杭甬地区大气中含碳气溶胶特征及来源分析

Characteristics and Source Analysis of Atmospheric Carbonaceous Aerosols in the Cities of Hangzhou and Ningbo

为了研究杭甬地区大气气溶胶中含碳气溶胶的季节性变化和它们的来源,于2014年12月至2015年11月收集了杭州和宁波2个城市中4个采样点的PM_(2.5)样品,利用碳热光学分析仪测定了样品中8种碳组分,获得了有机碳(OC)和元素碳(EC)的质量浓度.在此基础上,估算了含碳气溶胶总量(TCA)和二次有机碳(SOC)的浓度水平,根据OC与EC的相关性、比值和不同碳组分的特征,分析了主要来源.结果表明:(1)杭甬地区总碳(TC)年均浓度为(14.3±4.1)μg·m^(-3),占年均PM_(2.5)浓度的(26.2±6.5)%;OC和EC的年均浓度分别为(11.3±3.4)μg·m^(-3)和(3.0±0.9)μg·m^(-3).4季中,冬季TC浓度最高;(2)杭甬地区估算的TCA年均浓度为(25.6±7.5)μg·m^(-3),占PM_(2.5)的(42.2±10.0)%,SOC占OC年均值的(41.1±5.5)%;(3)杭甬地区年均OC/EC比值为4.7±1.7,落在汽车尾气排放,煤炭燃烧和生物燃料燃烧的区间内,说明这些排放源都是含碳气溶胶的主要来源.各个采样点在秋冬季都具有更高的char-EC/soot-EC比值,表明了这2个季节生物质燃烧活动的贡献也不容忽视.

To investigate the seasonal variations and sources of carbonaceous aerosols in the cities of Hangzhou and Ningbo, field PM2.5 sampling was conducted at four representative sites （two urban, one suburban, and one rural） in this region from December 2014 to November 2015. A thermal/optical carbon analyzer was employed to analyze both organic carbon （OC） and elemental carbon （EC） contents in PM2.5 by identifying eight different carbon fractions, including OC1, OC2, OC3, OC4 ＋ OPC, EC1- OPC, EC2, and EC3. Based on these fractions, OC and EC were defined as OC1 ＋ OC2 ＋ OC3 ＋ OC4 ＋ OPC and EC1 ＋ EC2 ＋ EC3 - OPC, respectively; total carbon （TC） was calculated as the sum of OC and EC; and total carbonaceous aerosols （TCAs） were quantified via the sum of organic aerosols （ OAs; converted from OC） and EC. The results showed the following. （1）The annual average level of TC in this region was （14.3 ± 4. 1 ） μg·m-（-3）, accounting for （26.2 ± 6.5 ）% of the annual average PM2.5 concentration. The annual average OC and EC concentrations were （ 11.3 ± 3.4） μg·m-（-3） and （3.0 ± 0. 9 ）μg·m-（-3）, respectively. The highest TC level was observed in winter among the four seasons. （2）The annual average TCA concentration in this region was （25.6 ± 7.5 ）μg·m-（-3）, contributing （42.2 ± 10. 0）% of PMzs. In addition, secondary organic carbon （SOC） was also estimated by the commonly applied EC method. It was found that SOC contributed （41. 1 ± 5.5 ） % to OC on an annual average basis. （3） The sources of carbonaceous aerosols were determined using the correlation between OC and EC, OC/EC mass ratio, and different carbon fraction characteristics. The annual average OC/EC ratio in this region was 4.7 ± 1.7, which fails in the diagnostic ratio range for vehicular emissions, coal combustion, and biomass burning, indicating these sources are probably the major contributors of the regional carbonaceous aerosols. Moreover, a higher char-EC/soot-EC ratio was observed during winter and autumn at all sites, possibly implying the enhanced biomass burning activities during these two seasons.