Impact Of The Sloping Land Conversion Program On PM_2.5 In Shaanxi Province

The Sloping Land Conversion Program（SLCP）is an ecological project initiated by the state with the largest scale,the highest participation and the largest amount of investment.It has been implemented for more than 20 years until 2020.As an effective policy and means to restore forest vegetation,the Sloping Land Conversion Program has played an important role in water conservation,carbon sequestration,oxygen release,atmospheric environment purification and biodiversity protection by planting trees according to the principle of suitable land and suitable trees.As one of the pilot provinces of the project of the Sloping Land Conversion Program,Shaanxi Province has completed the assignment of the Sloping Land Conversion Program of 1.241 million hectares by 2018,ranking the first in the country.And the forest coverage rate in this stage has also become the largest and fastest growth period in history.At the same time,the Shaanxi Provincial Ecological Environment Bulletin shows that PM_2.5pollution has been significantly improved since 2005.In addition,the study confirmed that the relationship between vegetation and PM_2.5 would be affected to a certain extent due to the limitation of climatic conditions such as temperature and precipitation in different regions.Shaanxi climate conditions exist obvious regional differences,so in global climate warming trend and increase forest coverage has been promoted to improve the air quality of background,a reasonable assessment of climate change under the condition of the Sloping Land Conversion Program in reducing the effectiveness of PM_2.5 pollution will help China’s air pollution under control and the development of a new round of the Sloping Land Conversion Program.At first,this paper analyzed and summarized the the domestic and foreign research progress on PM_2.5 pollution and the Sloping Land Conversion Program and finded out the shortcomings of the existing studies on the evaluation of the effect of reducing haze.Finally,the paper determined the research entry point and combine the existing theoretical basis.Considering the spatial dependence of PM_2.5 pollution and vegetation cover,based on the existence of spatial correlation determined by Moran’s I index,an appropriate spatial econometric model was selected by using LM test,and the spatial panel regression model was used to quantify the relationship between the conversion of farmland to forest and PM_2.5pollution by integrating social and economic factors and natural environment factors.Finally,two main meteorological factors,precipitation and air temperature,were introduced as regulating variables to further explore whether and how different air temperature and precipitation conditions would affect the relationship between conversion of the Sloping Land Conversion Program and PM_2.5 concentration.Through the empirical analysis,the verdicts are as follows:（1）The Sloping Land Conversion Program effectively promoted the increase of cultivated land to forest land in Shaanxi Province.The increased rate of transition from cultivated land to forest achieved the fastest from 2000 to 2005 and the increased rate tended to be stable from 2005 to 2010.From the perspective of regional distribution,the effect of the Sloping Land Conversion Program in northern and southern Shaanxi is more obvious than that in Guanzhong.（2）From 2000 to2005,2005 to 2010and 2010 to 2015,the percentage of counties with PM_2.5 pollution level continuously increasing showed the trend of first increasing and then decreasing.In addition,the increasing PM_2.5 pollution levels showed different degree of agglomeration distribution in the three regions of southern Shaanxi,northern Shaanxi and central Guanzhong.From 2000to 2015,the percentage of counties with decreasing PM_2.5pollution levels of the total accounted for more than 80%,mainly in northern and southern Shaanxi.The main decreasing trend was concentrated in northern Shaanxi during 2000-2005,and the main decreasing trend was concentrated in some areas of southern Shaanxi and central Guanzhong during 2005-2010.（3）Without considering the meteorological factor regulation under the premise of cumulative increase of returning farmland to forest of the county can not only effectively reduce its PM_2.5 pollution level,and can effectively reduce PM_2.5 pollution level of the adjacent counties.The calculation results of Spatial Durbin Model showed that when the area of conversion of farmland to forest increases by 1 unit,its PM_2.5 concentration decreases by0.084 units on average and the PM_2.5concentration in its neighboring counties decreases by0.719 units.（4）Theaverage annual temperature of meteorological factor had a positive moderating effect on the PM_2.5 concentration in the county.When the county’s temperature increased by 1 unit,the negative marginal contribution of the mean annual PM_2.5 concentration in its county decreased by 0.001 unit on average.However,the average annual precipitation of meteorological factor did not have a significant regulating effect on the effect of the Sloping Land Conversion Program on PM_2.5concentration,that is,the difference of precipitation conditions between regions in Shaanxi Province will not have a significant impact on the relationship between the Sloping Land Conversion Program and PM_2.5 concentration.