Air

Apolcaypse now: Toxic air shrouds Delhi

Delhiites breathed the season’s worst PM2.5 on the morning of November 3, 2019

 
By Shagun Kapil
Last Updated: Sunday 03 November 2019
Delhi November 3, 2019. Photo: Joyjeet Das

Delhi on November 3, 2019 was shrouded in toxic haze as air pollution levels were completely off the charts. 

Alarmingly, the level of particulate matter (PM) in the air was at least seven times more than the prescribed World Health Organisation (WHO) standard. In fact, Delhiites breathed the season’s worst PM2.5 on Sunday morning. These ultrafine particles are capable of entering the respiratory system and reach the bloodstream through human lung and blood tissues.

While overall Air Quality Index (AQI) according to SAFAR (System of Air Quality and Weather Forecasting And Research) website, under the Union Ministry of Earth Sciences, was recorded at 625 on Sunday morning, the concentration of harmful pollutants PM10 and PM2.5 were at 648 and 475 microgramme per cubic metre (ug/m3) respectively. 

An AQI between 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.  

The prescribed standard for PM10 and PM2.5 is 100 and 60 ug/m3 respectively. 

As per analysis by SAFAR scientists, the light drizzling on Saturday night and Sunday morning, in a calm wind condition, worked highly adversely in deteriorating air quality and season’s highest level of AQI of PM2.5 was recorded as rapid secondary aerosol formation started in the wee hours. 

This led to an increase of share of PM2.5 in PM10 to more than 80 per cent as against 50 per cent in normal course. 

Drizzling made air-holding capacity high and the mixing layer height became season’s lowest (50 metres), which aggravated the situation further. 

The readings at monitoring stations across the town showed hazardous air quality levels At 11 AM, the real time AQI was 999 at monitoring stations at many places including Bawana, Major Dhyan Chand Stadium, Narela, Alipur, Patparganj, Punjabi Bagh, Mandir Marg, Pusa, Shahdara, Sriniwaspuri, and Anand Vihar.  

A drastic reduction recorded in effective stubble fire counts of northwest India (Haryana and Punjab) during the last 24 hours (57), according to SAFAR. 

However, the analysis also said that one of the reasons of low count could be that the region was under dense cloud cover, which obscures active fire detections by satellite. 

“Although upper winds are north-westerly, if satellite counts to be believed, the biomass intrusion was limited and confined to less than 17 per cent, as per SAFAR-model,” it said. 

The Western Disturbance (WD) as a cyclonic circulation was still persisting and may increase wind speed and boundary layer height by Monday, which is likely to positively influence Delhi’s air quality.

There might be a little relief by late Sunday evening as boundary layer could go up.

“Such rapid built-up does not last long and likely to recover as the sunlight will come and boundary layer will go up which is expected by late evening today under current situation. The AQI is expected to remain in ‘severe’ category until early November 4 but likely to be recovering further by late November 4 to the upper end of ‘very poor’,” it said.  

Also read: Air pollution in Delhi: Act for your children's sake

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