2008～2018年武汉市BC气溶胶时间演变特征及其来源分析

黑碳(BC)作为最重要的吸收性气溶胶,其辐射强迫显著地改变大气边界层结构和近地面大气污染物的累积。基于2008～2018年武汉市BC和气象要素的观测数据,结合CWT潜在来源模型,分析了BC的时间演变特征和潜在来源分布。结果表明武汉BC平均质量浓度为6 926.4±4 090.6 ng/m³,Ångström指数(AAE)和液体燃料源对BC贡献占比(P)的平均值分别为0.98±0.44和76.6%,BC主要来自液体燃料的燃烧。2014～2017年BC质量浓度呈现显著的下降趋势,液体燃料对BC的贡献逐年增加。BC的季节分布为冬季(8 537.3 ng/m³)>春季(7 513.2 ng/m³)>秋季(6 820.2 ng/m³)>夏季(6 161.9 ng/m³),BC_liquid占比为秋季(80.0%)>冬季(77.3%)>春季(76.2%) >夏季(72.9%)。不同季节BC日变化特征不同。四个季节BC日变化在2008～2013年均以单峰型分布为主,而在2016～2017年则为双峰型分布。不同季节BC的潜在来源分布存在显著区别。潜在来源高值区在2008～2010年主要分布于武汉市的西南部,范围较小;而2016～2017年主要集中在武汉市周边地区,范围变大。潜在源区的演变反映了周边城市群对武汉市BC的影响逐渐变大,这可能是造成武汉市BC质量浓度日变化的年际差异的原因。

Characteristics of the Temporal Evolution and Source Apportionment of BC Aerosols in Wuhan from 2008 to 2018

As the most important light-absorbing aerosols in the atmosphere, the radioactive forcing of black carbon (BC) significantly influences the structure of the planetary boundary layer (PBL) and the accumulation of surface air pollutants. Based on the observation data of BC and meteorological elements in Wuhan from 2008 to 2018, combined with the CWT potential source model, the characteristics of temporal evolution and potential source apportionment of BC are analyzed. The results show that the average mass concentration of BC in Wuhan is 6 926.4±4 090.6 ng/m³, and the average values of the Ångström index (AAE) and the contribution of liquid fuel sources to BC (P) are 0.98±0.44 and 76.6%, respectively. BC is mainly derived from liquid fuels combustion. The mass concentration of BC showed a significant downward trend from 2014 to 2017, but the contribution of liquid fuels combustion to BC was increasing. The average mass concentration of BC is distributed as follows: winter (8 537.3 ng/m³)>spring (7 513.2 ng/m³)> autumn (6 820.2 ng/m³)>summer (6 161.9 ng/m³). The proportion of BC_liquid is autumn (80.0%)>winter (77.3%)> spring (76.2%)> summer (72.9%). The diurnal of BC are different in different seasons. The diurnal of BC is dominated by a unimodal distribution in the four seasons from 2008 to 2013, and is a bimodal distribution from 2016 to 2017. The characteristics of potential sources of BC in different seasons are significantly different. The high potential sources area were mainly distributed in the southwestern of Wuhan from 2008 to 2010, with a relatively small range region; while were mainly concentrated in the surrounding areas of Wuhan from 2016 to 2017, with a larger range region. The evolution of the potential source area reflects the increasing influence of the surrounding urban agglomeration on the BC of Wuhan, which may be the reason for the inter-annual difference in the diurnal variation of the BC mass concentration in Wuhan.