基于MERRA-2再分析资料的上海市近40年大气黑碳浓度变化及潜在来源解析

Changes and Potential Sources of Atmospheric Black Carbon Concentration in Shanghai over the Past 40 Years Based on MERRA-2 Reanalysis Data

黑碳(black carbon,BC)作为大气气溶胶的重要组成部分,因其粒径小、比表面积大和辐射强迫等,对区域和全球辐射平衡、气候和人体健康产生巨大影响.以高度城市化的上海市为研究区域,基于MERRA-2再分析数据资料和地面观测数据,利用M-K趋势检验、后向轨迹和潜在源贡献函数(potential source contribution function,PSCF)探究了上海市1980~2019年大气BC浓度的时空变化特征及局地排放和区域传输的影响.结果表明:(1)MERRA-2大气BC浓度和地面观测数据具有较好的趋势一致性(R∈[0.68,0.72]),表明MERRA-2再分析资料可以用来有效揭示地面大气BC浓度的长期变化.(2)上海近40年大气BC浓度可分为3个阶段:缓慢增长的"低值"阶段[1980~1986年,(1.75±0.17)μg·m^(-3)],相对稳定的"中值"阶段[1987~1999年,(2.18±0.07)μg·m^(-3)]和波动变化的"高值"阶段[2000~2019年,(3.07±0.31)μg·m^(-3)];就季节变化而言,上海BC浓度总体呈夏季浓度低,冬季浓度高的"U"型模式;受水运货运船舶柴油机等发动机黑碳排放的影响,7月出现BC浓度小高峰.(3)大气污染物诊断质量比及双变量相关分析[R(BC-NO_(2))>R(BC-CO)>R(BC-SO_(2))]表明,交通排放是上海大气BC的主要排放源,尤其是重型柴油车的影响.(4)后向轨迹和PSCF分析发现上海夏季气团以清洁海风为主导,占77.18%;其他季节来自北方的气团超过50%.上海大气BC潜在源区主要分布在中国东部地区,以长三角为中心向外扩张,且扩张方向与后向轨迹方向一致.

As an important component of atmospheric aerosols,black carbon(BC)has a great influence on the regional and global radiation balance,climate,and human health due to its small particle size,large specific surface area,and radiative forcing potential.Here,the spatio-temporal characteristics of atmospheric BC were investigated based on modern-era retrospective analysis for research and applications version 2(MERRA-2)reanalysis data and ground observation data during 1980-2019 in Shanghai,a highly urbanized city in China's Mainland.The influences of local emissions and regional transmission on regional-scale BC concentrations were examined using the M-K trend test,backward trajectory analysis,and the potential source contribution function(PSCF).The results showed that:(1)MERRA-2 BC and ground observation datasets showed good consistency(R∈[0.68,0.72]),indicating that MERRA-2 reanalysis data can be used to reveal long-term changes in ground-level atmospheric BC concentrations;(2)Atmospheric BC concentrations in Shanghai over the past 40 years can be divided into three stages:a"low value"stage of slow growth[1980-1986,(1.75±0.17)μg·m^(-3)],a relatively stable"median value"stage[1987-1999,(2.18±0.07)μg·m^(-3)],and a fluctuating"high value"stage[2000-2019,(3.07±0.31)μg·m^(-3)].Seasonally,Shanghai’s BC concentrations generally show a"U"pattern with low concentrations in summer and high concentrations in winter.As a result of black carbon emissions from marine diesel engines and other engines used for water transportation,a small peak also occurs in July;(3)The diagnostic quality ratio of air pollutants and the bivariate correlation analysis[R(BC-NO_(2))>R(BC-CO)>R(BC-SO_(2))]indicated that traffic emissions were the main sources of atmospheric BC in Shanghai,especially by heavy diesel vehicles;(4)The backward trajectory and PSCF analyses found that the air mass of Shanghai in summer was dominated by a clean sea breeze,accounting for 77.18%.In contrast,during the other seasons,more than 50%of the air mass came from the north.The potential source regions of atmospheric BC in Shanghai are mainly distributed in eastern China,expanding outwards and centering on the Yangtze River Delta,and the expansion direction is consistent with the directions of the backward trajectories.