Why is Delhi’s air quality so poor?

Why is Delhi’s air quality so poor?

Delhi’s air quality become progressively worse as it entered the “very poor” category for the first time this season. The overall air quality index (AQI) of the different parts of the city has been reproduced in the table below.
What are the primary causes of outdoor and indoor air pollution in New Delhi?
(i) The primary causes of outdoor air pollution are solid, liquid particles called aerosols & gases from vehicles emissions, construction activities, factories, burning stubble & fossil fuels, burning firecrackers and wildfire, etc.
(ii) Main causes of indoor air pollution are harmful gases from cooking fuels (such as wood, crop wastes, charcoal, coal and dung), damp, mould smoke, chemicals from cleaning materials, etc.
In expert’s findings the worst air quality is mainly due to the seasonal weather and climatic conditions. With winter setting in, calm wind conditions, shallow mixing layer height and low temperature cause accumulation of pollutants. Low temperature makes the wind heavier which slows the dispersion of pollution. In recent the deterioration in air quality was primarily due to a dip in mercury levels of Delhi and due to calmer winds.
Even after government/judicial orders against burning firecrackers, there was hardly any improvement in air quality in Delhi. As reported by reputed scientific bodies such as TERI (The Energy and Resources Institute), IIT Kanpur, SAFAR (System for Air Quality and Weather Forecasting and Research) GoI have all shown that firecrackers do not contribute to air pollution in any significant way. They aren’t even in the top 15 causes of pollution.
The seasonal stubble burning which is rampant in whole of Punjab and parts of Haryana at this time of the year plays a far bigger part in Delhi’s pollution woes than firecrackers.
Stubble burning is a seasonal problem, and in the period that it is prevalent, can cause anywhere between 20%-50% of the overall air pollution loading,” said Krishna. “If you average out all the sources over the period of a year, the contribution of stubble burning and other biomass burning would come down further.”
The impact of this stubble burning varies with wind direction. As per SAFAR, during November 4-6 (Diwali and the next two days), the share of stubble burning in PM2.5 is expected to be in the range of 20-38% as the wind direction is likely to change to north-westerly.
Likewise, power plants, industry, automobile sector are untouchable as they are considered ‘indispensable’ and have strong lobbies.

Stubble burning in a field in Punjab.

There has always been hue and cry that main cause of air quality deterioration in Delhi is stubble burning, but on November 15, the central government submitted an affidavit to the Supreme Court saying stubble or crop-residue burning contributed to only 4% of air pollution in Delhi.

While the affidavit said the contribution was 4% in winters and 7% in summers, another section in the same affidavit said that paddy stubble burning contributed 35%-40% to the capital’s particulate matter 2.5 and PM 10 concentrations. This caused an indignation, among sections of the media and experts in the air pollution domain on the actual contribution of stubble burning to Delhi’s severely deteriorating air quality. While it is not the main cause of pollution in winters, it is definitely an episodic problem, say experts.

Experts also focussed on major sources other than agricultural fires that contributed significantly to air quality deterioration in Delhi and National Capital Region. As per the Centre for Science and Environment’s analysis of total pollution sources to PM2.5 in Delhi between October 24 and November 8, the capital’s local sources reported 31%, of which Delhi’s transport sector accounted for more than half (51%) of its local pollution sources. This is followed by household pollution (13%), industries (12%) and construction (7%).

Anumita Roychowdhury, executive director (research and advocacy), Centre for Science and Environment, said, “We have hit the first ‘very poor day’ of the season. Air quality is expected to worsen with winter conditions hardening and trapping pollution. We need a clear strategy in Delhi and across the region to prevent a full-blown smog episode.”

The Supreme Court on Monday Nov. 15, stated that the major causes of air pollution in Delhi are industries, power, vehicular traffic and construction, and not stubble burning as was sought to be projected.

Farmer organizations had demanded to decriminalize stubble burning by farmers. Govt of India has accepted this demand as well: Union Agriculture Minister Narendra Singh Tomar Tweeted on Nov. 27

Besides, the government’s own real-time data published by the System of Air Quality and Weather Forecasting And Research and The Central Pollution Control Board show a much higher figure. SAFAR’s data show that the daily contribution varied between 7% on November 1 to 48% on November 7 with the latter figure being the highest till date this year. These dates coincide with this year’s Diwali celebrations which clearly add to the pollution but there is also another reason for the rise in pollution. 

How do we calculate Air Quality Index?

Air Quality Index (AQI) is a numerical value indicative of the aggregate levels of major pollutants in the ambient air. The more the AQI value, the more polluted the ambient air. It is descriptive of the magnitude of air pollution at a particular location.

AQI Calendar 0 -50 Good; 51 – 100 Moderate; 101 -150 Poor; 

151 -200 Unhealthy; 201 – 300 Severe; 301 -500 Hazardous

Smog in New Delhi a day after Diwali. Photo credit: Manvender Vashist/ PTI

Air Quality Index of Delhi and NCR

How harmful is indoor air pollution in New Delhi and why?

Indoor air pollution in New Delhi is as dangerous as outdoor pollution, because the air pollutants come inside the houses or buildings through doors, windows and ventilation.

What is the solution for indoor air pollution in New Delhi?

You must use an air purifier or fresh air machine at home or office indoor and close all the doors, windows and ventilations when the outdoor air quality index (AQI) in New Delhi is very high. Proper ventilation is highly recommended only when outdoor air quality is improving and moderate AQI range.