Water-soluble ions and carbon content of size-segregated aerosols in New Delhi, India: direct and indirect influences of firework displays.

The particle size distribution and water-soluble inorganic ion (WSII) and carbonaceous species in size-segregated aerosols, Dp < 0.95, 0.95 < Dp < 1.5, 1.5 < Dp < 3.0, 3.0 < Dp < 7.2, and 7.2 < Dp < 10 μm, were investigated during Diwali firework displays in New Delhi, India. The firework activity had the maximum contribution to the mass loading of PM0.95 (786 μg/m3) followed by PM0.95-1.5 (216 μg/m3) with all other three fractions accounting to a total of 214 μg/m3. The percentage contributions of WSII to the total mass of aerosols were highest in first two size fractions (39 and 40 %, respectively), compared to other fractions. The firework marker ion (Mg2+, Cl-, and K+) mass concentration shows higher values in PM0.95 during Diwali compared to before Diwali period. The mass size distribution of particles, NH4+, K+, Cl-, SO42-, Mg2+, and NO3-, also showed changes on the Diwali night compared to previous and after days. The high Cl-/Na+ (5.6) and OC/EC (3.4) ratio of PM0.95 can be used as the indicators of firework displays. The lowering of mixing height on Diwali night to 50 m compared to before (277 mts) and after (269 mts) Diwali period further concentrated the aerosols in ambient atmosphere. Therefore, the firework display not only released the gaseous or elemental constituent but also influenced the temperature profile and both put together result in high aerosol concentrations, WSII, OC, and BC contents in ambient atmosphere. The alveolar, respirable, and inhalable fractions accounted for 64.6, 90.8, and 97.8 %, respectively, of the total PM10 mass. People stay exposed to such high pollution level in short span of 6-8 h and experience adverse health impacts due to high mass concentrations and the chemical components of fine aerosols.