Abstract
Abstract. A detailed study on the changes in aerosol physical and optical properties during fog events were made in December 2004 at Hissar (29.13° N, 75.70° E), a city located in the Indo-Gangetic basin. The visible aerosol optical depth was relatively low (0.3) during the initial days, which, however, increased (0.86) as the month progressed. The increasing aerosol amount, the decreasing surface temperature and a higher relative humidity condition were found favoring the formation of fog. The fog event is also found to alter the aerosol size distribution. An increase in the number concentration of the nucleation mode (radius<0.1 μm) particles, along with a decrease in the mode radius showed the formation of freshly nucleated aerosols. In the case of accumulation mode (0.1 μm<radius<1.0 μm) an increase in the mode radius was observed showing the hygroscopic and coagulation growth of particles. The observed aerosol optical depth spectra are model fitted to infer the aerosol components which are further used to compute the aerosol radiative forcing. The top of the atmosphere forcing is found to increase during foggy days due to large backscattering of radiation back to space. It is also shown that during foggy days, as the day progresses the RH value decreases, which reduces the forcing value while the increasing solar elevation increases the forcing value. Thus the fog event which prolongs longer into the daytime has a stronger effect on the diurnally averaged aerosol radiative forcing than those events which are confined only to the early morning hours.
Highlights
Aerosols play an important role in the Earth’s atmosphere system by interacting with the incoming solar radiation and the outgoing longwave radiation
In this paper we study the aerosol properties and their changes during fog conditions in the Indo-Gangetic Basin (IGB) through a month long field campaign conducted at Hissar (29.13◦ N, 75.70◦ E) (Fig. 1) in December 2004 as part of the ISRO-GBP Land Campaign-II
Under the ISRO-GBP land campaign II a detailed study on the aerosol physical and optical properties was made during December 2004 at Hissar, a city located in the Indo-Gangetic basin
Summary
Aerosols play an important role in the Earth’s atmosphere system by interacting with the incoming solar radiation and the outgoing longwave radiation. Within the Indian region, the Indo-Gangetic Basin (IGB), located in the northern part of India, is of particular importance as it is the highly aerosol loaded region and has the largest aerosol optical depth during both summer and winter seasons (Jethva et al, 2005). In this region the domestic energy consumption largely depends on biofuels (such as cow-dung cake, wood, straw and other agriculture wastes) in rural areas and mainly fossil fuels in urban areas. We estimate the aerosol radiative forcing and its diurnal variation during the fog period and compare with that during clear sky conditions
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