Study of atmospheric visibility and its influence factors in six typical cities in China

The statistical methods such as linear correlation analysis and categorical variable analysis were employed to analyze the data of particulate matter and meteorological observations in six cities (Bayannaoer, Shijiazhuang, Langfang, Zhengzhou, Wuhan, Guangzhou) from 2019 to 2020. The influences of particulate matter concentration and atmospheric relative humidity on atmospheric visibility were investigated. The results indicated that there were significant differences in the annual variation of atmospheric visibility among the six cities, but the lowest values consistently occurred from December to February of the following year, and the annual variation pattern was generally consistent. The influences of meteorological conditions, relative humidity, and particulate matter concentration on visibility were apparent, with relative humidity indirectly affecting visibility through changes in the physicochemical properties of particulate matter, but with a relatively weak correlation. There was a good linear correlation between PM_2.5 concentration and visibility, mainly following a power function. Overall, relative humidity and particulate matter had a synergistic effect on visibility, and cities with higher relative humidity required stricter control of particulate matter. Additionally, the study found that when PM_2.5 concentration was higher than the threshold value, visibility did not continue to decrease with increasing particulate matter, but significantly improved only when PM_2.5 concentration was below the threshold value. There was a significant difference in PM_2.5 concentration between the turning point and the platform period point associated with visibility in each city.