A study on haze dissipation factors and their thresholds over Beijing-Tianjin-Hebei area

Based on conventional observation data collected at weather stations over Beijing-Tianjin-Hebei area during 2006—2015 and daily reanalysis data of the NCEP/NCAR, several meteorological elements in stable atmosphere condition corresponding to haze formation and in transparent atmosphere condition corresponding to haze dissipation in the autumn and winter are statistically analyzed. The results show that precipitation in Beijing-Tianjin-Hebei area in the autumn and winter actually promotes the formation and maintenance of haze instead of washing it out. Haze dissipation over Beijing-Tianjin-Hebei area in the autumn and winter is mainly controlled by wind field factors. The atmospheric state for haze dissipation can be divided into three types. Under different atmospheric states, the contribution of each wind field factor to haze dissipation is different. The optimum threshold of wind field factor can be found by the "class difference maximum threshold segmentation method of iteration self-organizing data". According to the sensitivity of each wind field factors to haze dissipation and the correlation between the factors, the index factors of haze dissipation for the three types are found out. Using index iterative method, the atmospheric states in the autumn and winter of 2016 and 2017 are inspected. The results show that according to the haze dissipation index and its threshold value, the statically stable atmosphere and the transparent atmosphere can be well distinguished, which provides a good indication for the haze process. The interpretation and application of derf2.0 model products can provide technical support for objective prediction of haze process.