[Real-time Source Apportionment of PM2.5 and Potential Geographic Origins of Each Source During Winter in Wuhan]

Abstract

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 NH₄⁺, NO₃^-, and SO₄^2- 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.

Keywords: Wuhan; fine particles(PM2.5); real-time source apportionment; regional transportation; source regions.