Preliminary Analysis of the Upper Jet Role for Air Pollution in the Surface Layer in North China Plain in Winter

Studies have reported a certain relationship between severe near-surface air pollution in East Asia and the upper jet. This paper investigates the relationship between the East Asian jet along with related mechanisms and high-concentration air pollutants near the ground during winter through statistical analysis based on daily wind field, vertical velocity data, and ground pollutant from NCEP/NCAR, and meteorological element data from the Science Data Bank. The results indicate that the concentrations of particulate matter in the North China Plain were considerably higher in winter during 2013–2018. The average concentrations of PM_2.5 and PM₁₀ in the North China Plain were 80.65 μg m⁻³ and 118.62 μg m⁻³, respectively. The number of days exceeding environmental standards reached 459 d and 489 d for PM_2.5 and PM₁₀, respectively. The concentration of particulate matter showed a gradual downward trend over the years with an average PM_2.5/PM₁₀ ratio (about 0.65), which remained stable for several years. The concentration of air pollutants in the North China Plain has a significant relationship with the inverse phase variation of the intensity of the East Asian polar front and subtropical jets. This relationship may be influenced by the ground temperature and meridional wind. When the polar front jet is stronger in winter, the average intensity of the subtropical jet decreases, and the mass exchange between the two jets occurs through secondary circulation and is stabilized. North China Plain is present on the right side of the weakened subtropical jet, the updraft continues to weaken, the temperature rises, and enhanced anomalous southerly winds appear. These conditions are conducive to the accumulation of PM₁₀ in the central part of the North China Plain and PM_2.5 in the northern part of the North China Plain. When the polar front jet is weaker in winter, the strength of the subtropical jets in the mean state will be stronger, at which time the updraft is enhanced, the surface temperature is lowered, and there are weakened anomalous northerly winds appearing, which is unfavorable for PM₁₀ in the central part of the North China Plain, and PM_2.5 buildup in the northern part of the North China Plain at this time.