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

• Molecular characteristics of organic acids in PM10 samples in the coastal region of Southeastern China
• Seasonal and diurnal variations of organic acids in ambient PM10
• Molecular distribution of organic acids in primary emissions
• Organic acid source identification by diagnostic ratios and principal component analysis

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 547 ng m− 3 at the coastal urban sites and between 163 and 245 ng m− 3 at off-island sites. These levels were much lower than those reported in Chinese megacities (668–1568 ng m− 3) and slightly lower than those in Jeju Island, Korea (464–744 ng m− 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.

Higher values of C3/C4, C6/C9 and Ph/C9 ratios observed in summer are mainly attributed to the higher solar radiation and temperature, while the seasonal variations of C18:1/C18:0 were overwhelmed by fresh input of C18:1 in summer.Figure optionsDownload as PowerPoint slide