Performance of MODIS C6.1 Dark Target and Deep Blue aerosol products in Delhi National Capital Region, India: Application for aerosol studies

Delhi National Capital Region (NCR) of India is one of the most polluted regions in the world, yet only two ground-based monitoring sites under the AEROsol RObotic NETwork (AERONET) measuring Aerosol Optical Depth (AOD) are operational in this region. Here, we assessed the performance of Terra and Aqua MODIS collection 6.1 AOD product to understand their applicability for studying seasonal and spatial variations of AOD over Delhi-NCR. We compared Deep Blue AOD at 550 nm retrieved at 10 km resolution (DB10K), and Dark Target AOD retrieved at 3 km (DT3K) and 10 km (DT10K) resolutions against AOD from these two AERONET sites (Gual Pahari and Amity University) during 2010-2019 keeping in mind the uncertainty range represented as expected error (EE) envelope [EE = + (0.03 +/- 20% AOD(AERONET)) for DB10K, EE = +/- (0.05 + 20% AOD(AERONET)) and EE = +/- (0.05 + 15% AOD(AERONET)) for DT3K and DT10K respectively]. Our evaluation reveals the following statistics: correlation coefficients (R) of 0.44, 0.74, and 0.77 for DB10K, DT3K, and DT10K AODs from TERRA and 0.7, 0.79, and 0.72 from AQUA, respectively and root mean square errors of 0.26, 0.01, and 0.17 for AODs from TERRA and 0.24, 0.20, and 0.24 for AODs from AQUA, respectively. Our results demonstrate better reliability of the DT AOD products relative to DB over urbanized areas in North India. Emission from industries, power plants, brick kilns, enhances aerosol loading after a light precipitation event.

Automated summary

The study assessed the performance of Terra and Aqua MODIS collection 6.1 AOD product in studying seasonal and spatial variations of AOD over Delhi-NCR. The evaluation revealed better reliability of Dark Target AOD products relative to Deep Blue AOD over urbanized areas in North India.