Correlation of Atmospheric Light Extinction with Chemical Composition of Aerosols in Arid of NW China

【摘要】：Atmospheric visibility can directly reflect the quality of air. In this study, We measured water-soluble ions(WSIs), organic and element carbon(OC and EC) in PM_(2.5) aerosols from August 2017 to August 2018 in the south of Urumqi. The IMPROVE formula is employed, which can reconstruct the PM_(2.5) chemical components and light extinction well. The results show that SO_4~(2-), NO_3~-, and NH_4~+ are the primary WSIs, accounting for 7.32%～84.12% of PM_(2.5) mass. Total carbon(TC=OC+EC) accounts for 12.12% of PM_(2.5) mass on average, and OC/EC 2 indicates the formation of secondary organic carbon(SOC). The level of SO_4~(2-), NO_3~-,and NH_4~+ in low visibility are much higher than those in high visibility, and relative humidity(RH) play key role in reducing visibility. In winter, the highest bext coefficient is 1540.53 ± 846.66 Mm-1, and the lowest in summer is 128.58 ± 58.00 Mm~(-1). The light extinction was mainly contributed by(NH_4)_2SO_4 and NH_4NO_3. There is a good correlation(R~2=0.81) between bext calculated by IMPROVE equation and bext-v obtained via Koschmieder formula. Multiple linear regression(MLR) method was further to reconstruct the empirical regression model of visibility as a function of PM_(2.5) aerosols chemical components, NO_2 and RH. In addition, Urumqi has a larger haziness(dv) coefficient. The results of source apportionment by Positive Matrix Factorization(PMF) model showed that secondary formation and industrial emission are the major source of light extinction.