Physico-Chemical Properties and Deposition Potential of PM2.5 during Severe Smog Event in Delhi, India

Abstract

The present work studies a severe smog event that occurred in Delhi (India) in 2017, targeting the characterization of PM_2.5 and its deposition potential in human respiratory tract of different population groups in which the PM_2.5 levels raised from 124.0 µg/m³ (pre-smog period) to 717.2 µg/m³ (during smog period). Higher concentration of elements such as C, N, O, Na, Mg, Al, Si, S, Fe, Cl, Ca, Ti, Cr, Pb, Fe, K, Cu, Cl, P, and F were observed during the smog along with dominant organic functional groups (aldehyde, ketones, alkyl halides (R-F; R-Br; R-Cl), ether, etc.), which supported potential contribution from transboundary biomass-burning activities along with local pollution sources and favorable meteorological conditions. The morphology of individual particles were found mostly as non-spherical, including carbon fractals, aggregates, sharp-edged, rod-shaped, and flaky structures. A multiple path particle dosimetry (MPPD) model showed significant deposition potential of PM_2.5 in terms of deposition fraction, mass rate, and mass flux during smog conditions in all age groups. The highest PM_2.5 deposition fraction and mass rate were found for the head region followed by the alveolar region of the human respiratory tract. The highest mass flux was reported for 21-month-old (4.7 × 10² µg/min/m²), followed by 3-month-old (49.2 µg/min/m²) children, whereas it was lowest for 21-year-old adults (6.8 µg/min/m²), indicating babies and children were more vulnerable to PM_2.5 pollution than adults during smog. Deposition doses of toxic elements such as Cr, Fe, Zn, Pb, Cu, Mn, and Ni were also found to be higher (up to 1 × 10^-7 µg/kg/day) for children than adults.