Research On The Characteristics Of Atmospheric Environment Capacity In Hangzhou Under Different Weather Conditions In Winter

The formation of air pollution is closely related to meteorological conditions.When the emission of pollutants exceeds the natural purification capacity of the atmosphere,air pollution will form.Therefore,on the premise of a thorough understanding of meteorological conditions,objectively assessing the amount of pollutant emissions in the city,giving the atmospheric environmental capacity limit,and formulating a reasonable emission reduction policy are an important way to effectively reduce the occurrence of air pollution.Using the ground PM_2.5 mass concentration data,ERA5 reanalysis data and ground observation data in Hangzhou from 2015 to 2018,based on the objective classification of the winter weather situation in Hangzhou using the PCT classification method,its calculated by the revised A value method.The change characteristics of atmospheric environmental capacity under different weather conditions in winter in Hangzhou are shown.The results show that:（1）the air pollution concentration during the winter in Hangzhou continued to be high,and the air pollution was the most significant from 2015 to 2018.Through objective classification,it is concluded that the main weather conditions affecting Hangzhou in winter are divided into 6 types:high pressure control,high pressure bottom control equalizing field,L-type high pressure control,high pressure front control equalizing field,low pressure control,low pressure front Control the equalizing field.Among them,when high pressure control,high pressure bottom control equalizing field,L high pressure control,low pressure control,air pollution is easy to occur;while low pressure front control equalizing field and high pressure front equalizing field control,air pollution is not easy to occur.（3）The atmospheric environmental capacity of PM_2.5 under the six weather types are 1.88,1.10,3.70,7.25,-1.23,and 7.95 t/d;the atmospheric environmental capacity of PM₁₀ is 9.80,8.17,12.05,21.65,1.91 and 23.09 t/d;NO₂atmospheric environmental capacity is 6.53,7.75,8.17,11.85,2.39 and 12.92 t/d In addition,except for the negative value of PM_2.5 atmospheric environmental capacity in Hangzhou in winter under low pressure control,the other atmospheric environmental capacities of PM₁₀and NO₂ are all positive values,indicating that PM_2.5 is the most important pollutant that causes air pollution in Hangzhou.When Hangzhou is under low pressure control in winter,there is no room to emit PM_2.5.Only by reducing PM_2.5emissions can the occurrence of air pollution in Hangzhou be controlled.（3）Changes in meteorological conditions play an important role in the occurrence and extinction of air pollution,but the control of source emissions still plays a pivotal role.That is,the government’s emission reduction measures are particularly important.Through WRF-Chem simulation of 4 heavy pollution processes in Hangzhou under H,HB,HL and L type control,it is found that when anthropogenic emissions are reduced by 50%,60%,60%,and 70%respectively（that is,government emission reductions）To achieve the positive value of atmospheric environmental capacity,the mass concentration of PM_2.5 should be reduced to less than 75μg/m³,and the reduction of PM_2.5 needs to be reduced by 2.56,2.21,2.15 and 4.11t/d.