Air quality plunges to 'severe' category

New Delhi, November 12

The noxious haze returned to Delhi and its suburbs on Tuesday due to raging farm fires in neighbouring states and a fall in temperature and the wind speed.

Weather experts said the national capital recorded a minimum of 11.7 degrees Celsius, the season's lowest so far on Tuesday morning. It is two notches below normal for this time of the year.

A dip in the wind speed and temperature makes the air denser, leading to accumulation of pollutants, said Kuldeep Srivastava, head of the India Meteorological Department's regional weather forecasting centre.

On Tuesday, Delhi's overall air quality index read 417 at 12.30 pm. It was 360 at 4 pm on Monday.

The levels of PM 2.5 -- tiny particulate matter less than 2.5 microns in diametre that can enter deep into lungs and even the bloodstream -- shot up to 292 micrograms per cubic metre, around five times the safe limit of 0-60 micrograms per cubic metre.

The levels of PM10 increased to 436 micrograms per cubic metre, more than four times the safe limit of 100 micrograms per cubic metre.

Most of the 37 air quality monitoring stations across Delhi recorded air quality in the “severe” category.

Bawana was the most-polluted area in the city with an AQI of 445, followed by Anand Vihar (442), Wazirpur (442) and Dwarka Sector-8 (442).

Faridabad (404), Ghaziabad (445), Greater Noida (436), and Noida (436) also choked on extremely polluted air.

An AQI between 201 and 300 is considered “poor”, 301-400 “very poor” and 401-500 “severe”. An AQI above 500 falls in the “severe plus” category.

Experts said the spike in pollution levels could be attributed to a significant decline in the wind speed -- from 20 km per hour over the last two days to 10 km per hour on Monday and Tuesday.

Incidents of stubble burning in Haryana and Punjab have increased and northwesterly winds have been bringing more farm fire plume to the Delhi-NCR region, they said.

Stubble plume intrusion is expected to increase and a decrease in surface wind speed over the Delhi region is predicted for the next two days.

According to the government's air quality monitor, SAFAR, the share of stubble burning in Delhi's pollution is predicted to be 25 per cent on Tuesday, up from 18 per cent on Monday.