减排背景下成都大气PM_(2.5)碳质组分特征

Characteristics of Carbonaceous Species in PM_(2.5) in Chengdu Under the Background of Emission Reduction

近年来,国务院颁布的《大气污染防治行动计划》和《打赢蓝天保卫战三年行动计划》对我国空气质量的全面改善起到了重要作用,然而,当前鲜有对四川盆地两大政策实施效果进行评估以及对政策实施后PM_(2.5)化学组分新特征的针对性研究.2017年和2020年分别是两大污染减排政策实施效果评估的关键时期,为对两时期成都市大气PM_(2.5)及其中碳质组分特征进行全面了解,分别于2016年10月至2017年7月和2020年12月在成都市区进行了PM_(2.5)的连续采样,并对其中有机碳(OC)和元素碳(EC)进行了分析.结果表明:①2016~2017年成都市ρ(PM_(2.5))平均值为(114.0±76.4)μg·m^(-3),最高值出现在冬季,可达(193.3±98.5)μg·m^(-3),是浓度最低季节春季[(73.8±32.3)μg·m^(-3)]的2.6倍,而这种严重的冬季污染在2020年出现了明显改善,对应的ρ(PM_(2.5))为(96.0±39.3)μg·m^(-3),降幅达50.3%.②2016~2017年ρ(OC)和ρ(EC)的平均值分别为(21.1±16.4)μg·m^(-3)和(1.9±1.3)μg·m^(-3),分别占PM_(2.5)的质量分数为18.5%和1.7%;ρ(OC)季节变化特征为:冬季[(40.6±21.5)μg·m^(-3)]>秋季[(17.0±7.0)μg·m^(-3)]>夏季[(14.4±3.9)μg·m^(-3)]>春季[(12.6±6.0)μg·m^(-3)],而各季节ρ(EC)水平接近(1.3~2.4μg·m^(-3));二次有机碳(SOC)是OC的重要组成,可占OC的质量分数为44.5%.相比2016年冬季,2020年冬季ρ(OC)降至(19.2±9.1)μg·m^(-3),降幅达52.7%,EC则升高了26.1%.③随污染加重,各碳质组分及其贡献变化趋势各异,相比2016年冬季,2020年冬季OC随污染加重贡献更加趋于稳定,而SOC占比升高更为明显,二次有机组分贡献不容忽视.④各季节气团来向和污染物潜在源区均呈现出了明显差异;与2016年冬季相比,虽然2020年冬季主要气团来向未发生明显变化,但各轨迹对应的污染物浓度均出现了大幅降低,且污染物潜在源区向东部区域扩展明显.

The Air Pollution Prevention and Control Action Plan and Three-year Plan on Defending the Blue Sky promulgated by the State Council of the People’s Republic of China have played an important role in the overall improvement of air quality in China.However,few studies have evaluated the implementation effects of these two policies in Sichuan Basin and the new characteristics of PM_(2.5)chemical components after the implementation of these policies.The key periods for evaluating the implementation effects of these two pollution reduction policies are 2017 and 2020,respectively.In order to study the atmospheric PM_(2.5)and carbonaceous species in Chengdu during these two periods,this study sampled the PM_(2.5)in Chengdu from October 2016 to July 2017 and December 2020,respectively,and the organic carbon(OC)and elemental carbon(EC)were analyzed.The results showed that the annualρ(PM_(2.5))from 2016-2017 in Chengdu was(114.0±76.4)μg·m^(-3).The maximum value of theρ(PM_(2.5))appeared in winter[(193.3±98.5)μg·m^(-3)],and the minimum value appeared in spring[(73.8±32.3)μg·m^(-3)].By contrast,theρ(PM_(2.5))in winter decreased significantly in 2020,with a value of(96.0±39.3)μg·m^(-3).The annualρ(OC)andρ(EC)from 2016-2017 were(21.1±16.4)μg·m^(-3)and(1.9±1.3)μg·m^(-3),which accounted for 18.5%and 1.7%of the PM_(2.5)mass,respectively.The seasonal variation characteristic ofρ(OC)was:winter[(40.6±21.5)μg·m^(-3)]>autumn[(17.0±7.0)μg·m^(-3)]>summer[(14.4±3.9)μg·m^(-3)]>spring[(12.6±6.0)μg·m^(-3)],whereas theρ(EC)in the four seasons were close,ranging from 1.3 to 2.4μg·m^(-3).The annualρ(SOC)was(9.4±9.1)μg·m^(-3),which accounted for 44.5%of the OC mass.Compared with that in winter 2016,theρ(OC)decreased by 52.7%in winter 2020,whereas theρ(EC)increased by 26.1%.With the aggravation of pollution,the change trends of carbon species and their contributions were different.Compared with that in winter 2016,the variation in the contribution of OC with the aggravation of pollution in winter 2020 was more stable,whereas the proportion of SOC increased more obviously.There were obvious differences in the direction of air masses and the potential source area of pollutants in each season.Although there was no significant change in the direction of air masses in winter 2020 compared with those in winter 2016,the pollutant concentrations corresponding to each cluster decreased significantly,and the potential source area of pollutants expanded significantly to the eastern area.