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[Distribution of Oxalate in Atmospheric Aerosols and the Related Influencing Factors in Qingdao, During Winter and Spring].

A total of 119 total suspended particle (TSP) samples were collected in Qingdao from December 2012 to April 2013. Concentrations of oxalate in TSP were measured to investigate the distributional characteristics of oxalate and the related influencing factors, in winter and spring. The concentrations of oxalate in Qingdao aerosols were 31-370 ng·m-3 with an average of 104 ng·m-3 in winter, and 11-1926 ng·m-3 with an average of 400 ng·m-3 in spring, with a significant difference between the concentrations in the two seasons. Different weather conditions affected the distribution of oxalate in aerosols. The oxalate concentration in TSP was the highest in the hazy days, followed by that in the dusty days, while this concentration in foggy days was close to that in the clear days, and the lowest concentration of oxalate appeared in the rainy days. Oxalate in Qingdao aerosols exhibited a significant positive correlation with temperature and solar radiation, suggesting that the secondary production of oxalic acid via photochemical oxidation has an important contribution to the oxalate concentrations in aerosols. The mechanisms of secondary formation of oxalate in aerosols in winter and spring are possibly different, with the aqueous phase oxidation process predominating in winter and the gas-phase oxidation-driven process predominating in spring. The results of PMF source analysis also showed that the secondary formation is the main source of oxalate in Qingdao aerosol, and its contribution to oxalate production is nearly 45% in winter and 70% in spring. The concentration of oxalate in spring aerosol was significantly higher than that in winter aerosol, the main reason of which was that temperature and solar radiation in spring were significantly higher than those in winter, promoting the secondary formation of particulate oxalate.