Abstract
With the rapid development of China’s economy and industry, characterizing the spatial and temporal changes of aerosols in China has attracted widespread attention from researchers. The national-level urban agglomerations are the most concentrated areas of China’s economic, population and resource. Studying the spatial and temporal changes of aerosol optical depth (AOD) in these regions has practical guiding significance for effective monitoring of atmospheric particulate pollution. This paper analyzed the spatial and temporal variations of AOD in China’s urban agglomerations during 2001–2017 by using Terra Moderate resolution Imaging Spectroradiometer (MODIS) Collection 6.1 (C6.1) Level 2 aerosol products (MOD04_L2). Five national-level urban agglomerations were chosen: Yangtze River Delta (YRD), Pearl River Delta (PRD), Beijing-Tianjin-Hebei (BTH), Yangtze River Middle-Reach (YRMR) and Cheng-Yu (CY). We analyzed the change patterns of AOD in different urban agglomerations at multi-time scales and built a time series decomposition model to mine the long-term trend, seasonal variation and abnormal change information of AOD time series. The result indicated that averaged AOD values in the five urban agglomerations were basically increased first and then decreased at the annual time scale during 2001–2017. The averaged AOD showed strong seasonal differences and AOD values in spring and summer were typically higher than those in autumn and winter. At the monthly time scale, the AOD typically varied from low in cold months to high in warm months and then decreased during the rainy periods. Time series decompositions revealed that a notable transition around 2007–2008 dominated the long-term overall trend over the five selected urban agglomerations and an initial upward tendency followed by a downward tendency was observed during 2001–2017. This study can be utilized to provide decision-making basis for atmospheric environmental governance and future development of urban agglomerations.
Highlights
Atmospheric aerosols are solid or liquid particles that are suspended in the air
Aerosols can reduce the amount of solar radiation and sunlight reaching the ground by absorbing and scattering solar radiation, thereby responding to the Earth’s radiation balance [3]
The main goal of this study is to provide a reference for understanding the spatial and temporal change patterns of atmospheric aerosols over these highly urbanized areas
Summary
Atmospheric aerosols are solid or liquid particles that are suspended in the air. Atmospheric aerosols have great spatial and temporal variability and their distribution characteristics have a significant influence on the formation of cloud and precipitation [1,2]. Aerosol particles can act as cloud condensation nuclei to affect the optical properties of the cloud, the amount of clouds and the lifetime of the cloud, thereby affecting precipitation and water cycles [4,5]. The monitoring of the spatial and temporal distribution of aerosols has been used as an important basis for accurately assessing the climatic effects of aerosols [8,9] and the impacts of aerosols on air quality [10]
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