Delhi-NCR AQI: How monitor placement shapes daily readings

Delhi’s AQI was 324 on November 2, calculated from readings available at 58 of the 59 monitoring stations listed in the CPCB’s daily bulletin.

Those continuous stations, or CAAQMS, provide the day-long readings used for the daily AQI and for pollution-control measures under the Graded Response Action Plan. Manual stations work differently: they collect 24-hour samples twice a week.

CPCB’s 2019 framework sets a city’s minimum network by population, using the 2011 Census. A city with more than five million residents should have at least 16 stations, including 12 continuous monitors. Delhi’s stations are run mainly by the Delhi Pollution Control Committee, CPCB, the India Meteorological Department and the Indian Institute of Tropical Meteorology.

Location matters too. The guidelines call for monitors to sit 3-10 metres above ground, at least 20 metres from trees, and in sites open on three of four sides rather than hemmed in by walls or placed beside busy roads.

Elsewhere in NCR, CPCB’s bulletin lists eight stations in Ghaziabad, seven in Noida, four in Gurugram, and three each in Faridabad and Greater Noida. Residents can compare hourly readings station by station.