Delhi air improves to 'moderate' but the forecast stays 'poor'

Delhi's air improved on Monday, but the relief may not last. The air quality index (AQI) stood at 164 at 7am local time, according to the Central Pollution Control Board (CPCB). That is the 'moderate' band (101-200), better than Saturday's 191, but five stations were still 'poor' and the official forecast expects the AQI to return to that range between 26 and 28 October.

What happened

The CPCB calculates the AQI from several pollutants; PM2.5 was the lead pollutant at 30 of the 55 reporting stations. Jahangirpuri recorded the highest reading, 246, followed by Vivek Vihar (235) and CRRI Mathura Road (231). The wider capital region reached 168 on Sunday and white foam reappeared on the Yamuna, according to The Times of India.

On 21 October, the Commission for Air Quality Management (CAQM) invoked Stage 1 of the Graded Response Action Plan (GRAP) after the daily average AQI reached 245, according to the Indian government. It bans coal and firewood in tandoor ovens, restricts diesel generators, requires dust controls at construction sites and allows visibly polluting vehicles to be impounded.

On Sunday, Delhi's environment minister, Manjinder Singh Sirsa, met police commanders to coordinate winter measures, according to Hindustan Times. The problem recurs every year: weaker winds and lower temperatures hamper dispersion, and stubble burning and fireworks add to it, The Hindu notes.

The map: chronic exposure, not a daily episode

The map colours 195 countries and territories by the annual average exposure of their populations to PM2.5, measured in micrograms per cubic metre (µg/m³). The data are for 2023 and come from the World Bank, drawing on the WHO Global Health Observatory.

India records 54.1 µg/m³, more than ten times the WHO's annual guideline of 5 µg/m³. It is not an exception: Bangladesh reaches 69.3, Pakistan 58.4 and Nepal 53.2; Finland falls to 4.6 and the highest value is Qatar's 107.8. The map places India among the world's most exposed regions, but it does not explain this episode: it measures an annual national average, whereas the AQI is a daily index shaped by traffic, construction, stubble burning and wind.

What comes next

The early warning system expects a 'poor' AQI from 26 to 28 October and 'poor' or 'moderate' afterwards, according to its bulletin of 25 October. The mixing height will fall from 2,200 to 1,300 metres and the ventilation index from 11,000 to 3,800 m²/s; below 6,000 with winds under 10 km/h, dispersion is unfavourable.

Stage 1 of the GRAP applies when the AQI is 'poor'; the framework provides for further restrictions if it enters the 'very poor' band (301-400).