UV Erythemal Radiation and Its Sensitivity to Changes in Total Column Ozone and Aerosols

Ultraviolet erythemal radiation (UVER) measurements made at the Nowrosjee Wadia College (NWC) campus, Pune (India) were analysed to investigate temporal variability of UVER, to quantify effects of total column ozone (TCO) and aerosols on surface reaching UVER and to inter-compare ground-based and satellite retrieved UVER data. Diurnal variability in UVER exhibits a significant change with respect to local noon time followed by a month-to-month cyclical trend. The rate of ascent/descent of UVER during morning/evening time in winter is seen to be 0.43 minimum erythemal dose per hour (MED/hr) while during pre-monsoon season it is 0.63 MED/hr. Overall, the average value of the UVER for study period comes out to be 2.93 ± 0.8 MED/hr which is ~ 1.5 times higher than the threshold limit at which the Indian skin gets affected. There exists a quasi-anti-phase relationship between UVER and aerosol/TCO data pairs highlighting their influence on surface reaching UVER. Analysis reveals an inverse relationship between UV index (UV-I) (hence UVER) and aerosol index (AI) yielding Pearson correlation coefficient (r) in the range − 0.21 to − 0.88 for the period 2012–2013 and 2014–2015. The study further elucidates that the observed overall rate of decrement in UVER as a function of TCO is found to be 2.8 ± 1.5%. The Ozone Monitoring Instrument (OMI) retrieved UVER overestimates the UV-Biometer measured UVER by about 30%. The reason for overestimations being the non-inclusion of absorbing aerosols in the UVER retrieval algorithm employed in OMI estimations as well as prevalent atmospheric conditions.