天津城区春季大气气溶胶消光特性研究

利用天津大气边界层观测站2011年4月1日~5月10日气溶胶散射系数、吸收系数、PM2.5质量浓度、大气能见度和常规气象观测数据,分析了气溶胶散射系数和吸收系数的变化特征,以及气溶胶消光系数与PM2.5质量浓度和大气能见度的关系,并对两种方法计算的消光系数进行了比较.结果表明,观测期间天津城区气溶胶散射系数为369.93 Mm-1,对大气消光贡献为86.7%,气溶胶吸收系数为36.32 Mm-1,对大气消光贡献为8.5%,单次散射反照率为0.91;气溶胶散射系数和吸收系数的日变化特征具有明显的双峰结构,对应于早晚交通高峰;不同天气类型下其日分布特征存在较大差异,霾日散射系数和吸收系数最高,沙尘日和降水日次之,晴日最低;气溶胶散射系数和吸收系数与PM2.5质量浓度呈线性正相关,与大气能见度呈指数负相关,观测期间气溶胶质量散射效率均值为2.95m2/g;采用Koschmieder’s公式反算能见度获得的大气消光系数,与通过测量气溶胶散射系数、气溶胶吸收系数、气体散射系数和气体吸收系数等分量加和获得的消光系数相比一致性较好,高相对湿度天气下能见度反算值高于各系数加和值.

Study on characteristic of aerosol extinction at Tianjin City in the spring

Based on the aerosol scattering and absorption coefficient,PM2.5 mass concentration,visibility and other observation data at Tianjin city,the characteristic of scattering and absorption coefficients and the relationship between aerosol extinction coefficient and PM2.5 mass concentration and visibility were analyzed.Two methods of calculating extinction coefficient were compared.The results indicated that mean aerosol scattering coefficient was 369.93Mm-1 and accounted for 86.7% of the extinction coefficient.Mean aerosol absorption coefficient was 36.32Mm-1 and accounted for 8.5%.The single scattering albedo was 0.91.Daily variation of aerosol scattering and absorption coefficients presented double-peak distributions corresponding to morning and evening rush hours.Aerosol scattering and absorption coefficients in haze days were highest and in dust days and rain days were middle and in sunny day were lowest.There was a good linear correlation between scattering or absorption coefficients and PM2.5 mass concentration and a typical negative exponential correlation with the visibility.The mean mass scattering efficiency was 2.95m2/g during observation period.The extinction coefficient retrieval from visibility with Koschmieder’s formula was consistent with the sum of observation aerosol scattering and absorption coefficients and gas scattering and absorption coefficients.The extinction coefficient retrieval value was higher than the observation when the relative humidity was higher than 80%.