Aerosol Measurements over India: Comparison of MAX-DOAS Measurements with Ground-based (AERONET) and Satellite-based (MODIS) Data

• Published in: Aerosol and Air Quality Research
• Main Authors: Prithviraj Mali, Mriganka Sekhar Biswas, Steffen Beirle, Thomas Wagner, Shrivardhan Hulswar, Swaleha Inamdar, Anoop S. Mahajan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2023
• Subjects: AOD; MAX-DOAS; MODIS; AERONET; Radiative forcing; Science; Q; Aerosol Robotic Network
• Online Access: https://doi.org/10.4209/aaqr.230076; https://doaj.org/article/101b6c0c52b24646a425c438f36c86bf

Abstract In this study, we present ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosols from two urban locations (Delhi and Pune) and one high-altitude rural location (Mahabaleshwar) in India. We utilized a profile retrieval algorithm to estimate the vertical profiles and vertical column densities of aerosols (AOD) using MAX-DOAS measurements of the oxygen dimer (O4) at ultraviolet and visible spectral regions. Our results from Pune show good agreement with the Aerosol Robotic Network (AERONET) observations at both UV and visible wavelengths, with correlation coefficients of 0.70 and 0.71, respectively. The MAX-DOAS retrieved AOD and the MODIS satellite-based AOD product at 360 nm for Pune and Mahabaleshwar showed similar variations with correlation coefficients of 0.70 and 0.74, respectively. However, over Delhi, the correlation was poor at 0.54. At 477 nm, all three locations had a moderately positive correlation between the MAX-DOAS and MODIS AODs, with statistically significant correlation coefficients of 0.66, 0.61, and 0.60, respectively. Over the high pollution regions, especially over Delhi, the MODIS AOD was systematically higher than MAX-DOAS AOD. The vertical profiles of aerosol extinction coefficients (AEC) show that aerosols were concentrated within the boundary layer (below 2 km) in Pune and Delhi, with the highest AEC values observed up to 500 meters. Compared to urban locations, the AEC values over Mahabaleshwar are much smaller; however, the average AEC profile suggests that the air in Mahabaleshwar is homogenous through the boundary layer. MAX-DOAS was also effective at observing high aerosol events, which compared well with ground-based samplers. Overall, this study offers insights into the aerosol distribution and vertical profiles in various regions of India and demonstrates the usefulness of MAX-DOAS in aerosol characterization in India.