Distribution Characteristics of Six Criteria Air Pollutants Under Different Air Quality Levels in Cangzhou City, China

Abstract

The problem of urban air pollution has caused widespread concern and solving the problem of air pollution has become a primary research focus. Cangzhou is one of the "2+26" cities in the air pollution transmission channel in the Beijing-Tianjin-Hebei (BTH) region, and its regional advantage is obvious. To study the distribution characteristics of major air pollutants, the air quality index (AQI) and mass concentrations of six criteria air pollutants, including PM 2.5 , PM 10 , SO 2 , NO 2 , CO and O 3 , from 2014 to 2018 were used. Furthermore, by employing the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, the air pollutant concentration level, temporal variations and air mass trajectory characteristics under different air quality levels in Cangzhou city were analysed. The results showed that the mass concentrations of PM 2.5 , PM 10 , SO 2 , NO 2 and CO and PM 2.5 /PM 10 increased successively with increasing pollution level, while the mass concentration of O 3 was at a level of slight pollution, which first increased and then decreased. In the case of serious pollution, PM 2.5 and PM 10 were 3.3 and 2.4 times the Chinese Ambient Air Quality Standard (CAAQS) Grade II standard, respectively, and PM 2.5 /PM 10 was 0.71 times the standard, indicating that as pollution increased, the air pollution gradually became composed of mainly fine particles. The air quality was dominantly good and light, accounting for 73.4% to 84.7% of the total air quality from 2014 to 2018, respectively. The ambient air quality improved annually; the proportion of excellent and good days increased from 42.9% to 63.8%, and the proportion of severe and serious pollution days decreased from 12.2% to 3.7%. The diurnal variations in air pollutants were different under different air quality levels. The air mass trajectory analysis showed that as the pollution level increased, the proportion of eastern and easterly air masses decreased, and the proportion of western and westerly air masses increased gradually. Compared with the CAAQS Grade II standard, the excessive levels of particulate matter increased, and PM 2.5 was the most serious.