Mangattayil Devaprasad

The burden of human health in urban clusters across India is associated with increasing fine particulate matter, PM2.5. However, associating PM2.5 health impacts with its mass burden alone without quantifiable relation to toxicity indicators over polluted regions may cause inaccurate estimations of disease burden resulting from varying chemical composition. Here, we present 17-day measurement results of oxidative potential quantified using hydroxyl radical assay (OP–OH) and environmentally persistent free radicals (EPFRs) in the coastal city of Chennai. We quantify EPFR concentration and OP–OH activity to be 34 ± 21 pmol m–3 and 11 ± 5.4 pmol min–1 m–3, respectively, and observed a weak association between OP–OH and EPFRs. Westerly and mixed wind separation helped characterize the distinct physical and chemical properties of PM2.5. During westerly winds, EPFRs were moderately correlated with particle number concentration 0.68; hydrocarbon-like organic aerosols (HOA), NO2, Fe, Sn, and Ti). During mixed winds, OP–OH exhibited moderate correlations with transition metals (Cr and Zn; R2 > 0.34) and particle number concentration >100 nm (R2 = 0.5) and a clear correlation with EPFRs (R2 = 0.59). Our result underscores the complexity of EPFRs and OP–OH in PM2.5 over polluted urban clusters, suggesting the importance of particle size dependence along with chemistry.

Chemically resolved gas- and particle-phase measurements capable of constraining new particle formation (NPF) remain scarce in South Asia. Here, we investigate the precursors driving NPF in a coastal megacity and examine why only a subset of nucleation events evolves into sustained particle growth. We present the first comprehensive 20-day field study in a Bay of Bengal coastal megacity, integrating aerosol microphysical, chemical, gas-phase, and VOC measurements with positive matrix factorization (PMF). Photochemically driven formation of 10–30 nm particles occurred between 07:00 and 11:00 IST, whereas sustained growth into the accumulation mode occurred only 2 of 20 days, with growth rates of 4.53 and 3.43 nm h⁻¹. The particle formation rate, condensation sink (CS), and coagulation sink did not differ between growth and non-growth days, indicating that neither formation intensity nor scavenging distinguished the two regimes. Instead, sustained growth occurred when northerly continental air masses prevailed, whereas growth ceased when a strong sea breeze shifted transport to marine air influenced by power-plant emissions. PMF resolved six factors, including an NPF factor dominated by 10–30 nm particles that was associated with biogenic VOCs. Its invariance between weekdays and weekends, and negative correlation with vehicular traffic factor, indicates that NPF was driven primarily by photo-oxidation of biogenic precursors, rather than by anthropogenic activity. These findings suggest that, in coastal cities, precursor availability and air-mass origin may exert a stronger influence on particle growth than CS, although long-term observations are needed to establish its broader applicability.

Chemically resolved gas- and particle-phase measurements capable of constraining new particle formation (NPF) remain scarce in South Asia. Here, we investigate the precursors driving NPF in a coastal megacity and examine why only a subset of nucleation events evolves into sustained particle growth. We present the first comprehensive 20-day field study in a Bay of Bengal coastal megacity, integrating aerosol microphysical, chemical, gas-phase, and VOC measurements with positive matrix factorization (PMF). Photochemically driven formation of 10–30 nm particles occurred between 07:00 and 11:00 IST, whereas sustained growth into the accumulation mode occurred only 2 of 20 days, with growth rates of 4.53 and 3.43 nm h⁻¹. The particle formation rate, condensation sink (CS), and coagulation sink did not differ between growth and non-growth days, indicating that neither formation intensity nor scavenging distinguished the two regimes. Instead, sustained growth occurred when northerly continental air masses prevailed, whereas growth ceased when a strong sea breeze shifted transport to marine air influenced by power-plant emissions. PMF resolved six factors, including an NPF factor dominated by 10–30 nm particles that was associated with biogenic VOCs. Its invariance between weekdays and weekends, and negative correlation with vehicular traffic factor, indicates that NPF was driven primarily by photo-oxidation of biogenic precursors, rather than by anthropogenic activity. These findings suggest that, in coastal cities, precursor availability and air-mass origin may exert a stronger influence on particle growth than CS, although long-term observations are needed to establish its broader applicability.

Chemically resolved gas- and particle-phase measurements capable of constraining new particle formation (NPF) remain scarce in South Asia. Here, we investigate the precursors driving NPF in a coastal megacity and examine why only a subset of nucleation events evolves into sustained particle growth. We present the first comprehensive 20-day field study in a Bay of Bengal coastal megacity, integrating aerosol microphysical, chemical, gas-phase, and VOC measurements with positive matrix factorization (PMF). Photochemically driven formation of 10–30 nm particles occurred between 07:00 and 11:00 IST, whereas sustained growth into the accumulation mode occurred only 2 of 20 days, with growth rates of 4.53 and 3.43 nm h⁻¹. The particle formation rate, condensation sink (CS), and coagulation sink did not differ between growth and non-growth days, indicating that neither formation intensity nor scavenging distinguished the two regimes. Instead, sustained growth occurred when northerly continental air masses prevailed, whereas growth ceased when a strong sea breeze shifted transport to marine air influenced by power-plant emissions. PMF resolved six factors, including an NPF factor dominated by 10–30 nm particles that was associated with biogenic VOCs. Its invariance between weekdays and weekends, and negative correlation with vehicular traffic factor, indicates that NPF was driven primarily by photo-oxidation of biogenic precursors, rather than by anthropogenic activity. These findings suggest that, in coastal cities, precursor availability and air-mass origin may exert a stronger influence on particle growth than CS, although long-term observations are needed to establish its broader applicability.

Chemically resolved gas- and particle-phase measurements capable of constraining new particle formation (NPF) remain scarce in South Asia. Here, we investigate the precursors driving NPF in a coastal megacity and examine why only a subset of nucleation events evolves into sustained particle growth. We present the first comprehensive 20-day field study in a Bay of Bengal coastal megacity, integrating aerosol microphysical, chemical, gas-phase, and VOC measurements with positive matrix factorization (PMF). Photochemically driven formation of 10–30 nm particles occurred between 07:00 and 11:00 IST, whereas sustained growth into the accumulation mode occurred only 2 of 20 days, with growth rates of 4.53 and 3.43 nm h⁻¹. The particle formation rate, condensation sink (CS), and coagulation sink did not differ between growth and non-growth days, indicating that neither formation intensity nor scavenging distinguished the two regimes. Instead, sustained growth occurred when northerly continental air masses prevailed, whereas growth ceased when a strong sea breeze shifted transport to marine air influenced by power-plant emissions. PMF resolved six factors, including an NPF factor dominated by 10–30 nm particles that was associated with biogenic VOCs. Its invariance between weekdays and weekends, and negative correlation with vehicular traffic factor, indicates that NPF was driven primarily by photo-oxidation of biogenic precursors, rather than by anthropogenic activity. These findings suggest that, in coastal cities, precursor availability and air-mass origin may exert a stronger influence on particle growth than CS, although long-term observations are needed to establish its broader applicability.