particle phases. This would explain their greater contribution during the winter. (C) 2014 Elsevier B.V. All rights reserved.