The Changing Of Air Quality Influenced By Reducing The Pollutants Discharging From The Coal-fired Power Plants During Winter In Lanzhou City

"Winter prevention"and"heavy pollution weather prevention"are the important contents of Lanzhou city governmentundefineds work of preventing and controlling air pollution.In order to explore the effect of pollution sources on the ambient air quality of Lanzhou main urban area after various enterprises adopt emission reduction measures,the paper takes the emission reduction measures in Lanzhou Air pollution Emergency Preparedness Plan as a reference.This paper probes into the influence of four thermal power plants on ambient air quality before and after emission reduction in the main urban area of Lanzhou during winter prevention.The technical route of this paper is as follows:（1）Based on the monitoring data of environmental quality from 2015 to 2016 in five state-controlled sites in Lanzhou,the characteristics of environmental quality in the region and its main influencing factors are analyzed and studied.（2）Taking the emission reduction measures in Lanzhou Air pollution Emergency Preparedness Plan as the reference,setting up the uncut scheme,the first-level reduction scheme and the second-level reduction plan,respectively,to explore the diffusion law and distribution characteristics of pollutants in different schemes during winter control.The change of pollution contribution and absolute reduction ratio of the subjects to the four national control points before and after the reduction were compared and analyzed,and the effects on the environmental air quality after the implementation of the reduction program during winter control were analyzed.By using ArcGISand the distribution of Lanzhou administrative region,the variation of the contribution of pollutants to each region before and after the source intensity reduction was analyzed during winter control.（3）Taking the ambient air quality monitoring data of the state-controlled points as the background value,using the CALPUFF model to simulate the effects of the objects on the environmental extinction coefficient and the visibility change around the control points,and using ArcGIS-combined with the simulation results of the visibility.The changes of extinction coefficient and visibility of each region in each scheme are compared and analyzed.The main findings include:1)the time distribution of pollutants such as SO₂、NO₂、CO、PM₁₀、PM_2.5 were affected by seasons,all of them were"low in summer and autumn,high in winter and spring".The characteristics of"southwest high"are that the daily mean of AQI index、SO₂、NO₂、CO、PM₁₀、PM_2.5 in the four national control points in the winter control period of 2015²016 basically shows the trend of"inverted U type".（2）According to the results of CALPUFF simulation,the pollutants emitted during winter control were transported along the northwest to southeast direction,and the highest value was located in Xigu area.The contribution of SO₂、NO₂、PM₁₀0 and PM_2.5 to national control points decreased under different reduction schemes.Among them,"Lanlian Hotel","Zhigong Hosipital"and"Tielushejiyuan"had obvious reduction effects.The effect of reduction of NO₂and SO₂ is especially obvious after the default scheme,and the reduction of NO₂ and SO₂ is more obvious.The contribution of NO₂ emission to the concentration of Lanlian Hotel was reduced by 8.09%and 15.37%respectively,the contribution of SO₂ to the concentration of SO₂ was reduced by 7.67%and 12.81%,respectively.The concentration contribution of each pollutant in Xigu area is relatively large.（3）Before and after the reduction,the state control points at the Lanlian Hotel are all the national control points with the highest extinction coefficient and the lowest visibility level among the 4 state-controlled points.After the reduction of the plan2 and the plan3,the extinction coefficient at the state control points in all countries has been reduced,and the visibility level has been improved.The average extinction coefficient of Lanlian Hotel during the period decreased to 319.9km^-1 and295.56 km^-1.The visibility level in Anning District was high in combination with the administrative division of the main urban area of Lanzhou and its geographical location.The mean value of visibility in Anning area increased to 12.31 km during the visibility period.