Chemical speciation and source apportionment of ambient PM2.5 in New Delhi before, during, and after the Diwali fireworks

TL;DR

This study quantifies the dramatic increase in PM2.5 pollution during Diwali fireworks in New Delhi, identifies key sources and tracers, and distinguishes the primary impact of biomass burning from fireworks on post-Diwali air quality.

Contribution

It provides detailed chemical speciation and source apportionment of PM2.5 during Diwali, highlighting the dominant role of fireworks and biomass burning in pollution levels.

Findings

PM2.5 increased up to 16 times during Diwali

Fireworks contributed 95% of elemental PM2.5 during Diwali

Biomass burning emissions drive post-Diwali haze events

Abstract

Diwali is among the most important Indian festivals, and elaborate firework displays mark the evening's festivities. This study assesses the impact of Diwali on the concentration, composition, and sources of ambient PM2.5. We observed the total PM2.5 concentrations to rise to 16 times the pre-firework levels, while each of the elemental, organic, and black carbon fractions of ambient PM2.5 increased by a factor of 46.1, 3.7, and 5.6, respectively. The concentration of species like K, Al, Sr, Ba, S, and Bi displayed distinct peaks during the firework event and were identified as tracers. The average concentrations of potential carcinogens, like As, exceeded US EPA screening levels for industrial air by a factor of ~9.6, while peak levels reached up to 16.1 times the screening levels. The source apportionment study, undertaken using positive matrix factorization, revealed the fireworks to account for 95% of the total elemental PM2.5 during Diwali. The resolved primary organic emissions, too, were enhanced by a factor of 8 during Diwali. Delhi has encountered serious haze events following Diwali in recent years; this study highlights that biomass burning emissions rather than the fireworks drive the poor air quality in the days following Diwali.