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.
"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.
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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).
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.
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.
"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.
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