Was Delhi pollution data during Diwali misleading?

BBC Verify has found significant discrepancies between two Indian government datasets showing Delhi's air pollution during Diwali, indicating official figures may not have captured the full extent of the problem. As fireworks lit up Delhi's skies on 8 November to mark one of India's biggest festivals, some monitoring stations recorded very high levels of PM2.5, a fine particulate matter which can damage people's lungs and cause other serious health problems.

But every hourly PM2.5 reading above 1,000 micrograms per cubic metre was missing from the widely cited air quality index (AQI) published by the Central Pollution Control Board (CPCB), when compared to data from the Delhi Pollution Control Commission (DPCC). Delhi is one of the most polluted cities in the world and often has dangerously poor air quality , so it is vital people living in India's capital can trust the official data.

Firecrackers are not the only cause of pollution, which is also attributed to a mix of reasons including vehicle emissions, construction dust, farm fires and atmospheric factors.