Study On The Classification Of Polluted Weather During The Heating Period In Lanzhou

With the continuous development of China's economy,the acceleration of urbanization and industrialization,and the substantial increase in car ownership,the emissions of atmospheric pollutants have also increased significantly.The air pollution problem in many cities has become increasingly serious,and the pollution characteristics have gradually changed from a single soot type.Pollution has transformed into compound pollution,and the scope of pollution has also expanded from local pollution to regional pollution.Air pollution will not only cause an increase in the incidence of diseases such as the respiratory system and cardiovascular and cerebrovascular diseases,and endanger human health.It will also adversely affect the ecosystem,production and life,and weather.Therefore,urban air pollution has become a focus of public attention.Air quality is affected by topography,pollution source emissions,and meteorological conditions as a combination of factors.Meteorological conditions such as wind speed and atmospheric temperature stratification determine the diffusion,transmission,wet and dry deposition,and chemical transformation of pollutants,and the weather situation produces local weather conditions Important impact,therefore,studying the pollution characteristics under different weather types is of great significance for identifying the type of polluted weather,providing the accuracy of pollution prediction,and then alerting heavily polluted weather.In this paper,based on the time-lapse concentration data of air pollutants in Lanzhou City from 2012 to 2016,statistical analysis was made on the time-varying characteristics of the six standard pollutant concentrations in Lanzhou City and the AQI.The PCT objective weather classification method was used to classify the850hPa and 700hPa geopotential heights and temperatures at 08:00 daily for the four consecutive years of heating during 2012-2016.The 31 clusters corresponding to the maximum clustered interpretation variance?ECV?were selected According to the change characteristics of pollutant concentration and air quality index AQI,nine types of polluted weather and four types of clean weather were identified,and the differences of circulation characteristics and meteorological parameters under different weather types were further analyzed.Finally,the rationality of weather classification was tested through the two polluted weather processes in Lanzhou in winter.The main conclusions of the paper are as follows:?1?According to the interannual and monthly changes of the air quality index AQI,the polluted weather in Lanzhou is mainly concentrated in the heating period;NO₂,PM₁₀0 and PM_2.5.5 are the main pollutants in the Lanzhou area that have exceeded the standard in recent years.During the heating period,the most polluted weather with PM₁₀0 and PM_2.5.5 as the main pollutants.?2?In this paper,the PCT objective weather classification method is used to study the altitude and temperature of Lanzhou heating period.The clustering interpretation variance?ECV?is used to evaluate the results of each classification.According to the variation characteristics of particulate matter concentration and AQI index,nine polluted weather types and four clean weather types can be selected,accounting for43.8%of the total number of samples.?3?The particle concentration and AQI index values of the nine polluted weather types and the four clean weather types are quite different,indicating that the weather classification results selected in this paper contain significant differences in the number of polluted weather,particulate concentration,and ambient air quality levels.?4?By analyzing the circulation situation and wind field distribution of polluted weather types and clean weather types,according to the location of the 850hPa Lanzhou area relative to the weather system,the nine polluted weather types are subjectively summarized as saddle field,low pressure type and high pressure east type.It is also found that when 700hPa and 850hPa wind fields are dominated by westerly and southerly winds,polluting weather is prone to occur;the four clean weather types can be summarized as the rear of the cold front.The Lanzhou area is mainly affected by the high-pressure area,and the northerly winds are the main ones.?5?Research on the correlation between different meteorological parameters and particle concentration found that:the correlation between the 10-meter wind speed,the height of the boundary layer and the ventilation coefficient and the particle concentration in the heating period is high,and there is a negative correlation.When the wind speed is large and the height of the boundary layer increases,there is conducive to the diffusion and dilution of atmospheric particulate matter.?6?By analyzing the circulation situation of two cases of polluted weather during the heating period in Lanzhou from 2017 to 2018,the rationality and applicability of the weather classification results of this study in Lanzhou were tested.