Delhi air remains 'severe plus'

Emergency persists despite drop in stubble burning 

By Shagun,
Published: Friday 15 November 2019
Air mask. Photo: Joyjeet Das

Air quality in Delhi was at ‘emergency’ levels again on November 15, 2019 — also the last day of the odd-even scheme.

The overall air quality index (AQI) crossed the 500 mark and was at 528 in the ‘severe plus’ or ‘emergency’ category at 10 AM on Friday, according to SAFAR (System of Air Quality and Weather Forecasting and Research).

An AQI of 0-50 is considered ‘good’, 51-100 ‘satisfactory’, 101-200 ‘moderate’, 201-300 ‘poor’, 301-400 ‘very poor’, and 401-500 ‘severe’. Above 500 is ‘severe-plus’, or ‘emergency’ category.

This even when the share of fresh stubble burning count in particulate matter (PM) 2.5 concentration in Delhi's air was forecast to fall to five per cent from November 14’s 13 per cent.

But existing PM in the air wasn’t being flushed out due to stagnation, low wind speed (around 4-5 kilometres per hour) and very low mixing height (where the lower atmosphere meets upper atmosphere, allowing dispersion).

Considering the life time of PM 2.5, a sustainable cumulative impact of stubble burning intrusion was estimated to be much higher owing mostly to meteorological factors, according to an analysis by SAFAR under the Union Ministry of Earth Sciences.

The sky over the Delhi region was likely to be cloudy and reduced solar radiation was likely to reduce heating and mixed layer growth, which has led to further deterioration of air quality.

Hazardous air quality was recorded at 32 monitoring stations of the Central Pollution Control Board (CPCB), the Delhi Pollution Control Committee (DPCC) and the India Meteorological Department (IMD). Data was not available for four.

AQI was close to 500 at Jawaharlal Nehru Stadium, Dwarka Sector 8, ITO, Nehru Nagar, Siri Fort, and Pusa.

The concentration of ultra fine harmful pollutants like PM2.5 and PM10 in air that the Delhiites are breathing rose substantially and was around six times over the prescribed safe standards. While PM10 was at 583 microgramme per cubic metre, PM2.5 was at 378. Safe standards were at 100 and 60 respectively.

An approaching fresh western disturbance existed as an induced cyclonic circulation over southwest Rajasthan and started to affect northwest India. Scattered rainfall was expected over Punjab, which was likely to lead to very low fire count during the next two days.  

Some improvement was expected by Friday afternoon and significant improvement by Saturday owing to a forecast of an increase in wind speed, which is likely to increase ventilation and ‘improve’ the air quality towards ‘very poor’.

A review of the air quality situation by the CPCB and Environment Pollution (Prevention and Control) Authority was due later in the day. Schools in Delhi-NCR remained closed for the second day.

The Delhi government was to take a call on whether to continue with odd-even scheme.

The scheme will anyway be in force if the air quality remains ‘severe plus’, according to the Graded Response Action Plan currently in force.

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