内江市大气细颗粒物化学组成及其消光特征

Chemical characteristics of fine particle and its light extinction in Neijiang

2012—2013年在内江市环境监测站楼顶采集了PM_(10)和PM_(2.5)样品,并分析了颗粒物中金属无机元素、水溶性离子和碳质组分的质量浓度,以研究颗粒物的污染水平及其消光特性.采样期间,内江市的PM_(10)和PM_(2.5)浓度分别为(116.3±54.7)μg·m^(-3)和(78.6±36.8)μg·m^(-3);颗粒物污染冬季较重,其次为秋季,春季和夏季污染水平相当.内江市PM_(2.5)中以二次无机离子(SNA,42.5%)和有机物(OM,35.0%)污染最为突出,其次为地壳元素(Soil,11.4%)、元素碳(EC,5.2%)和微量元素(Trace,0.3%).高相对湿度和细颗粒物浓度是导致内江灰霾频发的主要原因,10km能见度对应的PM_(2.5)浓度界值为72.2μg·m^(-3).采用IMPROVE模型计算,内江市PM_(2.5)的平均散射系数为(504.6±293.2)Mm-1,吸光系数平均为(41.0±20.6)Mm-1;PM_(2.5)中硫酸盐对消光系数贡献最大,占40.0%;其次为有机物和硝酸盐,贡献率分别是29.2%和15.3%;EC的贡献率为7.3%.PM_(2.5)质量浓度与散射系数呈现出较强的线性关系(r=0.88),通过回归方程得到PM_(2.5)的质量散射效率为4.2 m^2·g^(-1).

PM samples were collected on the building roof of Neijiang Environmental Monitoring Centre in Sichuan Province of Southwest China during2012 to 2013. The mass concentrations of inorganic elements,water-soluble ions and carbonaceous aerosols were analyzed to study the chemical compositions of PM and its light extinction effect. During the sampling period,the annual average PM10 and PM2.5levels in Neijiang were（ 116.3±54.7）μg·m^-3and（ 78.6±36.8） μg·m^-3,respectively. PM loadings were highest in winter,medium in autumn and lowest in spring and summer. Secondary inorganic ions（ SNA） and organic matter（ OM） were the most abundant components in PM2.5,contributing 42.5% and 35.0% to the total mass,followed by soil elements（ 11.4%）,elemental carbon（ EC,5.2%）,and trace elements（ 0.3%）. Both high relative humidity and high levels of PM2.5were the key factors for the frequent haze occurrence in Neijiang,and the threshold PM2.5mass corresponding to atmospheric visibility lower than 10 km was 72.2μg m^-3. Calculated by the IMPROVE formula,the particulate scattering and absorption coefficient in Neijiang was（ 504.6 ± 293.2） Mm-1and（ 41.0 ±20.6） Mm^-1,respectively. Among the PM2.5chemical components,sulfate was the largest contributor to its light extinction（ 40.0%）,followed by OM（ 29.2%）,nitrate（ 15.3%） and EC（ 7.3%）. High correlation was found between PM2.5mass and scattering coefficient（ r = 0.88）,and the scatteringefficiency of PM2.5was 4.2 m^2·g^-1.