Characteristics of atmospheric boundary layer and its relation with PM2.5 during winter in Shihezi, an Oasis city in Northwest China

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Based on low-level atmospheric meteorological elemental and pollutant data in the vertical direction observed during a tethered sonde sounding experiment from December 27, 2019 to January 14, 2020 this study analysed the atmospheric boundary layer vertical structure and its influence on winter PM2.5 concentrations in Shihezi City, Xinjiang, using Richardson number (Ri) profiling and correlation analysis to better understand the correlation between the atmospheric boundary layer structure and continuous heavy pollution in Shihezi City during winter. The results showed that heavy pollution continued during the observational period, and the diurnal variation in the atmospheric boundary layer disappeared. The atmospheric boundary layer structure tended to remain stable, and the average boundary layer height was only 109 m. The lengthy temperature inversion lifespan, high humidity, and low-wind layer near the surface primarily contributed to the sustained heavy pollution during winter in Shihezi City. Temperature and wind speed during heavy pollution events were negatively correlated with the PM2.5 concentrations in the near-surface layer. Stable atmospheric thermodynamic stratification with a cold lower layer and a warm upper layer in the atmospheric boundary layer weakens vertical atmospheric pollutant diffusion. Moreover, increased relative humidity (RH) is beneficial for hygroscopic aerosol particle growth and liquid-phase chemical reactions, thus worsening heavy pollution.