Abstract:

The Beijing-Tianjin-Hebei region, which is located in the Bohai Rim, is the most economically developed region in northern China. It is also one of the most polluted regions in China. Aerosol optical depth (AOD) can effectively reflect the degree of air pollution. In this study, the MODIS 3 km AOD remote sensing data was analyzed and the research results would be of great significance to China’s air pollution. Firstly, the temporal variation characteristics and spatial autocorrelation characteristics of AOD in Beijing-Tianjin-Hebei region from 2010 to 2016 were analyzed. The factors of precipitation, wind speed, relative humidity, normalized difference vegetation index (NDVI),gross domestic product (GDP),secondary industry GDP, population density were selected as the affecting factors of AOD, using geographical detection to analyze the trend of the factors contribution ratio and its dominant affecting factors in different regions and different times in Beijing-Tianjin-Hebei region. The results showed as follows: (1) The annual average AOD of the Beijing-Tianjin-Hebei region was 0.83 from 2010 to 2016.The annual average AOD of Tianjin was the highest in the study area, followed by Hebei and Beijing. The annual variation trend of AOD was shown an overall state of decline first followed by rise and then a small fluctuation change and a similar status in each local region as well. (2) The spatial autocorrelation analysis indicated a significant positive correlation among spatial distribution of AOD in Beijing-Tianjin-Hebei region. Local high-accumulation areas were mainly concentrated in the southeastern part of Beijing, southern part of Tianjin, and central-southern part of Hebei Province. The low-accumulation areas were concentrated in the mountains of the northwest. The area of the high and low accumulation areas in Beijing-Tianjin-Hebei region showed a decreasing trend, while the area of the non-significant areas showed an increasing trend. (3) Geographic detection analysis indicated that the primary influencing factor was NDVI in Beijing, followed by population density, and their interaction was significant. The dominant factor was wind speed in Tianjin. The effect of human factors such as population density and the GDP of the secondary industry were also important. The effect of interactions between wind speed and the above factors were also significant. The dominant factor was population density in Hebei Province, followed by GDP and the secondary industry’s GDP, and the overall interaction was relatively weak. In the past, the correlation analysis of the influencing factors was based on linear relationship of the overall area, while the geographical detection not only has wireless assumptions, but also reveals the linear, nonlinear and spatial relationships of the driving factors. From this perspective, the geographical detection is more reliable in studying the influencing factors. This study applied geographical detection to analysis of the impacting factors of AOD in Beijing-Tianjin-Hebei region, which proved its feasibility in this field and this region. At the same time, the results also had important reference value for air pollution prevention, industrial and agricultural layout and urban construction in Beijing-Tianjin-Hebei region.

Key words: aerosol optical depth (AOD), spatial-temporal variations, geographical detection, influencing factors, Beijing-Tianjin-Hebei region