Delhi and Noida recorded very poor air quality on Monday morning, according to readings reported from the Central Pollution Control Board's Sameer application. Delhi's Air Quality Index stood at 310 and Noida's at 311 at 8:05 a.m. on November 2, the Indian Express reported.
The figures describe a particular morning observation. They are not a final daily average, and they should not be presented as a live reading throughout the day. Air-quality values can change as monitoring data and weather conditions change.
Different cities, different readings
The same report placed Ghaziabad at 278 and Gurugram at 230, both in the poor category, while Faridabad recorded 116, in the moderate category. The variation shows why a single figure should not be applied to the whole National Capital Region.
Even within a city, individual monitoring stations can record different pollution levels. A station reading, a city summary and a daily bulletin answer different questions. Comparisons become misleading when their locations, averaging periods or observation times are omitted.
Business Standard reported Delhi's index at 307 at 7 a.m., earlier than the 310 reading. The difference between those two observations does not by itself indicate that one report is wrong. They refer to different moments during the morning.
What very poor means
India's national AQI framework places readings from 301 to 400 in the very poor category. The index is designed to communicate air conditions in a form that is easier to understand than a list of separate pollutant concentrations.
It is not a direct count of particles in a person's lungs, nor does it measure an individual's exposure. Exposure depends on where someone spends time and the conditions they encounter. The CPCB framework associates very poor air with the risk of respiratory illness on prolonged exposure.
The framework also distinguishes poor, moderate and severe conditions. Those labels should not be substituted for one another for emphasis. A reading of 310 is very poor under the Indian system; calling it severe would change the official classification.
Pollution measures and the morning deterioration
The worsening morning readings followed the introduction of expanded winter pollution-control measures on November 1, according to Business Standard. Their arrival has not prevented the city from recording another period of unhealthy air.
One morning's index cannot, however, establish the effectiveness of every measure. Assessing that requires a longer record and attention to emissions, atmospheric conditions and enforcement. The available observations do not identify a precise contribution from traffic, construction, industry or agricultural fires.
