Assessment of satellite-retrieved surface UVA and UVB radiation by comparison with ground-measurements and trends over Mega-city Delhi. (September 2018)

• Record Type: Journal Article
• Authors: Singh, Sachchidanand; Lodhi, Neelesh K.; Mishra, Amit Kumar; Jose, Sandhya; Kumar, S. Naresh; Kotnala, R.K.
• Is Part Of: Atmospheric environment. Volume 188(2018)
• Page Start: 60
• Page End: 70
• Publication Date: 2018-09
• Subjects: UVA -- UVB -- CERES -- AOD -- Radiometer; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2018.06.027
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Solar UV radiation reaching the Earth's surface is known to have various effects on human health and on the ecosystem. Ground-based measurements of surface UV radiation are spatially sparse and in many cases do not provide long time series. Higher spatial coverage can be provided by measurements from satellite based instruments, but these measurements need to be compared to ground-based measurements of sufficient quality before they can be used in health and ecosystem applications. Here, we compare the measurements of surface solar UV radiation in UVA (315–400 nm) and UVB (280–315 nm) bands with the satellite retrievals (CERES) and validate the latter at an urban location, Delhi, India. We have also used MODIS-retrieved aerosol optical depth (AOD) and cloud optical depth (COD) data to see the effect of atmospheric opacity on UV radiation. Ground-based measurements of UVA and UVB were performed from 01 October, 2012 to 30 September, 2015. Correlations between daily surface measurements and CERES-derived surface UV fluxes showed very good agreement (r ∼ 0.92–0.93) over Delhi. We found a negative correlation between UV fluxes and AOD over Delhi during all seasons. A unit increase in AOD leads to a decrease of ∼4–5 Wm -2 in UVA and ∼0.09–0.14 Wm -2 in UVB over Delhi. The trend analysis from monthly mean CERES-derived UV fluxes for 17 years data reveals that UVA and UVB are decreasing ∼0.07 Wm -2 yr −1 and 0.003 Wm -2 yr −1, respectively with AOD increase (∼0.005 yr −1 ) over Delhi. The simultaneous increase in aerosol loading with decrease in UV fluxes at the surface may be explained as a masking effect of ever increasing pollution on surface UV radiation over Delhi. Our results show ∼10% and ∼20% decrease (with respect to mean) in UVA and UVB surface fluxes, respectively during last 17 years. Highlights: CERES derived UV-A and UV-B compared with surface measurements at Delhi. Statistical analysis showed good agreement between CERES & ground measurements. Surface UVA & UVB flux had a negative correlation with aerosol loading. 4–5 Wm -2 decrease in UVA and 0.09–0.14 Wm -2 in UVB per unit increase in AOD. 10–20% decrease in UVA & UVB surface fluxes seen during last 17 years at Delhi.