Spatio-Temporal Variation in AOD and Correlation Analysis with PAR and NPP in China from 2001 to 2017

Abstract

Atmospheric aerosols can elicit variations in how much solar radiation reaches the ground surface due to scattering and absorption, which may affect plant photosynthesis and carbon uptake in terrestrial ecosystems. In this study, the spatio-temporal variations in aerosol optical depth (AOD) are compared with that in photosynthetically active radiation (PAR) and net primary productivity (NPP) during 2001-2017 in China using multiple remote sensing data. The correlations between them are analyzed at different scales. Overall, the AOD exhibited a northeast-to-southwest decreasing pattern in space. A national increasing trend of 0.004 year −1 and a declining trend of −0.007 year −1 of AOD are observed during 2001-2008 and 2009-2017. The direct PAR (PAR dir ) and diffuse PAR (PAR dif ) present consistent and opposite tendency with AOD during two periods, respectively. The total PAR (PAR total ) shows a similar variation pattern with PAR dir . In terms of annual variation, the peaks of AOD coincide with the peaks of PAR dif and the troughs of PAR dir , indicating that aerosols have a significant positive impact on PAR dir and a negative impact on PAR dif . Furthermore, the PAR dir has a stronger negative association with AOD than the positive correlation between PAR dif and AOD at national and regional scales, indicating that PAR dir is more sensitive to aerosol changes. The NPP has higher values in the east than in the west and exhibits a significant increasing trend of 0.035 gCm −2 day −1 after 2008. The NPP has a negative correlation (−0.4-0) with AOD and PAR dif and a positive correlation (0-0.4) with PAR dir in most areas of China. The area covered by forests has the highest NPP-PAR correlation, indicating that NPP in forests is more sensitive to the PAR than is the NPP in grasslands and croplands. This study is beneficial for interpreting the aerosol-induced PAR impact on plant growth and for predicting plant production on haze days.Many studies have been conducted in terms of the spatio-temporal variations in AOD in different scales and time periods over the past decades. He, et al.[5] studied the AOD trend in China during 2002-2015 and analyzed the impact factors including terrain, vegetation and socio-economic indices. That study showed an increasing trend in AOD during 2002-2007 and a decreasing trend during 2008-2015. In addition, AOD was found to have a weak relation with NDVI and a strong relation with elevation and population. Wang, et al. [6] calculated the trend in AOD in north China in the period of 2001-2016 and found various trends in different regions. By using MODIS and MERRA-2 datasets from 1980 to 2017, Qin, et al. [7] found an increasing trend in southeastern China and a decrease trend in northernmost China. That study also showed that the dust and SO 4 are the main constituents of aerosols. et al. [8] analyzed the AOD trend over the global ocean during 2000-2015.Results showed AOD has a trend of 0.002 decade −1 and is highly correlated with shortwave aerosol radiative effect (SWARE), which ...

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