Study On The Characteristics Of Haze And The Controlling Meteorological Factors In Four Polluted Regions Of China

In the past decades,frequent haze events in the central and eastern China had a serious detrimental impact on the health of residents and severely impaired the visibility,particularly in the winter season when atmospheric conditions conducive to the accumulation of haze prevailed.Effective reduction of haze through emission control has been a top priority of the government which tries to balance the environmental protection and economic development.The concentration of haze is mainly determined by its emission sources and atmospheric transport?climate/meteorology?.In this study,we analyze the spatial and temporal distributions of haze in the four major pollution areas of China,namely Beijing-Tianjin-Hebei,Yangtze River Delta,Pearl River Delta and Sichuan Basin.The key meteorological factors affecting haze in different regions were identified by composite analysis and bootstrap method.The effect of climate/meteorology factors and emission on PM_2.5 concentration were quantitatively investigated by using“Optimum one-stepwise linear regression”.Correlation analysis and detrend analysis are used to identify the major climate factors that have significant effects on the winter haze concentrations in all four regions.Finally,the correlation analysis method,optimal total subset regression method and multiple linear regression method were used to develop an empirical prediction model for the haze days in the four regions for the winter months December,January and February.In the Beijing-Tianjin-Hebei region,there was no obvious trend of haze days for 40 years from 1973 to 2012.But there was a drastic growth after 2012,which was characterized by high relative humidity and temperature,weakened northerly wind and increased vertical stability.Similar meteorological factors affect haze days in the Yangtze River Delta,but this region has maintained a steady growth and is in the historical high values in recent years.Haze days in the Pearl River Delta gradually increased from 1973 to 2006,and then declined,mainly due to the weakening of the westerly and northerly winds,as well as the influence of the warm and wet air flow from the ocean.Haze days in Sichuan Basin have no obvious trend,and the generation of haze in this region is affected by the abnormal warming and increase of vertical stability.Using a stepwise linear regression method,the contribution of meteorology/climate to PM_2.5concentrations in the four regions is found to have a lower limit of 23%,17%,10%and 20%respectively.Global warming and the Pacific Decadal Oscillation are found to be the major climate factors affecting the haze concentrations in the four regions.These climate factors can be used as a basis for developing empirical models that are capable of monthly-to-seasonal forecast of winter haze days in the four regions.Some preliminary promising results are presented in this study.However,major uncertainties and challenges remain in these models which can only be successfully addressed in future studies that can identify and understand all critical climate factors affecting the winter haze days in the four regions.