南京城区夏秋季能见度与PM2.5化学成分的关系

为研究南京细颗粒物PM2.5化学成分与能见度的关系,于2011年8月4~17日和2011年10月31日~11月11日在南京城区采集PM2.5样品并分析其化学成分,同时对能见度、PM2.5、相对湿度等进行了同步观测.结果表明:南京城区夏季采样期间的能见度高于秋季,分别约为10.9km、7.5km,低能见度天PM2.5质量浓度较高,能见度与PM2.5的相关系数为-0.75.水溶性离子和总碳分别占PM2.5质量浓度的38%和26%,其中与能见度相关性较显著的是NO3-、SO42-、NH4+、EC.总消光系数的主要贡献者是颗粒物,达98.2%.8月首要消光组分是硫酸铵(NH4)2SO4,占47.0%,有机碳OC和硝酸铵NH4NO3分别占19.2%和14.3%;而11月是NH4NO3、(NH4)2SO4和OC,分别占29.3%、28.7%、26.8%.对不同相对湿度下的能见度和PM2.5化学成分进行拟合.进一步根据WRF/Chem细颗粒物化学成分模拟结果,分别利用拟合关系式和美国IMPROVE关系式,对2011年8月和11月能见度进行计算,与观测对比发现,利用本文拟合关系式计算的能见度结果优于IMPROVE关系式.

Relationship between atmospheric visibility and chemical composition of PM2.5 in the summer and autumn of Nanjing

To study the relationship between atmospheric visibility and chemical composition of PM2.5 in Nanjing, samples of PM2.5 were collected and chemical composition were analyzed from 4August to 17August and from 31 October to 11November 2011 in urban Nanjing, while observations of atmospheric visibility, PM2.5, relative humidity, etc. were conducted simultaneously. Investigations showed that atmospheric visibility in Nanjing was higher in summer (~10.9km) than that in autumn (~7.5km) during the sampling period. The correlation coefficient between atmospheric visibility and PM2.5 was -0.75which indicated the low visibility when the concentration of PM2.5 was high. Water-soluble ionic and carbonaceous components accounted for 38% and 26% of PM2.5concentration. The correlation between atmospheric visibility and NO3-、SO42-、NH4+、EC was significant. Particles, occupying 98.2%, was most important for ambient light extinction coefficient. The largest contributor to ambient light extinction in August was (NH4)2SO4(47.0%), OC and NH4NO3accounting for 19.2% and14.3%. (NH4)2SO4, NH4NO3 and OC contributed 28.7%、29.3% and 26.8% to light extinction coefficient in November. The atmospheric visibility were fit with chemical composition of PM2.5in different relative humidity ranges. Using the concentration of PM2.5 chemical composition simulated by WRF/Chem, the atmospheric visibility in August and November of 2011 was calculated with the fitting relationship formulae and the American IMPROVE formula, respectively. In general, the calculated visibility from the fitting relationship formulae was better than the IMPROVE formula comapred to observations.