Influence of regional and long range transport air masses on fog water composition, contribution and toxicological response at Indo Gangetic Plain

Abstract

Indo Gangetic Plain (IGP) is considered to be one of the hotspots for the occurrence of fog events during the winter time. However, the studies on fog water characteristics reported for IGP are limited and toxicological analysis have not been reported still which indirectly affects air quality. Towards this, we chose a rural site at northern edge of IGP and collected fog water samples during winter sampling campaign for the year 2017–18. Twenty-eight fog water samples were collected during the night time and analyzed for pH, conductivity, inorganic species, dissolved organic carbon (DOC), metals and toxicological evidence based on nuclear factor kappa-light-chain-enhancer of activated B cells (NF-KB) activity. Nitrate and sulfate were dominant anionic species but excess ammonium and calcium neutralized the fog water such that pH value averaged around 6.7 ± 0.2. Surprisingly, the concentration of DOC (200 ± 80 mg/l) was found to be comparable with the total inorganic ions (188 ± 62 mg/l). The concentration of DOC was found to have an inverse relationship with liquid water content influencing dilution effect whereas inorganic ions concentrations did not show any significant relation. The observed and predicted sulfate concentration in fog water highlighted the sulfate is contributed significantly by aqueous processing of gaseous SO2 into fog water droplets. Cluster analysis results for backward air mass trajectory showed that the contribution of inorganic species including nitrate and sulfate was significantly higher for long range associated air masses whereas regional air masses had significant DOC contribution. All the fog water samples showed pro inflammation response based on NF-Kβ activity values and which was further found to be 52% higher for the local emissions compared to long range transport emissions. Thus this study showed the influence of local and long range transport air mass on fog water chemical and toxicological characteristics.