- A recent study has highlighted rising surface ozone pollution in Delhi during summer, making summer pollution as serious as winter smog.
About Ozone Pollution
- Meaning: It refers to the accumulation of ozone gas (O₃) near the Earth’s surface, formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react under sunlight.
- It is a secondary pollutant, meaning it is not directly emitted but produced through chemical reactions.
- Ozone’s Forms: Stratospheric ozone (“good”), which forms the protective ozone layer shielding Earth from UV radiation, and Tropospheric ozone (“bad”), a harmful pollutant.
Current Status
- Ozone Exceedance: Highest in Delhi-NCR and Mumbai, often breaching safe limits (CPCB, 2025).
- Seasonal Peak: Ozone levels in Delhi peak between March and May, driven by high temperatures and strong sunlight.
- Hotspot Area: Lutyens’ Delhi is a summer ozone hotspot despite extensive greenery, owing to high-emitting BVOC trees.
- Historical Data: In 2019, ozone exceeded 50 ppb on ~91% of summer days; in 2020, extreme heat was lower, and ozone episodes were reduced.
Causes of Ozone
- Chemical Reaction: Ozone forms when nitrogen oxides (NOx) react with Volatile Organic Compounds (VOCs) under sunlight.
- Human Emissions: Vehicles, industries, and power plants release NOₓ and VOCs.
- Biogenic VOCs: High – Biogenic Volatile Organic Compounds (BVOCs) trees like Ficus, Phyllanthus, and Bauhinia emit VOCs under heat and sunlight.
- Vegetation Gap: Few low-BVOC species (Amla, Babul, Bael) amplify local ozone hotspots.
- Temperature Effect: “Hot days” accelerate BVOC emissions and intensify ozone formation.
- VOCs are carbon-based gases that readily evaporate into the atmosphere from sources such as fuels, solvents, paints, industrial processes, and vehicle emissions.
- BVOCs are volatile organic compounds naturally emitted by plants and trees into the atmosphere.
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Impacts of Summer Ozone Pollution
- Health Impact: Ground-level ozone aggravates asthma and lung diseases. E.g., ~1 million premature deaths annually are attributed to ozone exposure (WHO).
- Agricultural Loss: Ozone reduces crop productivity. E.g., 5–15% yield losses in wheat and rice in South Asia (UNEP).
- Vegetation Damage: High ozone levels impair photosynthesis and plant growth, weakening urban forests and natural ecosystems.
- Climate Forcing: Surface ozone is a short-lived climate pollutant contributing ~0.4°C to global warming (IPCC).
Challenges in Addressing Summer Ozone Pollution
- Invisible Risk: Ground-level ozone is colourless and odourless, making it difficult for citizens and policymakers to detect or perceive its threat.
- Complex Formation: Ozone formation depends on multiple factors, including NOₓ, VOCs, sunlight, temperature, and vegetation, making prediction and control challenging.
- Climate Amplification: Rising temperatures, heatwaves, urban heat islands, and shifting El Niño–La Niña cycles intensify ozone formation in summer.
- Policy Limitations: Air pollution policies in India largely focus on winter particulate matter (PM2.5/PM10), leaving summer ozone inadequately addressed.
Solutions and Policy Measures
- Emission Control: Reduce NOₓ and VOC emissions from vehicles, industries, power plants, and biomass burning.
- Clean Energy: Promote renewables, electric mobility, and BS-VI fuels to lower fossil fuel combustion.
- Urban Greening: Plant low-BVOC trees (amla, babul, bael) instead of high-emitting species like ficus.
- Ozone Monitoring: Expand air quality monitoring and early-warning systems for timely alerts during high-ozone days.
- Policy Integration: Align climate mitigation and air-quality policies to reduce greenhouse gases and ozone precursors simultaneously.
Summer ozone pollution shows that clear skies do not always mean clean air. Tackling this invisible threat needs integrated emission control, climate action, and ozone-sensitive urban planning.
Reference: The Indian Express
PMF IAS Pathfinder for Mains – Question 583
Q. Surface ozone is emerging as a major summer pollutant in Indian cities due to complex atmospheric reactions. Analyse the factors contributing to rising ground-level ozone and discuss its impacts on public health and the environment. (250 Words) (15 Marks)
Approach
- Introduction: Write a brief introduction about Surface ozone in India.
- Body: Write factors contributing to rising ground-level ozone, its impacts on public health and the environment, and the way forward.
- Conclusion: Emphasis on an integrated and coordinated approach to tackling the surface ozone as an invisible threat.
