Distribution of fog and haze in Langfang and difference of wind field when coexisting with heavy polluted weather

By using National Centers for Environmental Prediction (NCEP) reanalysis data(1°×1°),wind profiler radar data, meteorological observation data, and environmental monitoring data, fog and haze distribution of Langfang from 2015 to 2018 were analyzed, and vertical wind field structure in fog and haze of air quality index (AQI) reaching heavy pollution was studied in depth. The results showed that the average annual number of haze days (47 d) in Langfang was more than that of fog days (31 d), and the spatial distribution was different to some extent. The monthly difference of haze was more significant than that of fog. Regional fog could occur all year round, reaching the peak in October, while haze was concentrated in autumn and winter, and the maximum number of haze days was in January. When AQI was greater than 200, the pollution level of fog was heavier than that of haze, with AQI daily average being 43 higher, the average surface wind speed 0.5 m/s lower, and the relative humidity about twenty-five percent higher. In fog, the surface wind was mainly calm or southeast wind, while in haze, it was mainly east-southeast wind. In the case of heavy pollution with fog, the low altitude was the west-southwest wind, while the heavy pollution with haze was mainly the northeast wind. In the case of fog or haze, there was a relatively small wind velocity layer in the lower space of 1 500 m (about 850 hPa).When the wind speed increased to 6-10 m/s below 3 000 m, it had a favorable effect on the diffusion of air pollutants. The greater the wind speed of the northwest wind, the lower the height, the more obvious the diffusion effect.