Spatio-Temporal Changes Of AOD And Meteorological Influencing Factors In Beijing-Tianjin-Hebei Region

The Beijing-Tianjin-Hebei Region is one of Chinese heavy industry bases,but the rapid industrial development brought serious air pollution.At the same time,the northern part of Beijing-Tianjin-Hebei borders the North China Plain and Inner Mongolia,therefore,the Northern BTH Region is vulnerable to sand and dust weather.The establishment of the Three-North Shelterbelt and the publish of air pollution prevention and control regulations have brought air pollution under control,but the problem of air pollution in the BTH Region is still serious.Aerosol optical depth(AOD)is the integral of the aerosol extinction coefficient in the vertical direction,which is an important indicator for evaluating air quality.Exploring the temporal and spatial evolution of AOD and its correlation with meteorological factors has important guiding significance for regional atmospheric control.Based on the MODIS MOD04 dataset and MCD19A2 dataset from 2001 to 2020,this thesis adopt linear regression analysis,empirical orthogonal function decomposition(EOF),potential source contribution factor(PSCF),iterative self-organizing data analysis technology algorithm(ISODATA)and geographic detector,to analyze spatial-temporal distribution and evolution trend of AOD in the BTH Region from multiple time scales.At the same time,in order to explore the effect of strong wind on aerosols,select Chengde City as the research object,and the HYSPLIT model was used to analyze the characteristics of aerosol transport.Based on different spatial scales,the influence of meteorological factors on AOD was discussed.The specific conclusions are as follows:(1)Based on the MODIS MOD04 and MCD19A2 data sets,this thesis construct the AOD fusion data set using the Multi-Angle Atmospheric Correction(MAIAC)priority method.The ground station data verification results show that the correlation coefficient and error pass rate between the fusion daily data set and the measured value meet the requirements given by NASA,and the correlation between the fusion monthly data set and the measured value is stronger than that of the MOD04 and MCD19A2 data sets,indicating that the fusion data sets is applicable in the BTH region.(2)The AOD in the study area showed a fluctuating upward trend from 2001 to2014,and began to decline gradually since 2015;the spatial distribution is characterized by high in the south and low in the north,with a significant downward trend as a whole,and the most significant decline in the northwest Region;there are mainly global consistent types and north-south differentiation.The value and fluctuation range of AOD in summer are the largest,ranging from 0.45 to 0.75;AOD shows a significant downward trend,and the decline is more obvious in northern Hebei.The range of AOD are similar in spring,autumn and winter,which between 0.3 and 0.5,and the change trend was not significant.(3)The analysis of the transport characteristics of foreign aerosols shows that the airflow has strong influence on AOD,which not only transmits foreign aerosols,but also causes aerosol accumulation,making it difficult for aerosols to diffuse.The analysis of seasonal transport characteristics shows that the distribution of potential pollution sources in Chengde City is related to the monsoon climate.The southern Hebei Region and the Northeast Plain are the main potential pollution sources in spring and summer;Loess Plateau,Inner Mongolia and Mongolia are the main potential pollution sources in autumn and winter.(4)The correlation between AOD and meteorological factors is analyzed from overall perspective.The geographic detector shows that the temperature and pressure in the BTH Region are highly correlated with AOD,while temperature and humidity are the dominant interaction factors.Based on the Pearson correlation coefficient method,air temperature is positively correlated with AOD,while air pressure is negatively correlated with AOD,and the higher the air pressure,the higher the correlation between air pressure and AOD.Based on ISODATA,the BTH Region is divided into area 1,area 2 and area 3,and geographic detection is carried out on the annual scale and monthly scale.The annual scale results show that the dominant factors of Region 1 are temperature and air pressure,and the dominant factors of Region 2 is temperature and humidity,while the dominant factors in Region 3 are temperature and humidity.The monthly-scale results show that the difference in the contribution rate of meteorological factors between different regions is mainly affected by the terrain,while the difference in the contribution rate between different months is due to the influence of the monsoon climate.