Assessment of inter-city transport of particulate matter in the Beijing–Tianjin–Hebei region

Xing Chang,Siyi Cai,Shuxiao Wang,Bin Zhao,Jiming Hao

doi:10.5194/acp-18-4843-2018

Abstract

Abstract. The regional transport of particulate matter with diameter less than 2.5 µm (PM2.5) plays an important role in the air pollution of the Beijing–Tianjin–Hebei (BTH) region in China. However, previous studies on regional transport of PM2.5 mainly aim at province level, which is insufficient for the development of an optimal joint PM2.5 control strategy. In this study, we calculate PM2.5 inflows and outflows through the administrative boundaries of three major cities in the BTH region, i.e., Beijing, Tianjin and Shijiazhuang, using the WRF (Weather Research and Forecasting model)-CMAQ (Community Multiscale Air Quality) modeling system. The monthly average inflow fluxes indicate the major directions of PM2.5 transport. For Beijing, the PM2.5 inflow fluxes from Zhangjiakou (in the northwest) and Baoding (in the southwest) constitute 57 % of the total in winter, and Langfang (in the southeast) and Baoding constitute 73 % in summer. Based on the net PM2.5 fluxes and their vertical distributions, we find there are three major transport pathways in the BTH region: the northwest–southeast pathway in winter (at all levels below 1000 m), the northwest–southeast pathway in summer (at all levels below 1000 m), and the southwest–northeast pathway in both winter and in summer (mainly at 300–1000 m). In winter, even if surface wind speeds are low, the transport at above 300 m can still be strong. Among the three pathways, the southwest–northeast happens along with PM2.5 concentrations 30 and 55 % higher than the monthly average in winter and summer, respectively. Analysis of two heavy pollution episodes in January and July in Beijing show a much (8–16 times) stronger transport than the monthly average, emphasizing the joint air pollution control of the cities located on the transport pathways, especially during heavy pollution episodes.

Highlights

The Beijing–Tianjin–Hebei (BTH) region, one of the most developed regions in China, is suffering from severe pollution involving particulate matter with diameter less than 2.5 μm (PM2.5)
The positive total net fluxes in Beijing and Shijiazhuang reveal that the PM2.5 inflows of these two cities generally exceed the outflows, and that these cities act as a ”sink” of PM2.5
For Beijing, in winter, the inflow fluxes mainly come from Zhangjiakou and Baoding, and the outflows primarily go to Chengde and Langfang

Summary

Introduction

The Beijing–Tianjin–Hebei (BTH) region, one of the most developed regions in China, is suffering from severe pollution involving particulate matter with diameter less than 2.5 μm (PM2.5). According to the monitoring data from the China National Environmental Monitoring Center (http:// www.cnemc.cn/, last access: 10 January 2018), the average PM2.5 concentrations of the BTH region in 2013, 2014 and 2015 were 106, 93 and 77 μg m−3, respectively, which far exceeded the 35 μg m−3 standard in China. Reducing the PM2.5 concentration in the BTH region is critical. Emissions from one city can substantially affect the PM2.5 pollution in another city under particular meteorological conditions via the transport process. Some studies have shown that emissions from outside Beijing can contribute 28–70 % of the ambient PM2.5 concentration in Beijing A number of approaches have been applied to evaluate the inter-city transport

Methods

Results

Conclusion