The tribunal also sought a fresh report from the CPCB, which had to mention how effectively the measures of the Centre were being implemented.
The National Green Tribunal has sought a response from the Centre on the "feasibility and mechanism" for implementation of the CPCB's recommendations for controlling ozone levels, which were found beyond the permissible limits in some areas of the national capital.
The green body earlier directed the Central Pollution Control Board (CPCB) and other agencies to submit relevant material explaining why ozone levels in these areas exceeded permissible limits. It had also sought "targeted approaches" that could be adopted for these areas.
In an order dated December 23, a bench of NGT Chairperson Justice Prakash Shrivastava and expert member A Senthil Vel noted that the CPCB had submitted a report dated December 20 about the measures for control of ozone levels along with some suggestions or recommendations.
The CPCB report said, "It has been recognised globally that control of ozone is only possible through control of its precursors. It is also evident that control of local sources of its precursors may not yield significant benefits in terms of ozone reduction, as both ozone and its precursors can be transported over hundreds of kilometres."
"Considering the same, the government has undertaken several initiatives at the national level, to control the precursors of ozone, i.e, nitrous acid (NOx), volatile organic compound (VOC), methane and carbon monoxide (CO) to some extent," it said.
The tribunal noted the report about the government’s National Clean Air Programme (NCAP) of 2019, aimed at reducing air pollution levels across the country, where city-specific clean air action plans had been prepared and rolled out for implementation in 130 non-attainment million-plus cities to improve the air quality.
It also noted the report about various action plans by the Urban Local Bodies (ULBs) to control NOx emissions as part of the NCAP and that various waste management rules were being implemented to prevent VOC, CO and methane emissions.
The tribunal noted that the report also mentioned specific interventions for the sectors of transport, power plants and industries, besides the measures for preventing biomass burning, especially paddy straw burning in northern India.
It said along with the Union government controlling ozone concentrations through control of their precursors at national or regional levels, the pollution board's report mentions various suggestions.
The tribunal noted the CPCB’s suggestion that "considering the elevated levels of ozone observed during COVID-19 lockdown and that the ozone concentration is also influenced by transboundary movement, soil and biogenic emissions, a detailed study may be required with help of air quality experts to evaluate the reasons for higher ozone levels at various locations in Delhi."
It also noted that the CPCB had discussed the issue with air quality experts, who said that a study was required.
"The feasibility and mechanism for implementation of recommendations made by CPCB needs consideration. Hence, we deem it proper to implead the following as respondent, the Union Ministry of Environment Forest and Climate Change through the secretary," the tribunal said.
"Let notice be issued for filing the response by way of affidavit, especially commenting upon the recommendations that have been made by CPCB," it added.
The tribunal also sought a fresh report from the CPCB, which had to mention how effectively the measures of the Centre were being implemented.
The matter has been posted on April 21 for further proceedings.
The NGT had taken suo motu cognisance of a news report regarding the elevated ozone levels.
During the hearing in September, the NGT noted that as per a Delhi Pollution Control Committee (DPCC) report, ozone concentrations surpassed national standards at seven monitoring stations in Delhi last year while nine stations recorded similar breaches during this summer.
The DPCC’s report highlighted that dangerous levels of ground-level ozone were recorded in several traffic-heavy areas during April and May 2023. Nehru Nagar witnessed 56 days of high ozone levels, Patparganj 45 days and Aurobindo Marg 38 days.
Nehru Nagar, located near Lajpat Nagar, recorded the highest concentration of ozone at 224.9 micrograms per cubic metre, far above the national standard of 100 micrograms per cubic metre during an eight-hour period.
Other peaks included 188.3 micrograms per cubic metre in Patparganj and 175.4 micrograms per cubic metre in RK Puram, according to the DPCC’s findings.