Fog-induced variations in aerosol optical and physical properties over the Indo-Gangetic Basin and impact to aerosol radiative forcing

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.

Quantitative assessment of AOD from 17 CMIP5 models based on satellite-derived AOD over India

“…Highest pollution levels are usually noted along the IndoGangetic Basin (IGB), which is also a region of high population density. This region is affected by dust storms during pre-monsoon season (Dey et al, 2004), and dense fog during winter Tare et al, 2006;Das et al, 2008). North-east India is a mountainous region of the Himalayas and receives the highest amount of rainfall in the country.…”

Characteristics of aerosols over Hyderabad in southern Peninsular India: synergy in the classification techniques

“…9a), the 72 % of the air masses arrive from northern directions, where intense fog and pollution-haze conditions occur during this season (Gautam et al, 2007;Das et al, 2008). The lower altitude trajectories favor the transport of pollution aerosols over Hyderabad in winter.…”

Contrasting aerosol characteristics and radiative forcing over Hyderabad, India due to seasonal mesoscale and synoptic‐scale processes

“…During winter, 93% of the air masses originate from northern directions, originating mainly from the Indo-Gangetic Plains (IGP), where intense fog and pollution-haze conditions occur (e.g. Das et al, 2008). The lower altitude trajectories favour the transport of pollution aerosols over Hyderabad during winter; thus the relatively high AODs compared with those from other polluted urban locations (e.g.…”