Delhi's air quality "improved significantly" on Wednesday as overnight rains washed away bigger pollutants even as the Supreme Court-appointed EPCA recommended implementation of either the odd-even scheme or imposition of a complete ban on non-CNG private vehicles if the pollution level in the city spikes again.
As stubble burning in the neighbouring states declined, contributing just three per cent -- the lowest this month -- to pollution, EPCA chairman Bhure Lal shot off a letter to pollution watchdog CPCB, asking them to consider implementation of either the odd-even scheme or impose a complete ban on non-CNG private vehicles.
Reacting to the recommendation, the Central Pollution Control Board (CPCB) said this matter of additional steps, including implementation of a complete ban on private vehicles, should be deliberated by the EPCA which is a larger body.
"It will be worthwhile if the measures already under implementation and suggestions on additional steps are discussed by the EPCA," the task force said in response to EPCA recommendation on ban of non-CNG private vehicles.
Though the conditions provided some respite to the city which has been reeling under 'severe' pollution for the past one week, the air quality was still far from safe and fell in the 'poor' category with Air Quality Index (AQI) of 285.
The AQI has been oscillating between 'severe' and the upper range of 'very poor' for the past one week even crossing 600 post-Diwali.
According to the Centre-run System of Air Quality and Weather Forecasting (SAFAR), the contribution of stubble burning to the pollution in Delhi has been recorded the least on Wednesday for this month at 3 per cent. On November 5, the contribution of stubble burning was the highest this month at 33 per cent.
On Wednesday, the PM2.5 -- particles in the air with a diameter of less than 2.5 micrometres -- level was recorded at 140, while the PM10 -- particles in the air with a diameter of less than 10 micrometres -- was recorded at 232 in Delhi, according to data by the Central Pollution Control Board.
Fourteen areas in Delhi recorded 'very poor' air quality while 20 areas showed 'poor' air quality, the CPCB said.
Similar conditions are likely to prevail in the coming days, according to SAFAR.
An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
In a letter to CPCB member secretary Prashant Gargava, Lal said all cities, which have similar emergency plans -- like Paris or Beijing -- include restrictions on private vehicles, which is done by either number plate or by fuel type or its age.
He said vehicles contribute as much as 40 per cent of the total emission load in Delhi and roughly 30 per cent in the region.
"In this situation, the only option is to look at either a complete ban on all private vehicles (without the identification of petrol or diesel), other than CNG and/or restriction on plying by number plate (odd-even)," he said.
"However, please note that the odd-even scheme, as practiced in other cities for similar pollution abatement, is done for extended hours and includes all private vehicles," he added.
In 2016, the odd-even scheme was enforced twice -- January 1-15 and April 15-30 -- in Delhi when vehicles having odd and even numbers were allowed to ply on alternate days as the air quality deteriorated.
The odd-even scheme is a part of the Graded Responde Action Plan (GRAP), emergency measures implemented in phases to combat air pollution. It came into effect from October 15.
Lal said he understands that any restriction on plying of private vehicles without adequate public transport would create "huge inconvenience" to people.
"Even after removing trucks and other diesel commercial vehicles, which are the highest segment of this pollution load, the remaining vehicles add up to substantial load, particularly private diesel vehicles which contribute substantially to both NOx (nitrogen oxides) and PM (particulate matter) emission," the EPCA chairperson said.
In a meeting called to discuss the suggestion made by Lal over ban of non-CNG private vehicles, the task force asked authorities to "discuss the additional steps such as these".
The task force also recommended strict enforcement by concerned agencies must continue.
"Emissions must be curtailed during night time when dispersion of air pollutants is limited. For this, agencies must be on alert and ensure necessary action. For this, agencies must be on alert and ensure necessary action," the minutes of the meeting said.
The meeting was chaired by Gargava and attended by other members of task force which includes officials from the India Meteorological Department (IMD), Uttar Pradesh State Pollution Control Board, Delhi Pollution Control Committee, Rajasthan State Pollution Control Board, among others.
The SAFAR said air quality has "improved significantly mainly due to sufficient rainfall last night that washed away bigger particles and created space for faster dispersion without decline in temperature".
This is mainly due to the fact that surface winds are still low and temperature is likely to cool down, it said.