Bihar's Begusarai emerged as the world's most polluted metropolitan area while Delhi was identified as the capital city with the poorest air quality, according to this report by the Swiss organisation IQAir.

The 2023 World Air Quality Report provides a global review of air quality data for the year 2023. The report summarizes PM2.5 air quality data from 7,812 cities spanning 134 countries, regions, and territories. The data utilized to create this report was aggregated from more than 30,000 air quality monitoring stations operated by research institutions, governmental bodies, universities and educational facilities, non-profit organizations, private companies, and citizen scientists. PM2.5 data is reported in units of micrograms per cubic meter (μg/m3) and incorporates the latest World Health Organization (WHO) annual PM2.5 guideline and interim targets for data visualization and risk communication (released in 2021). The 2023 World Air Quality Report was created from real-time air quality data sourced from IQAir’s global air quality monitoring platform that vets incoming data with validation and calibration protocols to harmonize air quality data from monitoring stations around the world. [2]