Ground-Level Ozone Pollution in India’s Major Cities

The Central Pollution Control Board (CPCB) recently reported alarming levels of ground-level ozone pollution in India’s urban regions. The National Capital Region (NCR) faces the highest ozone concentrations, followed by the Mumbai Metropolitan Region (MMR). This has raised concerns due to ozone’s harmful effects on health and the environment.

Ozone Pollution Overview

Ground-level ozone is a toxic air pollutant formed by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). These reactions are intensified by sunlight. Unlike the protective ozone layer in the stratosphere, surface ozone harms respiratory health and vegetation.

Regions Most Affected

CPCB analysed ozone data from 10 major Indian regions during 2023 and early 2024. NCR recorded the highest exceedances, with 25 of 57 monitoring stations surpassing the national eight-hour ozone limit of 100 micrograms per cubic metre by over 2%. MMR followed with 22 of 45 stations exceeding the same limit. Other cities like Pune, Chennai, and Bengaluru showed comparatively lower but notable ozone levels.

Ozone Standards and Breaches

India’s ambient air quality standards set an eight-hour ozone limit at 100 µg/m³ and a one-hour limit at 180 µg/m³. In 2023, four stations each in NCR and MMR and one in Pune breached the one-hour standard. During summer 2024, 21 NCR stations exceeded the one-hour limit, while Mumbai stations remained within safe levels.

Sources of Ozone Precursors

Ozone forms from precursors such as NOx and VOCs emitted by vehicles, power plants, and industries. Residential and agricultural activities contribute carbon monoxide (CO) and methane (CH₄), which also promote ozone creation. Natural sources include biogenic VOCs, soil emissions of NOx, wildfires producing CO, and biosphere methane emissions.

Health and Environmental Impact

Ground-level ozone causes coughing, throat irritation, chest pain, and congestion. Long-term exposure worsens respiratory illnesses like asthma. It damages crops and forests, reducing agricultural productivity and biodiversity. Urban areas with high traffic and industrial activity face greater risks.

Regulatory and Monitoring Efforts

The National Green Tribunal (NGT) took suo motu cognisance of ozone pollution after media reports brought into light the issue. CPCB’s extensive monitoring helps identify pollution hotspots and trends. Stricter emission controls and cleaner technologies are needed to reduce precursor emissions and improve air quality.