Characteristics of low visibility during the Spring Festival in the Su-Wan region and investigation of its multifactorial causes—Integrated analysis of air pollution and meteorological conditions based on multi-source data

During the Spring Festival, the concentrated setting off of fireworks and the large-scale population movement can cause short-term drastic fluctuations in regional air quality and visibility. This study, conducted in Jiangsu and Anhui, used hourly air quality monitoring data from 2023 to 2025 before and after the Spring Festival, along with ERA5 meteorological reanalysis data, and applied time series and correlation analysis to explore the spatiotemporal distribution and driving factors of air pollution and low visibility during the Spring Festival. The results showed that the PM₂.₅ concentration in the study area during the Spring Festival was generally higher than that before the festival, with an increase of 52% in 2024. The interannual differences were closely related to the intensity of firework control policies. Setting off fireworks on New Year's Eve could increase PM₂.₅ by 95% to 618% within hours (with significant interannual variations), making it the dominant factor contributing to the short-term pollution spike. However, the reduction in traffic emissions during the Spring Festival (NO₂ decreased by 20% to 34%) was not the main cause of the increase in PM₂.₅. Visibility was jointly regulated by PM₂.₅ and relative humidity. In a high-humidity environment (RH > 80%), medium concentrations of particulate matter could trigger low visibility events. These results can support differentiated firework control and joint air pollution prevention in Jiangsu and Anhui during the Spring Festival.