Source Identification of Indoor Particulate Matter and Health Risk Assessment in School Children

A large number of children have been regularly exposed to elevated levels of vehicular emissions because of the proximity of urban schools to motorways. In this study, particulate matter (PM) concentrations were monitored in a naturally ventilated classroom located near an urban road in Chennai, India. The 24-h average suspended particulate matter (SPM), ${\mathrm{PM}}_{10}$, ${\mathrm{PM}}_{2.5}$, and ${\mathrm{PM}}_1$ concentrations in the classroom were found to be 168.64, 135.88, 42.95, and $25.89\mathrm{\mu g}/{\mathrm{m}}^3$, respectively. Chemical characterization of SPM samples indicated the dominance of organic carbon ($19.3\mathrm{\mu g}/{\mathrm{m}}^3$), ${\mathrm{SO}}_4^{2-}$ ($10.3\mathrm{\mu g}/{\mathrm{m}}^3$), elemental carbon ($6.3\mathrm{\mu g}/{\mathrm{m}}^3$), ${\mathrm{NO}}_3^{-}$ ($5.7\mathrm{\mu g}/{\mathrm{m}}^3$), ${\mathrm{NH}}_4^{+}$ ($5.6\mathrm{\mu g}/{\mathrm{m}}^3$), ${\mathrm{Na}}^{+}$ ($4.2\mathrm{\mu g}/{\mathrm{m}}^3$), ${\mathrm{Cl}}^{-}$ ($3.6\mathrm{\mu g}/{\mathrm{m}}^3$), and Ca ($3.4\mathrm{\mu g}/{\mathrm{m}}^3$) concentrations. Source apportionment of indoor SPM using the chemical mass balance model showed that soil dust (31%) was the major contributor followed by diesel exhaust (24%), secondary ammonium sulfate (13%), secondary ammonium nitrate (11%), chalk dust (7%), marine aerosols (7%), paved road dust (6%), and gasoline exhaust (1%). Health risk assessment indicated that the total hazard quotient of elements was higher than the recommended value. The total excess cancer risk was found to be four times higher than the acceptable value.