*Article* **Analysis of the Interactions between the 200 hPa Jet and Air Pollutants in the Near-Surface Layer over East Asia in Summer**

**Wen Wei 1, Bingliang Zhuang 1,\*, Huijuan Lin 1, Yu Shu 2,\*, Tijian Wang 1, Huimin Chen <sup>1</sup> and Yiman Gao <sup>1</sup>**

<sup>1</sup> School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China; mg1928050@smail.nju.edu.cn (W.W.); mg1928012@smail.nju.edu.cn (H.L.); tjwang@nju.edu.cn (T.W.); mg1728037@smail.nju.edu.cn (H.C.); mg20280011@smail.nju.edu.cn (Y.G.)

<sup>2</sup> Nanjing Meteorological Bureau, Nanjing 210019, China

**\*** Correspondence: blzhuang@nju.edu.cn (B.Z.); njushuyu@sina.com (Y.S.)

**Abstract:** The rapid economic development in East Asia has led to serious air pollution problems in the near-surface layer. Studies have shown that there is an interaction between air pollution and the East Asian upper-level jet, which is an important weather system controlling the climate in East Asia. Therefore, it is of great significance to study the relationship between the surface layer air pollutants and the upper-level jet stream in East Asia. Based on the daily wind and vertical velocity data provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research as well as the surface pollutant and meteorological variable data provided by the Science Data Bank, we use statistical analysis methods to study the relationship between the East Asian upper-level jet and the high-concentration area of near-surface air pollutants in summer. Meanwhile, the mechanisms of the interaction are preliminarily discussed. The results show that the North China Plain and the Tarim Basin are the high-value areas of the particulate matter (PM) in summer during 2013–2018, and the ozone (O3) concentration in the near-surface atmospheric layer in the North China Plain is also high. The average concentrations of the PM2.5, PM10 and O3 in the North China Plain are 45.09, 70.28 and 131.27 μg·m<sup>−</sup>3, respectively, and the days with the concentration exceeding the standard reach 401, 461 and 488, respectively. During this period, there is an increasing trend in the O3 concentration and a decreasing trend in the PM concentration. The average ratio of the PM2.5 to PM10 is approximately 0.65 with a decreasing trend. The air pollutant concentration in this region has a significant relationship with the location of the East Asian upper-level jet. The low wind speed at the surface level under the control of the upper-level jet is the main reason for the high pollutant concentration besides the pollutant emission. They relate to each other through the surface humidity and the meridional and zonal wind. Meanwhile, the concentrations of the PM2.5 and PM10 are high in the near-surface layer in the Tarim Basin, and the average concentrations are 45.19 and 49.08 μg·m<sup>−</sup>3, respectively. The days with the concentration exceeding the standard are 265 and 193, respectively. The interannual variation in the PM concentration shows an increasing trend first and then a decreasing trend. The average ratio of PM2.5 to PM10 in this region reaches approximately 0.9. The ratio reaches the highest in 2013 and 2014 and then decreases to and maintains at approximately 0.85. The concentration of air pollutants in the basin has a significant relationship with the intensity of the upper-level jet in East Asia. The weakening of the upper-level jet will lead to a decrease in the surface humidity in the northern part of the basin, an increase in the surface temperature in the western part of the basin and a decrease in the surface zonal wind in the eastern part of the basin, which will result in a higher PM concentration.

**Keywords:** East Asian upper-level jet; atmospheric particulate matter; ozone; surface meteorological variables; statistical analysis
