An Empirical Study On The Spatiotemporal Variation Of PM_2.5 And Its Relationship To Land Use In China

At present,China is in the process of rapid development of urbanization.Land use changes are significant.Through emissions or absorption and changes in hydrothermal conditions,land use will inevitably affect the spatial-temporal changes of PM_2.5.Therefore,improving air quality through optimizing land use patterns has important practical significance for promoting the coordinated development of social economy and ecological environment.Based on the 2000-2015 Global Estimates?V4.GL.02?PM_2.5 dataset and 2016 site monitoring PM_2.5 data,the correlation coefficient method,linear trend method,Ensemble Empirical Mode Decomposition?EEMD?,Detrended Fluctuation Analysis?DFA?,Multifractal Detrended Fluctuation Analysis?MF-DFA?,Exploratory Spatial Data Analysis?ESDA?,Mann-Kendall Trend Test,Rescaled Range Analysis?R/S?,Generalized Additive Model?GAM?and semi-parametric spatial econometric models are employed in this paper to analyze the characteristics of spatial-temporal changes of PM_2.5,the response relationship between PM_2.5 and land use,and the influencing mechanisms.The recommendations on land-use optimization for air quality improvement are proposed,with conclusions as below:?1?From 2000 to 2015,the average value of PM_2.5 in China was 35.36?g/m³,mainly between 10-35?g/m³.Over 61.05%to 74.28%of land area,PM_2.5 reached the requirements for the second-level limit?average of 35?g/m³ per year?of the ambient air quality standard?GB3095-2012?.In the area of 14.55%-21.57%of the country,PM_2.5 was lower than the criterion value of 10?g/m³ specified by the World Health Organization?WHO?.?2?PM_2.5 showed quasi-periodic oscillations of 3 hours,7 hours,and 14 hours on the hourly scale.On the daily scale,quasi-periodic oscillations of 1 day,3 days,7 days and 11-14 days,24-29 days and 90-365 days were shown.The characteristics of PM_2.5time-period changes exhibited certain time coupling with regional socio-economic activities.PM_2.5 emissions in the past had a certain impact on the current and future trends.?3?China is a region with a high concentration of PM_2.5 in the world,which clearly shows the phenomenon of concentrated regional convergence.The North China Plain,the Central Plains,and the Taklimakan Desert have formed large-scale high-pollution and concentrated areas,and they have maintained their sustained stability for a long time.From 2000 to 2015,PM_2.5 showed a significant upward trend in 12.68%of land area,which was concentrated in the central and western regions and North China,and only 2.36%of the national land area showed a significant decrease in PM_2.5,mainly in the southern coastal economic zone.In general,PM_2.5 was on the rise.?4?On the national scale,construction land and farmland were positively correlated with PM_2.5,and woodland,grassland,water bodies and unused land were negatively correlated with PM_2.5.On the regional scale,construction land and sandy land were positively correlated with PM_2.5,but farmland was positively correlated with PM_2.5 in a few areas,and woodland,grassland and unused land were negatively correlated with PM_2.5.In areas with high PM_2.5 values and well-developed shipping areas,water bodies were positively correlated with PM_2.5 and vice versa.?5?With the expansion of the construction land area,PM_2.5 is increasing.After reaching a certain scale,the development of urban construction can play a role in inhibiting PM_2.5 pollution.However,continuing to increase the scale of construction land will exacerbate PM_2.5 pollution.There is an environmental Kuznets curve in the impact of construction land on PM_2.5.The expansion of farmland will not only improve the level of PM_2.5 in this area,but will also enhance the PM_2.5 level in the neighboring areas and increase the overall regional PM_2.5.5 due to spatial spillover effect.On the contrary,the expansion of woodland and grassland area can not only inhibit the PM_2.5level in this area,but can also suppress PM_2.5 in the neighboring areas,so that the overall PM_2.5 is suppressed.Because of the small area of water bodies and unused land,they are easily affected by emissions from other land types,and it is difficult to separate out the true influencing mechanism on PM_2.5.?6?Reasonably controlling the scale of construction land in large cities and transforming the mode of urbanization of small and medium-sized cities,reducing the discharge of pollutants from cultivated land cultivation and increasing the proportion of woodland and grassland area have a positive effect on reducing PM_2.5.The impact of land use on PM_2.5 is actually determined by the nature of land use and the fundamental way to lower PM_2.5 is to reduce the amount of pollutants generated by human activities in the unit land area.