Black carbon and chemical characteristics of PM₁₀ and PM₂.₅ at an urban site of North India

The concentrations of PM₁₀, PM₂.₅ and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM₁₀ and PM₂.₅ concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) µgm⁻³ respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM₂.₅/PM₁₀ varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM₁₀ and PM₂.₅, is deemed as the contribution of the coarse fraction (PM₁₀−₂.₅). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 µgm⁻³, 13.07%), mineral matter (12.32 µgm⁻³, 10.06%) and salt particles (4.92 µgm⁻³, 4.02%). PM₂.₅ are mainly made up of undetermined fractions (39.46 µgm⁻³, 40.9%), secondary inorganic aerosols (26.15 µgm⁻³, 27.1%), salt aerosols (22.48 µgm⁻³, 23.3%) and mineral matter (8.41 µgm⁻³, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) µgm⁻³, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM₁₀ and PM₂.₅. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl⁻, SO ₄ ²⁻ , K⁺, Na⁺, Ca²⁺, NO ₃ ⁻ and Mg²⁺ with PM₂.₅ on one hand and Mg²⁺ with PM₁₀ on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi.