Transport Pathways and Potential Source Regions of PM2.5 on the West Coast of Bohai Bay during 2009–2018

Tianyi Hao,Qing Yao,Ziying Cai,Suqin Han,Shucheng Chen,Wenyan Fan

doi:10.3390/atmos10060345

Abstract

Mass concentration data for particulate matter with an aerodynamic diameter less than or equal to 2.50 μm (PM2.5) combined with backward trajectory cluster analysis, potential source contribution function (PSCF), and concentration weighted trajectory (CWT) methods were used to investigate the transport pathways and potential source regions of PM2.5 on the west coast of Bohai Bay from 2009 to 2018. Two pathways responsible for the transportation of high PM2.5 levels were identified, namely a southerly pathway and a northwesterly pathway. The southerly pathway represented the major transport pathway of PM2.5 for all seasons. As a regional transport pathway, it had the greatest impact in winter, followed by autumn. The southerly transport pathway passed over the Shandong and Hebei provinces before reaching Tianjin: Air masses were transported within the boundary layer (below 925 hPa), representing a slow-moving air flow. The northwesterly pathway mostly occurred in winter and autumn and passed over desert and semidesert regions in Outer Mongolia, the sand lands of Inner Mongolia, and Hebei. The air masses associated with the northwesterly pathway represented fast-moving airflows responsible for long-range transportation of PM2.5. Two potential source regions that contributed to high PM2.5 loadings on the west coast of Bohai Bay were identified, “southerly source regions” and “northwesterly source regions”. The southerly source regions, with weighted CWT (WCWT) values in winter greater than 140.00 μg/m3, were anthropogenic source regions, including southern Hebei, western Shandong, eastern Henan, northern Anhui, and northern Jiangsu. The northwesterly source regions, with WCWT values in winter of 80.00–140.00 μg/m3, were natural source regions, encompassing central Inner Mongolia and southern Mongolia. In addition, the southerly transport pathway passed though anthropogenic source regions, while the northwesterly transport pathway passed though natural source regions. The impacts of anthropogenic source regions on PM2.5 loadings on the west coast of Bohai Bay were greater than those of natural source regions.

Highlights

Due to rapid economic development and urbanization in the past few decades, there has been an escalating increase in energy consumption in China, with a corresponding deterioration of air quality [1]
The southerly transport pathway passed though anthropogenic source regions, while the northwesterly transport pathway passed though natural source regions
Seasonal and annual variations of PM2.5 concentrations from 2009 to 2018 in Tianjin are shown in National Air Quality Standards (75.00 μg/m3 ) [34] and exhibited considerable seasonal variations

Summary

Introduction

Due to rapid economic development and urbanization in the past few decades, there has been an escalating increase in energy consumption in China, with a corresponding deterioration of air quality [1]. Atmosphere 2019, 10, 345 atmospheric pollutants in China are complex mixtures of various sources [2]. One of the major air pollutants is particulate matter (PM), PM2.5 (with an aerodynamic diameter less than or equal to 2.50 μm), which remains a nationwide problem despite considerable abatement efforts. Beijing–Tianjin–Hebei is the most prominent area of air pollution in China [3]. PM2.5 is the major air pollutant in Beijing–Tianjin–Hebei [4]. The long-range transport of particulate matter adds to locally emitted PM2.5 , increasing the ambient concentrations of PM2.5 and exacerbating human health effects [5,6,7]. Effective PM2.5 control strategies require knowledge of transportation and source regions of PM2.5. It is important to determine transport pathways and potential source regions of PM2.5

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