The air quality in the national capital has turned poor on Sunday morning and expected to deteriorate further due to meteorological condition and an increase in stubble burning.
Concerned over deteriorating air quality, the Centre’s air quality panel on October 29, had directed authorities to impose a ban on construction and demolition activities in Delhi-NCR and other steps under stage III of the Graded Response Action Plan (GRAP).
SAFAR, a forecasting agency under the Union Ministry of Earth Sciences, said that the share of stubble burning in Delhi’s pollution rose to 21% on Saturday, the highest this year so far. It may increase up to 40% on Sunday and push the air quality into the severe zone.
Delhi Environment Minister Gopal Rai will chair a high-level meeting on Sunday to discuss measures to be implemented under stage III of GRAP. GRAP is a set of anti-air pollution measures followed in the capital and its vicinity according to the severity of the situation.
Air Quality Index is a tool for effective communication of air quality status to people in terms, which are easy to understand. It transforms complex air quality data of various pollutants into a single number (index value), nomenclature and colour.
There are six AQI categories, namely Good + Satisfactory, Moderately polluted, Poor, Very Poor, and Severe. Each of these categories is decided based on ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints). AQ sub-index and health breakpoints are evolved for eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short-term (up to 24-hours) National Ambient Air Quality Standards are prescribed.
Based on the measured ambient concentrations of a pollutant, sub-index is calculated,
which is a linear function of concentration (e.g. the sub-index for PM2.5 will be 51 at concentration 31 µg/m3, 100 at concentration 60 µg/m3, and 75 at concentration of 45
µg/m3). The worst sub-index determines the overall AQI. AQI categories and health breakpoints for the eight pollutants are as follow:
| AQI Category(Range) | PM10 24 – hr (µg/m3) | PM2.5 24 – hr (µg/m3) | NO2 24 – hr (ppb) | O3 8 – hr (ppb) | CO 8 – hr (ppm) | |||||||
| I low | I high | C low | C high | C low | C high | C low | C high | C low | C high | C low | C high | |
| Good | 0 | 50 | 0 | 50 | 0 | 30 | 0 | 21 | 0 | 25 | 0.0 | 0.9 |
| Satisfactory | 50 | 100 | 50 | 100 | 30 | 60 | 22 | 43 | 26 | 51 | 1.0 | 1.7 |
| Moderate | 100 | 200 | 100 | 250 | 60 | 90 | 44 | 96 | 52 | 86 | 1.8 | 8.7 |
| Poor | 200 | 300 | 250 | 350 | 90 | 120 | 97 | 149 | 87 | 106 | 8.8 | 14.8 |
| Very Poor | 300 | 400 | 350 | 430 | 120 | 250 | 150 | 213 | 107 | 381 | 14.9 | 29.7 |
| Severe | 400 | 500 | 430 | 700 | 250 | 380 | 214 | 750 | 382 | 450 | 29.8 | 40 |