The role of particulate matter in reduced visibility and anionic composition of winter fog: a case study for Amritsar city

Severe fog events during winter months in India are a serious concern due to the higher incidence of road accidents, flight delays and increased occurrence of respiratory diseases. The present paper is an attempt to study the twenty fog samples collected from the rooftop of an academic building of Guru Nanak Dev University, Amritsar, India from November 2017 to January 2018. Fog samples were analysed for various parameters viz. pH, electrical conductivity (EC), chloride (Cl(−)), nitrate (NO(3)(−)) and sulphate (SO(4)(2−)) levels. The pH, EC, and Cl(−), NO(3)(−) and SO(4)(2−) levels in the fog samples were estimated as 6.3–7.9, 240–790 μS cm(−1), 108–2025 μeq L(−1), 105–836 μeq L(−1) and 822–5642 μeq L(−1), respectively. It was noticed that sulphate was the dominant anion in fog samples. The SO(4)(2−) to NO(3)(−) molar ratio in the fog was estimated as 7.6 which suggests the burning of fossil fuel as the major pollutant from vehicular exhausts. Multiple regression analysis was performed to evaluate the effect of PM(2.5)/PM(10) ratio and relative humidity (RH) on visibility. A box-cox plot of power transformation produced better model fitting, employing a square root transformation of the visibility which indicated that the PM(2.5)/PM(10) and RH have an exponential effect on visibility.