Topographical differentiation characteristics of double high pollution of PM2.5 and ozone in the Beijing-Tianjin-Hebei region
摘要
In recent years, double-high pollution(DHP) events of fine particulate matter (PM2.5) and ozone (O₃) have become increasingly prevalent in China, with health impacts on populations significantly surpassing those of single pollutant exposures. This phenomenon exhibits considerable variability in regions characterized by complex topography, such as the Beijing-Tianjin-Hebei(BTH) region, thereby recognizing it as a critical zone for the prevention and control of DHP. This study analyzes the spatiotemporal distribution characteristics and influencing factors of the DHP in the BTH region, utilizing daily PM2.5 and O3 concentrations from the CHAP dataset spanning 2017 to 2022, while considering terrain differentiation and contrasting the pre- and post-COVID-19 epidemic periods as experimental environments. The findings indicate that: (1) The DHP in the four regions of BTH primarily occurred between April to July and in September. Compared to the pre-epidemic, the incidence of DHP days in the BTH region diminished by 68.18% following the epidemic. Moreover, the Taihang mountain and Yanshan low hill and hillock regions exhibited zero pollution during the summer subsequent to the epidemic. (2) In terms of spatial distribution, before the epidemic, the areas with high PM2.5 values (115–150 µg·m−3) were mainly located in the southern Inland plain and the southern Taihang mountain low hill and hillock region. The high O₃ area (190–205 µg·m−3) was concentrated in the northern Inland plain and the northern Taihang mountain low hill and hillock region and the southern Yanshan low hill and hillock region. Following the epidemic, PM2.5 concentrations generally decreased (75–85 µg·m−3), with the high-value area shifting to the Taihang mountain low hill and hillock region; the extent of O3 pollution was reduced, yet concentrations in the southern portion of the Yanshan low hill and hillock region increased significantly (215–265 µg·m−3), indicating a change in regional differentiation characteristics. (3) The DHP in the BTH region demonstrated a more concentrated low-low aggregation before and after the epidemic. Post-epidemic, the PM2.5 high aggregation shifted to more concentrated, whereas the opposite trend was observed for O3. (4) Prior to the epidemic, the centers of gravity for PM2.5 and O3 pollution were aggregated. Post-epidemic, the migration distance of these pollution centers increased markedly, with the Yanshan low hill and hillock region exhibiting a significant shift. The migration distances for the PM2.5 and O3 pollution centers reached 303.83 km and 303.45 km, respectively. Additionally, there was a trend for the pollution centers of gravity in each topographical subdivision to revert to their original aggregation by the epidemic’s conclusion. (5) The factor detector results indicated that the influence of DEM(Digital Terrain Model) on PM2.5 and O3 pollution increased significantly after the epidemic, with contributions of 83.85% and 80.65%, respectively. Moreover, the interaction detector results revealed that the interplay between topography and other variables intensified post-epidemic, hence enhancing the effects of the two pollutants. This establishes a scientific foundation for the investigation of DHP through topographic differentiation.