| Atmosphere Super Station of Chongqing was chosen to online observation meanwhile chemical experiments was conducted for appearing frequently of low visibility across the country and city of Chongqing in recent years in this paper. Change rule of atmospheric visibility and relationship between impact factors and atmospheric visibility were obtained.Chemical matting algorithm of PM2.5 in the summer of 2014 of Chongqing was establish by U.S. IMPROVE formula. Goodness of fit of extinction coefficient reconstructed by chemical matting algorithm and extinction coefficient value measured were verified. Then contribution of extinction coefficient(bexe) from impact factors in the summer of 2014 of Chongqing was acquired.According to visibility observational data for four years of Chongqing city, a four-year average visibility was 5430.15 m from 2011 to 2014, of which 2011 was 5268.28 m, 2012 was 4402.86 m, 2013 was 5960.79 m and 2014 was 6088.67 m. The lowest average visibility in nearly four years was 2012 and highest one was 2014. Difference of average visibility between 2012 and 2014 was 38%. Daily analysis of visibility in summer of 2014 showed that a higher atmospheric visibility appeared in summer, average value of visibility was 10580 m,value of visibility from 13:00 to 21:00 was higher than average value. Visibility declined steadily from 00:00, a lowest value of visibility was 8520 m, appeared at 08:00, then continue to grow, visibility was more than 10000 m after 12:00, a highest value of visibility was 13020 m, appeared at 17:00, then value of visibility started falling after this.The correlation of visibility and impact factors such as meteorological factor, PM10, PM2.5, NO2, NOx and other factors was analyzed by average daily sampled data collected in the summer of 2014.Relationship between impact factors and atmospheric visibility were obtained.The results showed that visibility had positive correlation with wind speed and air temperature, negative correlation with barometric pressure, relative humidity, PM10, PM2.5, NO2, NOx, of which relative humidity and PM2.5 are the main factors affecting visibility. Higher chemical composition concentration of air in summer were SO42-, EC, NH4+, which concentration were 12.461ug/m3, 5.83ug/m3 and 4.586ug/m3, respectively. Visibility had significant negative correlation with SO42-, NO3-, NH4+, Na+, K+, OC and EC, which correlation coefficient were 0.874,-0.547,-0.887,-0.585,-0.910,-0.858 and-0.826. Extinction effect of particulate matter were reinforced by character of absorption and scattering of substances above, so visibility declined.Air extinction coefficient in summer of 2014 of Chongqing was calculated by U.S. IMPROVE formula. A good linear of extinction coefficient between particulate matter reconstructed and value measured was obtained by comparing calculated value and measured one, correlation coefficient of line was 0.96, and its slope was 1.267, calculated value was lower than measured one, difference was 18%. The results indicated that chemical matting of Chongqing urban area was analyzed and calculated by IMPROVE formula corrected.Average air extinction coefficient was 258.39Mm-1 in summer of 2014 of Chongqing urban area, of which atmospheric aerosol scattering coefficient was 192.51Mm-1, 74% of the total extinction, its absorption coefficient was 43.28 Mm-1, 17% of total extinction, NO2 gas absorption coefficient and air-Rayleigh were 12.6Mm-1 and 10Mm-1, respectively. 9% of total extinction of two types of co-extinction, this indicated that significant factors that impacted air visibility was aerosol pollution, especially aerosol scattering. Atmospheric extinction coefficient contribution of sulfates, nitrates, OC, EC, CM, Soil, NO2 from PM2.5 were 35%, 4%, 24%, 20%, 10%, 2%, 5%, respectively. Among them, and the extinction coefficient contribution rate of sulfates, nitrates, OC and EC were more than 80%. So, the extinction coefficient contribution of PM2.5 chemical components, from most significant to least : sulfate > organic carbon > element carbon. |
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