武汉冬季大气 PM_(2.5)小时分辨率源贡献识别及潜在影响域分析

Real-time Source Apportionment of PM_(2.5)and Potential Geographic Origins of Each Source During Winter in Wuhan

冬季是我国大气细颗粒物(PM_(2.5))污染较为严重的时段,武汉市PM_(2.5)受到明显的区域传输影响.本研究基于小时分辨率PM_(2.5)组分观测数据,采用受体模型,解析武汉冬季大气PM_(2.5)各类源的实时贡献.结合轨迹聚类和浓度权重,识别影响各类源的传输路径和潜在源区.武汉冬季大气平均ρ(PM_(2.5))为(75.1±29.2)μg·m^(-3).观测期间共有两次污染过程,第一次污染过程主要受西北方向气团影响,水溶性离子升高是PM_(2.5)呈现高值的主要原因,ρ(NH^(+)_(4))、ρ(NO^(-)_(3))和ρ(SO^(2-)_(4))分别是清洁时段的1.6、1.7和2.1倍;第二次污染过程则以正东方向气团为主,二次有机组分有明显的生成.对武汉冬季大气PM_(2.5)贡献最大的是二次源(34.1%),其次是机动车尾气(23.7%)、燃煤(11.5%)、道路尘(10.9%)、钢铁冶炼(8.7%)和烟花爆竹燃放(5.7%),贡献最小的是生物质燃烧(5.3%).钢铁冶炼贡献量的日变化最高值出现在08:00[(17.5±18.8)μg·m^(-3)],最低值出现在01:00[(10.4±10.9)μg·m^(-3)],呈现白天贡献量高和夜晚贡献量低的现象;机动车尾气的贡献量在上午09:00[(42.1±24.8)μg·m^(-3)]和晚上20:00[(41.6±19.5)μg·m^(-3)]出现明显峰值.第一次污染过程中,二次源贡献率明显升高,表明西北来向气团的长距离传输有利于二次组分的生成和老化;第二次污染过程中,机动车尾气、燃煤、钢铁冶炼和道路尘的贡献率升高,其源区主要分布在本地、江西西北部和安徽南部的长江沿线,反映出沿江密集分布的工业过程、工业原料和产品运输导致的尾气排放和运输扰动产生的道路尘等对于武汉市冬季大气PM_(2.5)的影响.生物质燃烧的源区主要集中在河南、安徽、江苏、河北南部和山西西南部,冬季华北平原地区生物质燃烧排放的污染物经区域传输会对武汉产生影响.本研究可为识别武汉市冬季大气颗粒物来源和区域联防联控提供参考.

China has always suffered from serious atmospheric fine particle(PM_(2.5)) pollution in winter, and PM_(2.5)in Wuhan is particularly affected by regional transportation. Based on the hourly monitoring dataset of chemical components during the winter period, this study identified the real-time sources of PM_(2.5)in Wuhan using a positive matrix factorization(PMF) model. A cluster analysis of backward trajectories and the concentration weighted trajectory were applied to obtain the potential source regions and transportation routes. During the observation period, ρ(PM_(2.5)) was(75.1±29.2) μg·m^(-3), and there were two pollution episodes, one of which was mainly affected by the air masses coming from the northwest direction. In the first pollution episode, the increasing concentration of water-soluble ions was the main reason for the high PM_(2.5)value, and the concentrations of NH^(+)_(4), NO^(-)_(3), and SO^(2)-_(4) were 1.6, 1.7, and 2.1 times those during the cleaning period, respectively. The other episode was affected by the air masses coming from the east direction, and the secondary organic components were clearly formed. Secondary inorganic aerosol contributed the most(34.1%) to PM_(2.5), followed by vehicular exhaust(23.7%), coal combustion(11.5%), road dust(10.9%), iron-and steel-producing processes(8.7%), and firework displays(5.7%). Biomass burning contributed the least(5.3%). Our examination of the diurnal variation revealed that the maximum contribution of iron-and steel-producing processes appeared at 08:00 [(17.5±18.8)μg·m^(-3)], and the lowest was at 01:00 [(10.4±10.9)μg·m^(-3)], which stayed high in the daytime and low at night. The contribution of vehicular exhaust showed a double peak at 09:00 [(42.1±24.8)μg·m^(-3)] and 20:00 [(41.6±19.5)μg·m^(-3)]. In the first pollution period, the contribution rate of secondary inorganic aerosol increased significantly, indicating that the long-distance transport under the northwest air mass promoted the generation of secondary components. In the second pollution period, the contribution rates of vehicular exhaust, coal combustion, iron-and steel-producing processes, and road dust increased, mainly located in the local area, the northwest of Jiangxi and the south of Anhui province. This reflected the influence of industrial processes, road transportation, and dust contribution along the Yangtze River on PM_(2.5). Biomass burning had a relatively high contribution for air masses from the northern regions, including Henan, Anhui, the south of Hebei, and the southwest of Shanxi provinces. The regional transport of pollutants from biomass combustion in the North China Plain during the winter would have an impact on Wuhan. This study can provide scientific and technological support for identifying the causes of atmospheric haze pollution in Wuhan during the winter and for the joint prevention and control of atmospheric particulate matter.