Episode study of fine particle and ozone during the CAPUM-YRD over Yangtze River Delta of China: characteristics and source attribution

Publication date: Available online 1 February 2019

Source: Atmospheric Environment

Author(s): Lei Shu, Tijian Wang, Min Xie, Mengmeng Li, Ming Zhao, Ming Zhang, Xiuyong Zhao

Abstract

Fine particle (PM_2.5) and ozone (O₃) are major air pollutants in China, especially in developed city clusters. A comprehensive field campaign, the Campaign on Air Pollution and Urban Meteorology in Yangtze River Delta (CAPUM-YRD), eastern China is carried out in 2016 to enhance the understanding of regional PM_2.5 and O₃ pollution. Two super sites in Shanghai, one in Hangzhou, as well as nineteen national monitoring stations in Nanjing and Hefei jointly participate in the campaign. In this study, regional PM_2.5 and O₃ pollution episodes are characterized based on summer and winter experiments during the CAPUM-YRD. Further, trajectory simulation and source apportionment technology in Comprehensive Air Quality Model with extensions (CAMx) are applied to reveal the source of the pollution episodes. We find regional synchronous PM_2.5 pollution episodes (over 120 μg/m³) occur frequently throughout YRD. Secondary inorganic and carbonaceous components account for a major proportion (70-80%) in PM_2.5. Nitrate concentration is significantly higher (lower) than sulfate in winter (summer). The secondary conversion of sulfur and nitrogen increases alongside elevated PM_2.5 levels, with a maximum ratio of 0.28 and 0.17 in winter, respectively. Source apportionment results suggest that the contribution of emissions within YRD dominates in PM_2.5 (over 60%) compared to other regions. The inter-regional transport from the north-northwest can contribute over 20% to PM_2.5 in YRD, with a maximum of 28.4% in Nanjing. Under the transport by enhanced northerly winds, PM_2.5 concentrations may increase explosively, with an observation evidence of peak values in Hefei (312.6 μg/m³) and Nanjing (255.7 μg/m³). Moreover, high levels and remarkable spatial heterogeneity of surface O₃ are observed over YRD in summer, with daily maximum 8-hour average O₃ above 300 μg/m³ in Nanjing. The occurrence of O₃ pollution episodes is significantly impacted by favorable stagnant weather conditions and transport at multiple spatial scales. Regional contribution results demonstrate that super-regional transport is prominent (29.4-50.7%) in O₃, especially in coastal cities like Shanghai (30.3-63.0%). Our results suggest that enhanced regional collaboration and efforts are of extreme necessity in long-term and optimized control of severe PM_2.5 and O₃ pollution in YRD.

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