Chemical compositions and extinction coefficients of PM2.5 in peri-urban of Xiamen, China, during June 2009–May 2010

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−, SO42 −, 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 86.16 μg/m3, with monthly individual values ranging from 58.61 μg/m3 to 109.39 μg/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−, SO42 −, 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 8.01 μg/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 ((bext)fine particle) was 214.3 Mm− 1, which was estimated by the IMPROVE algorithm. The average percentage contributions to (bext)fine particle were 39.5% for organic mass, 31.4% for ammonium sulfate, 15.3% ammonium nitrate, and 13.9% for elemental carbon.

In this study, chemical compositions, concentration levels, temporal variations, sources, and extinction coefficients of PM2.5 were determined monthly in peri-urban of Xiamen from June 2009 to May 2010, while the relationships between the light extinction coefficients and aerosol chemical compositions were derived by using IMPROVE algorithm.As figure has shown, firstly, the mean concentrations of water soluble inorganic ions (F−, Cl−, NO2−, NO3−, SO42 −, Na+, NH4+, K+, Mg2 +, and Ca2 +), organic carbon (OC), and elemental carbon (EC) showed obvious temporal variations, the lowest concentrations of which occurred in summer and the highest values appeared in winter, while those in autumn and spring kept moderate; Secondly, the diagnostic ratios of OC/EC and NO3−/SO42 − indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Xiamen, which suggested that more attention should be paid to vehicle exhaust and coal consumption. Thirdly, the correlation coefficient (r = − 0.75) showed that light extinction coefficient had a good correlation with visibility, which was closely related to meteorological conditions and chemical compositions, particularly organic mass and sulfate. Therefore, the reduction of carbonaceous species and sulfate in PM2.5 could effectively improve the visibility of Xiamen.It is hoped that the results from this study would be helpful for visibility degradation control in the future, as well as to provide a baseline reference for regulatory action to improve air quality in the region.Figure optionsDownload as PowerPoint slideHighlights
► PM2.5, water soluble inorganic ions, and carbonaceous fractions were determined monthly.
► Light extinction coefficients of major chemical compositions in PM2.5 were estimated.
► Water soluble inorganic ions and carbonaceous fractions were the major compositions of PM2.5.
► Vehicle exhaust and coal consumption were the main sources of atmospheric pollutants.
► Organic mass and ammonium sulfate were the main contributors to extinction coefficients.