Characteristic and Spatiotemporal Variation of Air Pollution in Northern China Based on Correlation Analysis and Clustering Analysis of Five Air Pollutants

Air quality in Northern China has become a global hot spot issue due to a series of air pollution events in the recent years. In this study, five representative air pollutants (PM2.5, SO2, NO2, CO, and O-3) were employed to reveal the spatial and temporal distribution of air pollution in Northern China. Periodic decline in PM2.5, SO2, CO, and NO2 from 2016 to 2018 indicated that air pollution control measures have achieved desired results. In addition, PM2.5 was significantly positively correlated with SO2, CO, and NO2 (p < 0.001), and O-3 had negative correlations with the other four pollutants. Furthermore, the heavy pollution phenomenon in Shijiazhuang, Anyang, Xingtai, and Handan was attributed to their industrial structures (e.g., steel industry) and geographical location based on clustering analysis. Contrary to above four pollutants, the annual average concentrations of O-3 increased in all the nine cities (1.4-35.9%) from 2016 to 2018. It is necessary to plan mitigation strategy for O-3 based on further investigation of source and formation mechanism of O-3.