Ultrafine particle number concentration and its size distribution during Diwali festival in megacity Delhi, India: Are 'green crackers' safe?

Since the air pollution and noise generated from fireworks are related to air quality and human health, the regulatory bodies had implemented the eco-friendly "Green Crackers" in megacity Delhi, India, to celebrate Diwali 2019 with the permission of a specific time slot (8:00 p.m. to 10:00 p.m.). The present study was conducted on a residential educational institute campus to evaluate the particle number size distribution (PNSD) of green cracker emissions. During the Diwali event period, the high peak of particle number concentration (PNC) reached 1.7 × 105 # cm-3 with a geometric mean diameter (GMD) of ∼44 nm. The average PNC increment on Diwali day was 138% and 97% compared to pre (October 26, 2019) and post (October 28, 2019) Diwali period, respectively, including 468%, 142%, 65%, 75% on pre-Diwali and 485%, 110%, 32%, 26% on post- Diwali 2019 period in terms of Nucleation mode (10 nm < Dp < 20 nm), Small Aitken mode (20 nm < Dp < 50 nm), Large Aitken mode (50 nm < Dp < 100 nm), and Accumulation mode (100 nm < Dp < 1000 nm), respectively. Unlike traditional firework emissions, green crackers had a high UFP/Ntotal ratio of 0.72, including Nucleation mode-0.35, Aitken mode-0.30, and Accumulation mode 0.35, distinguishing it from other pre-and post-Diwali particle number size distribution-dN/dlogDp curves. These observations indicate that green crackers emit more particles with smaller diameters than traditional crackers. Recommendations for using green crackers for Diwali celebrations may be an option if lower size-diameter particle emission could be controlled by changing the material composition of the green crackers. More research studies need to be conducted to assess atmospheric emissions of green crackers and their health impacts to evaluate whether they are better or worse than traditional crackers.