Indoor ultrafine particle concentrations and their size distributions during festival-associated emissions in urban region

Indoor air quality is crucial for the well-being of residents, as people spend 80 % of their time indoors. This study investigated the impact of festival activities on household indoor air quality in megacity Delhi. The study included different phases and activities during the festival and normal conditions and analyzed the impact of different emission sources. During the festival period, the indoor ultrafine particle concentration was found to be 6.7 × 10⁴ #cm⁻³, which was the highest observed indoor concentration throughout the study. The particle number concentration of the nanoparticles in indoor environment ranged from 10⁴ to 10⁵ #cm⁻³. Ultrafine size range particles contributed up to ∼85 % to the total particle numbers. Fireworks contributed to higher particle numbers in indoors, followed by cooking, dusting, and worshiping. The size distribution pattern of the particles emitted during cooking activities and fireworks was found to be different. Particle size range 10–30 nm contributed ∼31 % to total particle numbers on fireworks day, whereas on a normal day, it contributed only ∼13 %. During normal day, 100–1000 nm size particles contributed ∼50 % to total particle numbers. The diurnal pattern of the indoor environment was different from the outdoor. The outdoor fireworks activities also influenced indoor pollutants with respect to trace metals, which makes the indoor air quality more toxic, and affects the occupants' health.