Publications

Gupta, G; Ratnam, MV; Madhavan, BL; Narayanamurthy, CS (2022). Long-term trends in Aerosol Optical Depth obtained across the globe using multi-satellite measurements. ATMOSPHERIC ENVIRONMENT, 273, 118953.

Abstract
Although trends in the Aerosol Optical Depth (AOD) have been examined broadly but the effects due to the prevailing background conditions on these still remain uncertain, for which a multivariate regression trend model has been implemented in this study. Long-term AOD trends across the globe are obtained from the multi satellite measurements that include MODerate resolution Imaging Spectral-radiometer (MODIS on-board Terra (T) and Aqua (A), between 2001 and 2020), Multi-angle Imaging Spectral-Radiometer (MISR, 2001-2020), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP, 2006-2020) observations using both the linear as well as multivariate regression analysis. Before evaluating the trends, a detailed comparison has been made with the ground-based AEronet RObotic NETwork (AERONET) observations (2001-2020) obtained from more than 80 stations covering the globe. A high (above 0.7) to medium (from 0.3 to 0.7) spatial correlation is noticed among all the satellite measurements except the CALIOP (over a few sites) observations. However, MISR (CALIOP) observed AOD values underestimated (overestimated) with that measured by the AERONET AOD over the high aerosol loaded regions. In addition, Modern-Era Retrospective analysis for Research and Application version-2 (MERRA-2) AOD dataset is also able to simulate the mean as well as trend values across the globe. A decreasing trend in AOD is mostly seen in connection with the implementation of emission control policies (Eastern North America, Europe, and Eastern and Central China), reduction in forest fires (South America), and the stilling of surface winds over arid regions (Western North Africa). On the other hand, AOD trends perceived over the South Africa region have increased in comparison to the values reported earlier. Surprisingly, the CALIOP sensor has shown a rather significantly decreasing trend values over the Middle-East region. When compared, the region-wise linear regression trend analysis declined to give any statistically significant values over huge aerosol variability regions such as North Africa, South Africa, Middle-East, China, and the Indian regions. These robust findings will form a firm basis to evaluate the dependence of physical and chemical characteristics of aerosol on the observed AOD trends so that the impact of varied aerosols emission sources can be quantified accurately across the different regions.

DOI:
10.1016/j.atmosenv.2022.118953

ISSN:
1873-2844