Study On The Influence Of Landscape Pattern Change On PM_2.5Concentration In Yangtze River Delta

The haze pollution caused by PM2.5 has posed a serious threat to human health and social sustainable development,and has become a common problem faced by China's rapidly developing areas.Most of the research on air pollutants has sought technical and management methods to control urban air pollution,and less to investigate the effect of urban landscape pattern changes on air pollutants.The Yangtze River Delta(YRD)is one of the fastest urbanization processes and the most serious air pollution regions in China,so it is helpful to make a reasonable allocation of the "source" and "sink" landscape pattern of PM2.5 that exploring the influence of land use landscape pattern and urban form on PM2.5 concentration in this area,providing scientific reference for pollution prevention and control.Using the methods of gravity model,cold-hotspot analysis,landscape pattern index and urban form index,this research investigated the spatiotemporal distribution characteristics of PM2.5 concentration in YRD for 1995-2015,and explored the evolution of land use landscape pattern and urban form.In addition,we also used the ridge regression model to analyze the effects of landscape pattern of four land use types(including built-up area woodland,cropland,and water body)on PM2.5 concentration at multiple spatial scales,as well as the influence of urban morphology on the PM2.5 concentration across three city size groups,giving corresponding suggested measures for mitigating air pollution.The conclusions reached are as follows:(1)The PM2.5 concentration has increased significantly from 1998 to 2015,leading the proportion of air quality standard areas decreased,especially in 2007,2008,2013 and 2015.Spatially speaking,the PM2.5 concentration of inland area is greater than the coastal region.Moreover,the urban haze pollution in the north was generally more serious than that measured in the southern regions of the YRD,reflecting obvious spatial agglomeration phenomenon.Furthermore,by using the global spatial autocorrelation index method,the spatial correlation of the PM2.5 decreases significantly when the distance between the two cities is greater than 300km,and tends to be 0 at 450km.(2)The built-up area is the most important "source" landscape type of PM2.5,the proportion of which has increased greatly during the study period,and the aggregation degree has been improved,forming a continuous landscape.Woodland is the main "sink"landscape type of PM2.5,and its proportion in the research period is declining.Cultivated land has a staggered effect on the "source" and "sink" of PM2.5,and its proportion decreases the most in the research period,and the phenomenon of landscape fragmentation deepens,and the landscape heterogeneity increases.(3)Compared with the administrative scale,the negative correlation between the concentration of PLAND,ED and PM2.5 in woodland at the circumscribing circle scale is more significant,and it can be seen that the optimization of landscape pattern in the surrounding area of the city is more favorable to play its role in reducing particulate matter.Controlling the reasonable and orderly growth of built-up area and adopting the polycentric development mode are beneficial to relieve the environmental pressure in the main urban area;improving the proportion and aggregation degree of woodland in the surrounding area of the city,or increasing the contact area between woodland and construction land can effectively reduce urban PM2.5 concentration;organizing the cropland to form a continuous landscape,and reduce the PM2.5 precursors brought about by agricultural production on cropland through scientific farming methods,which is helpful to play its role of "sink" to PM2.5.(4)Along with the process of urban expansion,most of the Yangtze River Delta cities have also undergone significant changes in their urban form.The majority of urban separation increased and the fragmentation decreased,it can be seen that the internal and epitaxial expansion of the study period as the main urban expansion model,the city's urban core of the dominant degree has been expanding,the annexation of its surrounding broken plaque.The compactness index is a depiction of the shape of the city,and the lower its value,the narrower the shape of the city's urban core.During the research period,the compact size of small cities in the Yangtze River Delta mostly has an upward trend,while the compactness of medium-sized cities is mostly decreasing,and the compactness of large cities has not changed significantly.(5)The influence of urban form on PM2.5 concentration varies according to the size of the city.The explanatory powers of urban form on PM2.5 concentration were 63.9%,61.7%,and 48.9%for the small,medium,and large cities,indicating that the influences of urban form on PM2.5 concentration will diminish as the size of the city increases.For small and medium cities,the use of leapfrog expansion,development of satellite towns,supporting for township development is a powerful means to improve air quality.For large cities,optimizing the compactness of the main city and opening up the multi-center of the city is its effort.