NCR worst impacted by ozone pollution: CPCB to NGT

As per the analysis, there were 57 ambient air quality monitoring stations in NCR in 2023, out of which 25 exceeded the permissible national eight-hour standards of ozone by more than 2%. Whereas, in Mumbai, 22 out of 45 stations crossed the standards.

The Central Pollution Control Board (CPCB) has informed the National Green Tribunal (NGT) that National Capital Region (NCR) is the worst impacted in the country by high ozone (O3) pollution, followed by Mumbai Metropolitan Region (MMR). The board also said a Union environment ministry’s expert committee is being formed to study the health impacts.

CPCB attributed high levels in these regions to emissions from the transport sector, power plants, and industrial activities, which collectively contribute to the overall NOx emission load.

In an affidavit to the tribunal, the CPCB analysed 10 major regions across the country for ground-level ozone. As per the analysis, there were 57 ambient air quality monitoring stations in NCR in 2023, out of which 25 exceeded the permissible national eight-hour standards of ozone by more than 2%. Whereas, in Mumbai, 22 out of 45 stations crossed the standards.

The safe eight hourly standard for ozone is 100 micrograms per cubic metre (µg/m³) while the one-hourly standard is 180 µg/m³, the report said, stating the data was analysed for both 2023 and 2024, with only stations that exceeded the safe standards by more than 2% being flagged.

NGT in August last year, had taken suo motu cognisance of a news report, highlighting high ozone levels in the country. Subsequently, it had sought details from the central pollution body on the situation.

Comparing the level to the one-hour standard of ozone, CPCB said four stations each in NCR and MMR exceeded the limit in 2023, followed by one station in Pune.

In 2024, study between April and July found out 21 out of 57 NCR stations exceeded the one-hour standard, while none crossed the standard in Mumbai.

“The Delhi-NCR and MMR reported higher exceedance of ozone concentration compared to other regions. The tropospheric or ground-level ozone is formed primarily from complex non-linear photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOx). Besides, carbon monoxide (CO) and methane (CH4) emitted by residential and agricultural sources also play a role in ozone formation..” said the report dated September 25.

While the O3 layer in the stratosphere helps absorb most of the Sun’s harmful ultraviolet radiation, at the ground-level, it is a highly reactive and toxic gas, which can cause various health problems like coughing, throat irritation, chest pain and congestion.

CPCB attributed high levels in these regions to emissions from the transport sector, power plants, and industrial activities, which collectively contribute to the overall NOx emission load.

“Additionally, ozone precursors may also originate from natural sources, including biogenic emissions of volatile organic compounds (VOCs), soil-based emissions of NOx, wildfire-induced emissions of carbon monoxide (CO), and methane emissions from the biosphere,” the report added.

Besides Delhi-NCR and Mumbai, other regions assessed by the CPCB were Chennai, Pune, Greater Lucknow, Greater Jaipur, Kolkata, Greater Hyderabad, the Bengaluru Metropolitan area, and Ahmedabad.

Referring to NGT’s August 28 order, CPCB said the environment ministry was granted four weeks’ time to provide a list of experts who will study the health impact of rising ozone pollution. The committee will be formed before the next hearing on November 11, CPCB said.