Effect of Tropospheric Nitrogen Dioxide on Incoming Solar Radiation

Abstract

Incoming solar radiation is known to undergo an interaction with the constituents of the Earth’s atmosphere. This interaction is expressed by means of the mechanisms of absorption, scattering and reflection. The occurrence of each such mechanism depends on the size of the molecules in relation with the wavelength of the incoming radiation. The study of the interaction of solar radiation with atmospheric constituents, including aerosols, has long attracted scientific interest; such an interaction is related to climate-change issues. Among the atmospheric constituents, interest has been given to the anthropogenically-derived nitrogen dioxide (NO2) in the troposphere, since there has been found that anthropogenic aerosols have been playing an important role in their interaction with the incoming solar radiation. That is the reason for the recent discovery of the global dimming phenomenon. Mean daily solar radiation values from the Actinometric Station of the National Observatory of Athens (ASNOA) are compared with simultaneous ones of NO2 measured by the network of the Greek Ministry of Environment within the Athens basin. The period considered in this study covers the years 1990 – 2004. The study examines clear-sky conditions in order to show the influence of NO2 alone on solar radiation. The results show that increasing levels of NO2 cause smaller/greater scattering of solar radiation (global/diffuse components) at different rates, thus resulting in an attenuation of solar radiation; this attenuation rate is greater in the global component than in the diffuse one, in absolute terms.