Delhi pollution rises as wind speed falls

New Delhi: Pollution levels in Delhi rose on Sunday leading to a dip in air quality, with monitoring agencies forecasting a further spike over the next few days.

The Air Quality Index (AQI), calculated by the Central Pollution Control Board (CPCB), was 352 on a scale of 500. A score between 301 and 400 is considered “very poor” which can trigger respiratory illnesses on prolonged exposure.

Saturday’s AQI was 322. Scientists attributed the rise in pollution to a fall in wind speed and increased moisture in the air. The volume of particulate matter (PM), the dominant pollutant in Delhi’s air, rose through the day.

The readings of SAFAR, an agency under the Ministry of Earth Sciences, had PM2.5 at 194 and PM10 at 309 micrograms per cubic metre (ug/m3).

When the levels of PM2.5 go above 300 ug/m3 and PM10 breach 500 ug/m3, pollution is considered as “severe plus” or emergency. The corresponding 24-hour safe limits of these ultrafine particulates are 60 and 100.

No respite in sight

According to CPCB’s air lab chief Dipankar Saha and SAFAR’s prediction, the concentration of particulate matter will gradually rise over the next few days.

Saha said that falling wind speed, from Saturday’s 7 km/hour to 3 km/hour on Sunday, and rising moisture levels are behind the spike in pollution as in the absence of dispersion, local emissions are only leading to accumulation of pollutants.

During winter, as temperature drops, pollutants are trapped near the surface due to a slew of meteorological factors. Factors such as high wind speed and bright sunshine mitigate its impact to some extent.

Earlier this month, on November 9, the AQI had turned 486 as PM levels breached the emergency limits. Authorities announced a set of sweeping measures such as closure of schools and ban on entry of trucks and construction activities to deal with the “health emergency”.