Gaseous and particulate reactive nitrogen species in the indoor air of selected households in New Delhi.

The present study reports the indoor abundance of inorganic trace gases (NH, NO and SO) and their corresponding particulates (NH, NO and SO) along with other major ionic species present in the aerosol form (Cl, F, Na, K, Ca and Mg), in the urban households of megacity Delhi (India). Two different households (DH site and MH site) were selected in the city based on the variation in the land use patterns of the locations in which they were situated. Trace gases followed the order NH > SO > NO at both the sites with NH contributing about 90% and 85% to the total Nr species at DH and MH sites, respectively. NH showed maximum indoor concentrations during monsoon season whereas NO and SO were higher during winter season. The gas to particle conversion of the inorganic trace gases was studied by calculating their oxidation ratios which followed the order SOR > NOR > NHR, indicating that SO showed more oxidative conversion to SO as compared to NO and NH in the indoor setup. The chemical composition of the particulates revealed that Ca and SO were the most abundant cation and anion, respectively, among the measured ionic species at both sites and the concentrations of all the major ions were higher for the industrial MH site as compared to the residential DH site. Source apportionment using principal component analysis and mass ratios showed that indoor activities such as cooking, cleaning along with others such as biomass burning and dust resuspension were responsible for the indoor composition of particulates at DH site whereas outdoor influences such as coal burning and industrial emissions from local sources were prominent at MH site due to its industrialized surroundings. For naturally ventilated households (such as the present study), it was observed that the emissions generated indoors as well as the characteristic outdoor influences seem to influence the overall indoor air composition and quality.