Seasonal variations and source identification of selected organic acids associated with PM10 in the coastal area of Southeastern China

Abstract

PM10 aerosols from the coastal area of Southeastern China were collected from April 2010 to March 2011 and were measured for C2–C10 dicarboxylic acids, phthalic acids (Ph) and five fatty acids (palmitic, stearic, oleic, linoleic and elaidic acids). For all sites and seasons, molecular distributions of diacids were always characterized by a predominance of oxalic acid (C2), with a relative abundance of 68–87%, followed by malonic acid (C3) and by either succinic acid (C4) or phthalic acid (Ph). This observed molecular composition was different from that in Chinese megacities where Ph was significantly higher than C3 and C4 diacids, which was likely due to the less intensive traffic emissions in the coastal area. Seasonal means of total diacids ranged between 394 and 547ngm−3 at the coastal urban sites and between 163 and 245ngm−3 at off-island sites. These levels were much lower than those reported in Chinese megacities (668–1568ngm−3) and slightly lower than those in Jeju Island, Korea (464–744ngm−3) but higher than those in marine and continental background locations. In all seasons, saturated fatty acids were significantly higher than unsaturated fatty acids due to their greater photochemical stabilities in the atmosphere. Most organic acids showed higher levels in spring and winter and lower levels in summer and fall, which was likely due to the influence of transport and meteorology. The diagnostic ratios of malonic acid to succinic acid (C3/C4), adipic acid to azelaic acid (C6/C9) and phthalic acid to azelaic acid (Ph/C9) were significantly higher in summer than in winter. These diagnostic ratios in the sampled ambient aerosols were completely different from those in primary emissions, suggesting the importance of photochemical production — especially in summer. The diurnal variations of diacids and fatty acid as well as the diagnostic ratios are associated with higher solar radiation and anthropogenic activities during the daytime. Principal component analysis results provide evidence that photochemical oxidation of unsaturated fatty acids and volatile organic compounds is the most important source of diacids. In this analysis, primary sources were found to be minor (traffic and food cooking) or non-existent (biomass burning and crustal dust). Components with high loadings of Ph and unsaturated fatty acids can be regarded as representative of primary traffic emissions.