Was Delhi pollution data during Diwali misleading?
Summary
BBC Verify found that Delhi’s widely cited air pollution data omitted very high PM2.5 readings during Diwali on 8–9 November. The Central Pollution Control Board said its equipment is calibrated only up to 1,000 micrograms per cubic metre, so higher readings are excluded; this left its reported averages far below figures in a separate dataset.Key Facts
- Across the same 30 monitoring stations over 24 hours, available CPCB readings averaged 240 micrograms per cubic metre, compared with 551 in DPCC data.
- DPCC records contained 116 hourly readings above 1,000 micrograms per cubic metre that did not appear in the CPCB records.
- Three monitoring stations recorded hourly PM2.5 concentrations above 3,000 micrograms per cubic metre, according to DPCC data examined by BBC Verify.
- From 21:00 on 8 November to 07:00 on 9 November, 217 hourly PM2.5 observations were missing across 59 CPCB stations; only 16 stations reported complete data.
- CPCB methodology requires at least 16 hours of valid PM2.5 measurements for a station to calculate a daily average.
- At the RK Puram station, BBC Verify calculated a 24-hour average of about 945 micrograms using available hourly readings; CPCB data for 14 hours gave an average of 299.
- A researcher at the Centre for Research on Energy and Clean Air said excluding extreme readings risks misrepresenting pollution and weakening trust in official figures.
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