杭州黑碳气溶胶污染特性及来源研究

2011年7月~2012年6月对黑碳气溶胶(BC)、PM2.5、污染气体及气象因子进行同步观测,以评估杭州市BC污染特征、来源分布及对大气能见度的影响.结果表明:杭州市大气BC日均浓度范围为1.3~16.5μg/m3,年均值达到(5.1±2.5)μg/m3.BC呈明显的季节变化趋势,秋冬季高,夏季低.BC也呈典型的日变化趋势,交通高峰期高,下午低,同时与NOx呈较好的相关性,表明城市中BC受到机动车尾气排放的重要影响;而BC/CO低于其他城市则表明生物质燃烧排放可能是杭州BC的另一大重要来源.BC随风速下降呈上升趋势, BC超过10μg/m3的高浓度事件中,风速基本低于2m/s,北-西北-西风对高浓度BC的输送作用明显.观测期间BC的吸收系数为(44.8±23.0)Mm-1,占到总消光比例的10.4%.灰霾和重度灰霾天气下,吸收系数分别为(66.2±30.1),(100.2±49.2)Mm-1,达到非霾天气的2.2和3.4倍, 表明BC吸收消光作用是影响杭州市大气能见度下降和灰霾天气发生的重要因素之一.

Characteristics and source of black carbon aerosol pollution in Hangzhou

In order to study the characteristics and source of black carbon pollution and its influence on visibility in Hangzhou, concentrations of black carbon, PM2.5, gaseous pollutants as well as meteorological factors were simultaneously monitored from July 2011 to June 2012. The annual mean BC concentration in Hangzhou was found to be (5.1±2.5)μg/m3, with a range of 1.3to 16.5μg/m3. BC concentrations showed strong seasonality, high in winter and autumn and low in summer. The BC concentrations also varied diurnally, with high values at rush hours and low values in the afternoon, showing strong correlations with NOx, which indicated the significant influence of vehicle emission on BC in urban area. The regression slope of BC/CO was found lower in Hangzhou than those in other sites, suggesting that biomass burning emission could be another important source of BC in Hangzhou. BC concentration increased as wind speed decreased. The wind speed was generally lower than 2m/s when BC concentration exceeded 10μg/m3. North, northwest and west wind had obvious transportation effect on high BC concentration in Hangzhou. The absorption coefficient of BC was (44.8±23.0)Mm-1 during the observation, accounting for 10.4 percent of the total light extinction. The absorption coefficients were (66.2±30.1) and (100.2±49.2)Mm-1in hazy and heavy hazy weather, respectively, which were 2.2 and 3.4times as large as in non-hazy weather, indicating that BC absorption light extinction was one of the main factors for visibility degradation and hazy weather in Hangzhou.