Multivariate data analysis of a severe air pollution event in Shihezi City, China

A severe air pollution event occurred from January 23 to February 12, 2024 in Shihezi City, China. To reveal the causes, pollutant sources, and the role of vertical atmospheric structure on the occurrence and development of this event and pollutant diffusion, the air pollution process and causal mechanisms were analyzed based on surface meteorological observation data, vertical observation data, and reanalysis data. The results showed that coarse particulate matter was mainly distributed in the range of 1000 - 1500 m in the upper atmosphere, and fine particulate matter was mainly distributed in 200 - 400 m, with the variation of low during the day and high at night. The analysis of 500 hPa circulation showed that this severe air pollution event was mainly caused by the stable stratification of the near-surface atmosphere and the small pressure gradient caused by the long-term control of high-pressure ridge that was not conducive to pollutant diffusion. The polluted air mass in the urban was difficult to diffuse due to temperature inversion and inhibition of boundary layer. The sand and dust transported from other regions were affected by the static wind to settle and mix, which aggravated the pollution degree of the urban air mass. The polluted air masses were transmitted between cities, while the long-distance transmission was not obvious.