Solar eclipse-induced variations in solar flux, j(NO2) and surface ozone at Kannur, India

Abstract

Surface ozone is mainly produced by the photodissociation of nitrogen dioxide (NO2) by solar UV radiation. Subsequently, solar eclipses provide one of the unique occasions to explore the variations in the photolysis rate of NO2 and their significant impact on the production of ozone at a location. This study aims to examine the diurnal variations in the photodissociation rate coefficient of NO2, (j(NO2*)), and mixing ratios of surface ozone and NO X * (NO + NO2*) during the solar eclipse that occurred on 15 January 2010 at Kannur (11.9°N, 75.4°E, 5 m amsl), a tropical coastal site on the Arabian Sea in South India. This investigation was carried out on the basis of the ground level observations of surface ozone and its prominent precursor NO2*. The j(NO2*) values were estimated from the observed solar UV-A flux data. A sharp decline in j(NO2*) and surface ozone was observed during the eclipse phase because of the decreased efficiency of the ozone formation from NO2. The NO2* levels were found to increase during this episode, whereas the NO levels remained unchanged. The surface ozone concentration was reduced by 57.5%, whereas, on the other hand, that of NO X * increased by 62.5% during the solar eclipse. Subsequently a reduction of *% in the magnitude of j(NO2*) was found here during the maximum obscuration. Reductions in solar insolation, air temperature and wind speed were also observed during the solar eclipse event. The relative humidity showed a 6.4% decrease during the eclipse phase, which was a unique observation at this site.