Abstract
This paper discusses the influence of aerosols on UV erythemal dose over four metro cities in India. Tropospheric Emission Monitoring Internet Service (TEMIS), archived UV-index (UV-I), and UV daily erythemal dose obtained from SCIAMACHY satellite were used in this study during June 2004 and May 2005 periods covering four important Indian seasons. UV-Index (UV-I), an important parameter representing UV risk, was found to be in the high to extreme range in Chennai (8.1 to 15.33), moderate to extreme range in Mumbai and Kolkata (5 to 16.5), and low to extreme over Delhi (3 to 15). Average UV erythemal dose showed seasonal variation from 5.9 to 6.3 KJm−2during summer, 2.9 to 4.4 KJm−2during postmonsoon, 3 to 4.5 KJm−2during winter, and 5.1 to 6.19 KJm−2during premonsoon seasons over the four cities. To estimate the influence of aerosols on reducing UV dose, UV aerosol radiative forcing and forcing efficiency were estimated over the sites. The average aerosol forcing efficiency was found to be from-1.38±0.33to-3.01±0.28 KJm−2AOD−1on different seasons. The study suggests that aerosols can reduce the incoming UV radiation dose by 30–60% during different seasons.
Highlights
Ultraviolet radiation, in spite of its nominal presence in solar spectrum, is important in human health perspectives
UV erythemal (UVE) dose and UV-I were found to be high during June over all the four sites
The minimum values of UV-I and UVE were observed during December-January
Summary
Ultraviolet radiation, in spite of its nominal presence in solar spectrum, is important in human health perspectives. The UV region of the spectrum mainly consists of UV-C (200– 280 nm), UV-B (280–315 nm), and UV-A (315–400 nm) Out of these UV-B is the most important spectral range, as it directly influences the human health. The UV radiation reaching the earth surface is modulated by the ozone concentration, cloud cover, solar zenith angle, and aerosols. Several studies report the influence of cloud cover on UV radiation. A few studies reported the variation of UV radiation and UV-index over Indian region [10, 11]. Most of the studies ignore the aerosol component and its influence on UV radiative transfer. Reference [12] has suggested that aerosol vertical (height) distribution can affect surface UV irradiances by 2–5% for optical depth observations at visible wavelengths.
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