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Indoor air pollution is a matter of serious concern in the mega cities which are grappling with poor air quality. There are very few reports available that discuss the indoor air quality of gaseous ammonia (NH3). This study reports the abundance and risk assessment of NH3 in two distinct urban households of Delhi city during July 2017 to June 2018. Results showed that the NH3 concentrations were consistently higher during entire sampling period at the Dwarka household (DH) site which represented the residential sector having an average value of 102.5 µg/m3, as compared to the Mayapuri household (MH) site which represented the industrial sector having an average value of 57.2 µg/m3. The spatio-temporal analysis suggested a characteristic seasonal influence as indoor concentrations were very high during monsoon season following the order, monsoon > summer > post-monsoon ≥ winter, at DH site but indoor NH3 at MH site did not show any remarkable seasonal variation except a sweeping increase during monsoons. Short term and long term health risk characterisation using multiple appropriate toxicological end limits for NH3 in the two households showed that at its present concentrations indoor NH3 cannot be a health hazard to the inmates. However, it does not fail to escape our notice that mushrooming urban areas with their complex problems such as poor sanitation, industrialisation, waste management, high vehicular traffic, high occupant density, etc. have become major hubs of continual rise in indoor ammonia.

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The dry deposition of PM on foliage of indoor plants in the households of Delhi has been reported in this study. It was observed that dustfall fluxes were higher at the industrial site (MH) as compared to the residential site (DH). Seasonal variations in dust deposition indicated that it was highest in the winter season and lowest in the monsoon season. Chemical profiling of the deposited dust marked that dust was less basic at MH as compared to DH and Ca 2+ was ubiquitously the most abundant cation at both sites whereas Cland SO4 2were the most abundant anions at DH and MH, respectively. Abundance of K + , NO3and NH4 + etc. indicated the influence of anthropogenic activities. The number of PM deposited on the foliar surfaces of indoor plants was also estimated and divided into PM1, PM2.5 and PM10 based on their size because particle count is more appropriate than particle mass for estimation of finer PM. PM accumulation on the foliar surfaces of selected plants for the present study followed the order, PM1 > PM2.5 > PM10 at both the sites.The foliar micromorphology of abaxial surfaces of the plants accounted for significant interspecies variability due to difference in presence of grooves and undulations, high stomatal density, epicuticular wax etc. Leaves with densely arranged grooves and ridges showed more PM accumulation. Investigation of plants with respect to dust deposition and selection of species which can perform the dual functions of improving air quality and providing aesthetic value are needed for understanding the role of vegetation in air pollution mitigation approaches in real life environment.