Satellite-based Retrieval Of Atmospheric Aerosol Optical Depth Of Hangzhou In The Past Decade

Using the daily MODIS data from 2003 to 2015 in Hangzhou City, a historical sequence of Aerosol Optical Depth (AOD) with 500m spatial resolution was inverted based on DDV method. After validation for inversion results combining with the ground observation data, the temporal and spatial distribution characteristics of AOD in Hangzhou were analyzed. A comparative analysis of the time series of AOD and Air Quality Index (AQI) of the city, and correction of vertical elevation and humidity for AOD were conducted. Finally, the research of correlation analysis between AOD and AQI was carried out before and after correction, respectively. The paper concludes the following conclusion:(1) The inversion result of AOD was validated by the ground observation from 3 sties. In the light of the correlation coefficients between monitoring AOD and the value of inversion were higher than 0.7 both in the 3 points, and absolute and relative error were 0.16,33% on average, respectively, the results showed that inversion was higher.(2) The temporal variation characteristics of AOD of Hangzhou was analyzed from 2003 to 2015. Although the annual average of AOD had a relatively slight fluctuation with the maximum in 2008 and the minimum in 2013, there were no significant trends both for raise and drop. The seasonal mean of AOD in spring and summer were higher than the value in autumn and winter. The monthly mean of AOD showed an increasing trend from Jan to Jun and the peaking point was observed in Jun. While the value dropped down in the next six months. The KZ wave filer was used to decompose the time series of AOD. The long-term component showed that the AOD of the city initially increased and then decreased in general terms, the value reached peak in 2008.(3) The distribution features of AOD in the city from 2003 to 2015 indicated that high value in northeast and low in southwest, and the highest were mainly located in the center of the city, while the secondary high value area were in Jianggan District and east of Yuhang District and Xiaoshan District. The area of higher values of AOD was increased firstly and then fell year by year. In terms of the distribution of seasonal AOD, the area of higher values in summer and spring were more than autumn and winter. The trend of distribution of AOD was analyzed based on MK method, the results showed that there was no significant change during the whole research period, but most areas of the city seen significantly increased for AOD from 2003 to 2008.(4) The overall air quality of Hangzhou was fine nearly two years. The air quality was featured by higher values of concentration for PM2.5 year-round and O3 in summer. The fluctuation of AOD agreed with AQI as a whole, and overall there was a positive correlation between the two ones, for which fluctuation feature almost match in summer half year. Meanwhile, the correlation coefficients between AOD and AQI greatly increased after correction.