万州城区空气污染过程中含碳气溶胶的变化特征

于2016年9月28日至10月15日在万州城区对气态污染物、颗粒物及其含碳气溶胶进行了在线连续观测,结合气象参数,分析了含碳气溶胶的污染特征。结果表明,此次持续污染过程主要由颗粒物污染造成,污染天PM₁₀和PM_2.5平均质量浓度分别为170.8、123.7μg/m^3,显著高于非污染天。污染天和非污染天PM_2.5、NO_x、有机碳(OC)及元素碳(EC)浓度的日变化都呈双峰,但污染天PM_2.5、NO_x和OC出现早峰值时间比非污染天推迟1～3h。污染天OC、EC的平均质量浓度分别为28.0、5.4μg/m^3,分别为非污染天的2.2、1.6倍。以非污染天的起始点作为参照点,得到污染天OC、EC的平均增长率分别为159.3%和73.0%,OC污染累积和二次转化贡献率分别为45.8%和54.2%,说明污染过程OC以二次转化为主。并用最小比值法估算了二次有机碳(SOC)含量,得到污染天和非污染天PM_2.5中SOC平均质量浓度分别为16.3、5.3μg/m^3,SOC在OC中的占比(以质量分数计)分别为56.1%和39.9%,污染天SOC占比增加,也证明污染过程OC以二次转化为主。污染天静风出现频率比非污染天高,在东南风的影响下,OC、EC易出现高浓度。

Characteristics of carbonaceous aerosols during air pollution episodes in the urban Wanzhou area

Continuous measurements of gas pollutants,particulates and carbonaceous aerosols contained were conducted to assess the characteristics of carbonaceous aerosols during a typical air pollution event in the urban Wanzhou from September 28th to October 15th,2016.The results showed that,this continuous pollution process was mainly caused by particulate pollution.The average concentrations of PM 10 and PM 2.5 during polluted days were 170.8 and 123.7μg/m^3,respectively,higher than those during non-polluted days.The diurnal variations of PM 2.5,NO x,organic carbon(OC)and elemental carbon(EC)showed significantly bimodal pattern in both polluted days and non-polluted days.However,the morning peak times of PM 2.5,NO x,and OC concentrations were delayed by about one to three hours during the polluted days.The average OC and EC concentrations were 28.0 and 5.4μg/m^3 during polluted days,which were 2.2 and 1.6 times of non-polluted days,respectively.Compared to the reference point(the first day of non-polluted day),the average growth rates of OC and EC were 159.3%and 73.0%during polluted days.It was estimated the secondary formation was more important than the accumulation process for the increase of OC during polluted days,which accounting for 54.2%and 45.8%,respectively.The secondary organic carbon(SOC)concentrations were estimated by the minimum OC/EC,and the concentrations of SOC during polluted days and non-polluted days were 16.3 and 5.3μg/m^3,accounting for 56.1%and 39.9%to OC,respectively,also verifying the secondary formation source.Higher static wind ratio appeared during polluted days and OC and EC concentrations were generally higher under southeastern conditions.