Impacts of transboundary air pollution and local emissions on PM2.5 pollution in the Pearl River Delta region of China and the public health, and the policy implications

X Hou,C K Chan,S H L Yim,G H Dong

doi:10.1088/1748-9326/aaf493

Abstract

Despite a downward trend in pollutant levels because of a series of emission control policies, the Pearl River Delta (PRD) region continues to suffer from a high number of fine particulate matter (PM2.5) events and the resultant public health impacts. To effectively control PM2.5 in the region, a comprehensive understanding of source contribution and PM2.5 responses to various emission species is critical. We applied the Community Multiscale Air Quality Modeling System together with the high-order decoupled direct method, to simulate air quality and PM2.5 sensitivity and examined PM2.5 responses to emission species in the PRD region in the four seasons of 2010. We employed a concentration-response function to quantify the resultant number of premature mortalities attributable to outdoor PM2.5. We estimated that local and transboundary air pollution (TAP) contributed 27% and 73%, respectively, of the region’s PM2.5. In absolute terms, the largest impacts from local and TAP occurred in winter. With respect to relative contributions among the different sources, regional TAP (between cities in the region) (R-TAP) and local contributions had the largest effect in summer, whereas superregional TAP (from outside of the region) contributed the most in fall and winter. Outdoor PM2.5 pollution caused 20 160 (95% confidence interval: 5100–39 310) premature mortalities every year in the PRD region. Averaging among cities, 50%, 20%, and 30% of these deaths were attributable to S-TAP, R-TAP, and local contributions, respectively. Precursor gas emissions (i.e. NH3, volatile organic compounds, SO2, and NOx) affect PM2.5 level in a nonlinear manner; thus, individual pollutant control strategies are less effective for improving PM2.5 pollution than an integrated strategy. On the basis of our findings, we recommend that controls for multiple emission species should be implemented to control PM2.5 pollution in the region.

Highlights

Fine particulate matter (PM2.5; particles with an aerodynamic diameter 2.5 μm) pollution is a critical environmental problem in China, causing approximately 1.37 million premature deaths yearly (Gu and Yim 2016, Liu et al 2016, Gu et al 2018)
Previous studies have focused on PM2.5 source apportionment in the Pearl River Delta (PRD) region at the city level, but how the ambient PM2.5 level responds to changes in both primary and gaseous emissions of secondary PM should be investigated; detecting the major emission species and sources that contribute to the PM level is vital for formulating effective emission control measures
To provide valuable scientific references for policymakers for use in formulating effective emission control measures in the PRD region, we discuss the contribution of PM2.5 precursor gases to ambient PM2.5 and account for nonlinearity through assessing the PM2.5 sensitivity to individual emission species and cross-sensitivity between two emission species at various VOC/NOx ratios

Summary

Introduction

Fine particulate matter (PM2.5; particles with an aerodynamic diameter 2.5 μm) pollution is a critical environmental problem in China, causing approximately 1.37 million premature deaths yearly (Gu and Yim 2016, Liu et al 2016, Gu et al 2018). The Pearl River Delta (PRD) region is one of the fastest growing regions in China and has experienced serious air pollution issues (Yim et al 2010, Yang et al 2018, Wang et al 2019) because of its highly intensive energy consumption, which causes a high level of air pollution emissions. Scholars have reported transboundary air pollution (TAP) between the cities is a major contributor to the air pollution in the region (Louie et al 2005, Deng et al 2008, Gu and Yim 2016, Luo et al 2018, Tong et al 2018a, 2018b). Previous studies have focused on PM2.5 source apportionment in the PRD region at the city level, but how the ambient PM2.5 level responds to changes in both primary and gaseous emissions of secondary PM should be investigated; detecting the major emission species and sources that contribute to the PM level is vital for formulating effective emission control measures

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