SPATIAL-TEMPORAL CHARACTERISTICS OF THE AEROSOL OPTICAL DEPTH (AOD) DERIVED FROM LONGTERM (1980–2018) MERRA-2 OVER GUANGDONG
This paper presents and compares the aerosol optical depth (AOD) spatial-temporal characteristics over five subsets in different locations of Guangdong, as well as Hong Kong and Macau (GDHM) since reform and opening-up. By means of GIS analysis tools and subset the onward MERRA-2 monthly mean value aerosol reanalysis dataset to the size of study area, the results reveal that the yearly mean AOD over the whole GDHM ranged from 0.18 to 0.69 during 1980 to 2018. The field average of AOD in five chosen areas approached to 0.40 and appeared linearly increased at 0.0077 per year. All the five selected areas reached their yearly mean AOD peaks at 2007. The field average AOD increased rapidly at 0.028 per year from 1997 till 2007 then appeared decreasing oscillation in a linear slope −0.0109 per year since 2007. But the average AOD of 2010–2018 is higher than the former three decadal averages. Comparing the former and the latter two decades, the high yearly mean AOD value clusters have moved from northern parts of Guangdong to central north Pearl River Delta, where also appeared more apparent AOD yearly change among the other three parts since late 1990s. Only six yearly mean AOD over southern cities of Pearl River estuary were lower than east or west comparing parts in 1980s. Eastern part of Guangdong stayed the lowest yearly mean AOD region in 21years of the past 39 years. Central, southern and western of GDHM had 36 years while northern and western of GDHM had 37 years their AOD values during February to April were the high values of the year.