Observing that air quality in the national capital was "severe" for most of the month, the National Green Tribunal has directed implementation of a graded response action plan to combat different levels of air pollution.
The apex environment watchdog said there was no uniformity and "unanimity" in action plans of the Central Pollution Control Board (CPCB) and the Supreme Court appointed Environment Pollution Control Authority (EPCA).
The air-quality categorisation needs "clarity and certainty", it said in its order recently.
"The statistics clearly shows that all the time, the ambient air quality of NCT of Delhi is polluted and for most of the period of the month it is severe and above. This is the quality of air that we are providing to the people living in NCR Delhi and NCT of Delhi. It is a clear violation of their fundamental right," said a bench headed by former chairperson Swatanter Kumar.
The tribunal said an approach which is precautionary and preventive rather than curative has to be adopted.
"Importantly, the authorities are bound to take recourse of precautionary principle and ensure decent and clean environment to the public at large, living in NCR Delhi and in fact all over the country," it said.
The tribunal said there was no dearth of laws, guidelines and directions in relation to prevention and control of pollution of the ambient air quality in Delhi. What is required is the implementation of laws and directions.
The NGT divided air pollution into four categories -- Category I (Average), II (Severe), III (Critical) and IV (Environmental Emergency).
While category I action plan would come in force when PM10 is more than 100 micrograms per cubic meter but less than 300 and PM2.5 is more than 60 but below 180, category II will be in action when PM10 is more than 300 g/m3 but less that 700 g/m3 and PM2.5 is more than 180 but below 400 g/m3.
Category III would be implemented when PM10 is more than 700 micrograms per cubic meter but below 1000 g/m3 and PM2.5 is more than 400 g/m3 but less than 600 g/m3 and environmental emergency would be termed when PM10 is above 1000 g/m3 and PM2.5 is above 600 g/m3.
While CPCB has formulated six categories, which refer to different levels of pollution -- good, satisfactory, moderately polluted, poor, very poor, severe and above severe -- EPCA's action plan, termed GRAP, has formulated five categories. These are severe plus or emergency, severe, very poor, moderate to poor and moderate.
NGT has sought the implementation of odd-even in the third category, but the current GRAP calls for the move at the emergency or highest stringency levels.
Terming as "critical" levels of pollution in the third category, the NGT said immediate steps, including a ban on construction and introduction of the odd-even scheme, should be implemented by the authorities.
When air pollution reaches environmental emergency levels, thermal power plants in Delhi should be shut down and sprinkling of water from the high-rise buildings should be done, the tribunal said.
"There shall be complete prohibition on use of diesel generator sets. The trucks and heavy vehicles carrying material including trailers shall be prohibited from entering NCT of Delhi.
"Only the heavy vehicles carrying essential goods like medicine, food etc. would be permitted, while all other heavy vehicles will not be permitted to enter NCT of Delhi for the duration of environmental emergency," the NGT said.
The tribunal had on December 6 slammed the AAP government and neighbouring states over their action plan on ways to deal with severe air pollution in the city and directed them to file a detailed document to tackle the problem.
It had observed that air pollution was never at "normal level" in the national capital and directed the neighbouring states of Punjab, Haryana, UP and Rajasthan to file the action plan afresh.
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