Impacts of snow cover on micrometeorological conditions and rural air quality in Northeast China

Snow cover is one of the most typical underlying surface types in Northeast China in winter. Snow cover can affect air quality potentially through changing atmospheric diffusion capacity, with the underlying physics awaiting a further exploration for Northeast China. Therefore, the impacts of snow cover on micrometeorological conditions and air quality were investigated using surface and tower meteorological observations from October 2019 to March 2020 in Fujin, a typical rural area in the Sanjiang Plain in Northeast China. Low atmospheric visibility and poor air quality were observed to occur more frequently on snow-cover days than on snow-free days, with visibility exhibiting a decreasing trend with increasing snow depth (< 8 cm). Compared with snow-free days, the presence of snow cover was found to produce weakened unstable stratification in the near-surface layer and lower daily surface sensible heat flux (reduced by 54.8%), mainly related to higher snow surface albedo (0.5–0.8), which can suppress the development of daytime atmospheric boundary layer height and vertical dispersion of air pollutants. Moreover, moister ambient conditions on snow-cover days presumably favored secondary aerosol formation and particle hygroscopic growth. Stronger wind speeds and shears, friction velocity, and turbulence kinetic energy were observed on snow-cover days than on snow-free days when the air was clean, probably due to smaller aerodynamic roughness length on snow cover. However, when air pollution occurred on snow cover, winds and mechanic turbulence decreased significantly, favoring aerosols' accumulation near the surface. These findings can facilitate a comprehensive understanding of the physical mechanism of air pollution occurring over a large portion of the snow-cover region in wintertime Northeast China and helpful for the pollution controls.