成都碳质气溶胶变化特征及二次有机碳的估算

利用2020年6月~2021年5月在成都市观测的碳质气溶胶小时分辨率数据,分析了气溶胶中总碳(TC)、有机碳(OC)、元素碳(EC)和二次有机碳(SOC)的变化特征.结果表明:观测期间m(TC)、m(OC)、m(EC)和r(OC/EC)的年均值分别为(9.5±4.4)μg/m³,(6.4±3.2)μg/m³,(3.2±1.1)μg/m³,2.2±0.5.成都m(TC)、m (OC)、m (EC)均表现冬为季最高((15.8±8.2),(11.1±5.8),(4.6±2.5)μg/m³),春秋次之,夏季最低((6.1±0.9),(4.5±2.0),(2.7±1.4)μg/m³)的特征.r(OC/EC)季节均值(1.9~2.6)以及四个季节的m(TC)、m(OC)、m(EC)呈现早(07:00~09:00)晚(22:00~01:00)“双峰”的日变化特征,表明机动车排放源对成都碳质气溶胶的影响较大.春夏季OC与EC的相关性小于秋冬季,表明春夏季OC、EC来源差异较大.由EC示踪法和最小相关性法得到m(SOC),r(SOC/OC)在夏季最大(40.4%),冬季最小(27.3%).春、夏季SOC与O₃呈显著正相关,表明较强的光化学反应对SOC生成有重要贡献.选取各季节连续高m(TC)时段与季节平均作对比,发现碳质气溶胶有明显夜间积累过程,夏季高浓度时段二次生成使得m(OC)增长显著高于m(EC),r(OC/EC)也迅速上升.

Characteristics of carbonaceous aerosols and estimation of secondary organic carbon in Chengdu

To investigate the diurnal and seasonal characteristics of carbonaceous aerosols in Chengdu, mass concentrations of total carbon (TC), organic carbon (OC), elemental carbon (EC), and secondary organic carbon (SOC) were continuous hourly measured from June 2020 to May 2021. The results showed that the annual mean values of m(TC), m(OC) and m(EC) during the observation periods were (9.5±4.4) μg/m³, (6.4±3.2) μg/m³ and (3.2±1.1) μg/m³, respectively, with the ratio of r(OC/EC) at 2.2±0.5. The m(TC), m(OC) and m(EC)in Chengdu peaked in winter ((15.8±8.2), (11.1±5.8), (4.6±2.5) μg/m³), followed by spring and autumn, and reached to the lowest level in summer ((6.1±0.9), (4.5±2.0), (2.7±1.4) μg/m³).The seasonal means of r(OC/EC) were in the range of 1.9~2.6, and the diurnal variations in m(TC), m(OC) and m(EC) followed the "bimodal" pattern which peaked in the morning (07:00~09:00) and the evening (22:00~01:00).This indicated significant contributions of motor vehicle emissions on carbonaceous aerosols in Chengdu. The correlation between OC and EC wasweaker in spring and summer than in autumn and winter, indicating that the sources of OC and EC were quite different in spring and summer. The m(SOC), which was estimated by the EC-tracer method and the Minimum R-Squared method, and the r(SOC/OC) was the largest in summer (40.4%) and the smallest in winter (27.3%). The significant positive correlation between SOC and O₃ in spring and summer revealed that photochemical reactions contributed significantly to the formation of SOC. The continuous high m(TC) periods in each season were selected for comparison with the seasonal averages. The results showed that carbonaceous aerosols had obvious nocturnal accumulation process. The m(OC) increased significantly higher than that of m(EC) due to the secondary production during the high concentration periods in summer, and the r(OC/EC) also increased rapidly during these times.