| The progress of China’s urbanization has achieved remarkable achievements,but at the same time it has also caused serious environmental pollution problems.The most harmful problem of pollution is air pollution,and air pollution is mainly haze.Haze has seriously affected people’s normal life.As a major component of smog,PM2.5 has become the focus of government and society.Under the advocacy of the country’s proposal that "lucid waters and lush mountains are invaluable assets",how to promote urbanization health is gradually becoming a hot spot.Therefore,it is necessary to strengthen the three-dimensional distribution characteristics and influencing factors of urban PM2.5 high-incidence period（winter）,which can not only provide guiding reference for targeted prevention and control of haze,but also more scientifically assist urban planning.It has certain practical significance in practical applications.This paper takes Beijing as the research area,and the time span is 2017 winter（December 2017-February 2018）.The geographically weighted regression method is used to estimate the PM2.5 concentration of the treated MOD043K aerosol product,using CALIPSO data.The extinction coefficient and the attenuation backscattering coefficient are used to qualitatively evaluate the PM2.5 distribution in vertical high altitude,and the three different dimensional characteristics of PM2.5 concentration in horizontal spatial distribution,vertical spatial distribution and time distribution are studied,and the natural detector is used to quantitatively analyze the nature.The influence of factors and human factors on the distribution characteristics of PM2.5 concentration.The research work carried out in this paper is as follows:（1）Interpolating the MOD043K aerosol products in Beijing area by using ordinary Kriging and natural proximity interpolation,respectively,to obtain the aerosol optical depth distribution results covering the whole Beijing,and two Interpolation results weighted fusion,cross-validation of the final acquired AOD and ground-based AERONET data;（2）Estimation of horizontal PM2.5 concentration by AOD using geographically weighted regression model,and the accuracy of the estimation was verified by comparing the data of the ground environmental monitoring stations,analysis of spatial levels Distribution characteristics and distribution changes in different time units;（3）The extinction coefficient and attenuation backscattering coefficient are calculated by using CALIPSO data,and the vertical profile of extinction coefficient and the distribution of vertical air pollution are obtained.According to the extinction coefficient,there is a linear proportional relationship between extinction coefficient and PM2.5 concentration.The attenuated backscattering coefficient can distinguish the characteristics of polluted aerosols from those of clean aerosols,and indirectly evaluate the temporal and spatial distribution of PM2.5 in vertical space;（4）The effects of natural factors（wind speed and wind direction,vegetation coverage）and human factors（road network,population activities and buildings）on the evolution of PM2.5 concentration distribution in horizontal and vertical space in Beijing were quantitatively analyzed by geographical detector.The wind speed and wind direction are extracted from 10 m near the ground and 500hPa potential height（the average altitude is about 5500m）by ECMWF remote sensing data.Draw the following conclusions:（1）The AOD effect after filling the reflectivity statistical model is better,and the cross-validation accuracy of the ground-based AERONET data is higher,which proves that the reflectivity statistical model can effectively fill the AOD missing area,which has good universality and reliability,and the filling efficiency is high.AOD estimates the level of PM2.5 concentration based on the geographically weighted regression model with high accuracy.The correlation between the estimated value and the measured value reaches 0.779,which basically meets the experimental requirements.The estimation error mainly comes from the cumulative propagation of error and the limitation of model algorithm.（2）The distribution of PM2.5 level in winter in Beijing in 2017 showed that the high concentration of PM2.5 was mainly concentrated in the southeast plain,and the concentration of PM2.5 was the lowest in most parts of northwest and small parts of northeast China.The concentration of PM2.5 in southwest and southeast of the ring is between high and low values.In December,the high concentration range of PM2.5 concentration was concentrated in the southeast,the sub-high concentration buffer zone appeared in the southern part of the ring,and the high concentration range decreased in January.The highest value region shifted from southeast to south,and the range of high PM2.5 concentration expanded from southeast to southeast in February,with local and northwest parts of northeast China.The vertical distribution is mainly manifested in 1～4km.The vertical distribution of PM2.5 along the longitudinal section from south to north is characterized by the increase of latitude,the vertical distribution of PM2.5 increases at first and then decreases with the increase of latitude.40.18°N is the turning point of the vertical distribution between the north and the south of PM2.5 in Beijing,while Beijing is the turning point of the vertical distribution of PM2.5 over the north and south of China at the same longitude.The profile of extinction coefficient and the attenuation backscattering coefficient are stable in December,and vary in varying degrees in January and February.（3）Wind speed and wind direction are one of the natural factors affecting PM2.5 diffusion in Beijing in winter.The wind direction of 10m near the ground or the height of 500hPa potential is northwest wind.The influence of 10m wind speed near the ground on PM2.5 distribution is greater than that of 500hPa potential height wind speed on PM2.5 distribution,and the relationship between 10m wind speed near ground and PM2.5 is negatively correlated.The relationship between 500hPa potential height wind speed and PM2.5 is that PM2.5 decreases with the increase of wind speed in a certain range,beyond which PM2.5 increases with the increase of wind speed.Vegetation pairs in different regions,the influence of PM2.5 distribution is great,and the dense vegetation with low coverage in urban area will be difficult to dissipate because of the influence of location.The vegetation outside the urban area,especially in the northern mountain area,has many varieties and high coverage,and is affected by location.The adsorption of PM2.5 by vegetation is greater than that of hindering the diffusion of PM2.5.（4）Ranking of the driving forces of population activity impacts calculated by the geo-detector is the Road Network Density（0.4967）>Parking（0.0753）>Park（0.0484）>Life Service（0.0401）>Restaurant（0.0344）>Company（0.0258）>Hotel（0.0220）.It is known that urban population activities have a greater impact on the distribution of PM2.5.The traffic road network and parking lot of population activities have the greatest driving force for PM2.5 distribution,and the driving force of traffic road network is 7 times that of parking lots There is a positive correlation between the relationship with PM2.5 concentration.The total driving force of the remaining population activities POIs and the PM2.5 concentration relation is more than 0.02,indicating that the remaining population activities POIs have a certain effect on the distribution of PM2.5.（5）Exhaust pollution caused by traffic lines with high density of road network is the main factor affecting PM2.5 distribution.The influence of unreasonable building layout on PM2.5 distribution is reflected in building density and height difference,high density.Low-rise and high-rise buildings tend to form building“canyons",and PM2.5 is not easy to dissipate.Low-density super-tall buildings have limited impact on PM2.5 distribution.Dense multi-story and sparse middle and high-rise buildings have PM2.5 distribution.A certain influence,but the layout is reasonable to avoid the formation of a building "canyon".（6）The low-rise and high-rise buildings with high density in the city center are planned around the tuyere location as far as possible,and the building height outside the tuyere location should be reduced as far as possible,and away from the high-traffic roads such as high-speed and national roads,especially at intersections.The building orientation of the intersection area does not affect the flow of airflow,which can evacuate PM2.5 emissions from vehicles in urban central streets.High-density low-rise,high-rise buildings can be planted on the street side of the road to plant a moderate amount of low-calorie evergreen vegetation,and it is best to choose an evergreen coniferous forest with better adsorption effect on PM2.5. |
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