Influence of aerosol composition on visibility in megacity Delhi

Influence of aerosol composition on visibility degradation in megacity Delhi has been quantified using model-derived seasonal mean aerosol composition constrained by satellite-measured columnar aerosol optical depth spectrum. Aerosols contribute ∼90% to the observed visibility degradation in non-foggy condition, while its relative contribution decreases rapidly at RH ≥ 80% due to stronger relative influence of fog droplets on attenuation of radiation, especially during the winter season. Visibility is most sensitive to water-soluble particles and soot in all seasons. Sensitivity study shows that visibility does not respond strongly to reduction of mass concentration of insoluble, accumulation mode and coarse mode dust particles. Reduction of mass concentration of soot and water-soluble particles in the range of 10%–50% will lead to an increase in visibility by 2.4 ± 0.1%–11.3 ± 1.6% and 4.9 ± 2%–29 ± 12% respectively. Reduction of the last two anthropogenic components has co-benefits, as it may reduce fog formation and thus further enhance the visibility along with an improved air quality in terms of associated health and climatic effects.