Source Contributions to PM2.5 under Unfavorable Weather Conditions in Guangzhou City, China

摘要

Historical haze episodes (2013-16) in Guangzhou were examined and classified according to synoptic weather systems.Four types of weather systems were found to be unfavorable,among which "foreside of a cold front" (FC) and "sea high pressure" (SP) were the most frequent (＞ 75％ of the total).Targeted case studies were conducted based on an FC-affected event and an SP-affected event with the aim of understanding the characteristics of the contributions of source regions to fine particulate matter (PM2.5) in Guangzhou.Four kinds of contributions-namely,emissions outside Guangdong Province (super-region),emissions from the Pearl River Delta region (PRD region),emissions from Guangzhou-Foshan-Shenzhen (GFS region),and emissions from Guangzhou (local)-were investigated using the Weather Research and Forecasting-Community Multiscale Air Quality model.The results showed that the source region contribution differed with different weather systems.SP was a stagnant weather condition,and the source region contribution ratio showed that the local region was a major contributor (37％),while the PRD region,GFS region and the super-region only contributed 8％,2.8％ and 7％,respectively,to PM2.5 concentrations.By contrast,FC favored regional transport.The super-region became noticeable,contributing 34.8％,while the local region decreased to 12％.A simple method was proposed to quantify the relative impact of meteorology and emissions.Meteorology had a 35％ impact,compared with an impact of-18％ for emissions,when comparing the FC-affected event with that of the SP.The results from this study can provide guidance to policymakers for the implementation of effective control strategies.