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Abstract: The object of this study was to investigate the chemical compositions of PM2.5 and its correlations with visibility and meteorological parameters in peri-urban of Xiamen, a southeast coastal city, China. PM2.5 samples were collected monthly from June 2009 to May 2010. The major compositions of PM2.5 such as water soluble inorganic ions (WSIIs) (F−, Cl−, NO2 −, NO3 −, SO4 2−, Na+, K+, NH4 +, Mg2+, and Ca2+) and carbonaceous fractions (organic carbon (OC) and elemental carbon (EC)) were determined to estimate their contribution to light extinction coefficients. The results showed that the annual average concentration of PM2.5 was 86.16μg/m3, with monthly individual values ranging from 58.61μg/m3 to 109.39μg/m3. The correlation analysis showed that PM2.5 had higher correlations with visibility (r =−0.89) and relative humidity (r =−0.75), while there was no apparent correlation between PM2.5 and wind speed. Water soluble inorganic ions and carbonaceous fractions were the major compositions of PM2.5 accounting for 28.7% and 20.7% of the total PM2.5 mass, respectively. NO3 −, SO4 2−, and NH4 + were the major water soluble inorganic ions, accounting for 22.7%, 44.4%, and 17.7% of the total water soluble inorganic ions (TWSIIs), respectively. The average concentrations of secondary organic carbon (SOC) in summer, autumn, winter, and spring in Xiamen were 4.16, 6.48, 13.00 and 8.01μg/m3, which accounted for 43.4%, 45.5%, 54.6% and 58.8% of OC, respectively. The annual average light extinction coefficient of PM2.5 ((b ext)fine particle) was 214.3Mm−1, which was estimated by the IMPROVE algorithm. The average percentage contributions to (b ext)fine particle were 39.5% for organic mass, 31.4% for ammonium sulfate, 15.3% ammonium nitrate, and 13.9% for elemental carbon. [Copyright &y& Elsevier]