Article 1: Changing Air Pollution Patterns – Rise of Ground-Level Ozone
Why in News: A new air quality dashboard based on Central Pollution Control Board data highlights a shift in pollution trends—decline in NO₂ and CO but a rise in ground-level ozone across Delhi-NCR.
Key Details
- Long-term data since 2015 shows declining trends in nitrogen dioxide (NO₂) and carbon monoxide (CO). This indicates improvements in combustion-related emissions due to better fuel standards and regulations.
- Ground-level ozone is emerging as a major pollutant, especially during summer months. This reflects a shift from primary pollutants to secondary pollutants in urban air quality.
- PM2.5 and PM10 levels show seasonal peaks, especially during winter months. These peaks are influenced by meteorological conditions like low wind speed and temperature inversion. Decline in Primary Pollutants: PM2.5 levels dropped from 117.5 µg/m³ (2015) to 96.4 µg/m³ (2025), while PM10 fell from 244 µg/m³ to 197 µg/m³.
- Pollution trends are not uniform, with nearby NCR cities showing worsening conditions. This highlights the regional nature of air pollution and need for coordinated policy action. Shift in Pollutants: Annual average ozone in Delhi rose from 52 µg/m³ in 2021 to 66 µg/m³ in 2025.
Air Pollutants: Types and Sources
- Primary Pollutants: These are directly emitted from sources like vehicles and industries. Examples include NO₂, CO, PM2.5, and PM10, mainly from combustion and dust sources.
- Secondary Pollutants: These are formed through chemical reactions in the atmosphere. Ozone is a key secondary pollutant formed under sunlight from precursor gases.
- PM2.5 vs PM10: Fine particles (PM2.5) penetrate deep into lungs, while PM10 affects upper respiratory tract. Both are harmful and contribute significantly to health issues and reduced visibility.
- Sources of Pollution: Vehicles, industries, construction dust, and biomass burning are major contributors. Seasonal factors like stubble burning also intensify pollution levels in North India.
Ground-Level Ozone: Formation and Risks
- Photochemical Reaction: Ozone forms when NOx and volatile organic compounds react in sunlight. This makes it more prominent during hot and sunny conditions, especially in summer.
- Not Directly Emitted: Unlike other pollutants, ozone is not released directly into the air. It is formed secondarily, making it harder to control through direct emission reduction.
- Health Impacts: High ozone levels can cause respiratory issues and aggravate asthma. It also reduces lung function and affects vulnerable populations like children and elderly.
- Environmental Impact: Ozone damages crops and reduces agricultural productivity. It also affects ecosystems and contributes to climate change.
Seasonal Variability of Pollution
- Winter Peak: Pollution levels rise sharply between October and February. This is due to temperature inversion and stagnant air that trap pollutants near the surface.
- Monsoon Dip: Rainfall and strong winds help disperse pollutants. However, this does not necessarily mean emissions have reduced significantly.
- Summer Ozone Peak: Ozone levels rise during March–June due to strong sunlight. This creates a new seasonal pollution challenge distinct from winter smog.
- Meteorological Influence: Weather conditions play a key role in pollution levels. They determine dispersion, concentration, and chemical reactions in the atmosphere.
Trends in Delhi-NCR Pollution
- PM2.5 and PM10: Levels have slightly declined but remain above safe limits. This indicates partial success of policies but highlights persistent pollution challenges.
- Decline in NO₂ and CO: Long-term reduction reflects better emission standards like BS-VI norms. It also shows impact of cleaner fuels and improved industrial regulations.
- Rise in Ozone: Ozone levels have increased significantly in recent years. This points to the complexity of air pollution control in urban environments.
- Regional Variation: Cities like Meerut, Noida, and Ghaziabad show rising pollution trends. This indicates that pollution control must go beyond city-level interventions.
Urban Air Pollution and Governance Issues
- Fragmented Governance: Multiple agencies handle air quality, leading to coordination gaps. This reduces the effectiveness of pollution control measures.
- Construction and Dust: Rapid urbanisation increases dust pollution significantly. Lack of regulation and monitoring worsens PM10 levels.
- Vehicular Emissions: Increasing vehicle numbers contribute to pollution load. Though cleaner fuels help, total emissions remain high due to volume.
- Policy Gaps: Existing policies focus more on primary pollutants than secondary ones like ozone. This creates new challenges in air quality management.
Government Initiatives
- National Clean Air Programme (NCAP): Aims to reduce PM pollution levels by 20–30%. It focuses on city-specific action plans and monitoring systems.
- BS-VI Norms: Stricter emission standards for vehicles have reduced NO₂ and CO emissions. These norms align India with global best practices.
- Graded Response Action Plan (GRAP): Implements emergency measures during severe pollution. It includes restrictions on construction and vehicle use.
- Air Quality Monitoring: Expansion of monitoring stations improves data availability. This helps in better policy planning and real-time interventions.
Challenges Ahead
- Rising Secondary Pollutants: Ozone is difficult to control due to its formation process. It requires integrated reduction of precursor gases.
- Regional Coordination: Pollution spreads across state boundaries in NCR. This demands cooperative federalism and joint action plans.
- Data and Awareness: Lack of public awareness about ozone pollution remains a concern. Better communication strategies are needed for behavioural change.
- Climate Linkages: Air pollution and climate change are interconnected issues. Policies must address both simultaneously for long-term sustainability.
Way Forward
- Integrated Pollution Control: Address both primary and secondary pollutants together. This requires a multi-sectoral and scientific approach.
- Regional Strategy: Strengthen coordination among NCR states. A unified policy framework can improve effectiveness.
- Technological Solutions: Promote clean energy, electric vehicles, and dust control technologies. This will reduce overall pollution load.
- Public Participation: Increase awareness and citizen involvement. Behavioural changes can significantly contribute to pollution reduction.
Conclusion
Delhi’s pollution profile is shifting from traditional pollutants to complex secondary pollutants like ozone. While progress has been made in reducing NO₂ and CO, rising ozone levels pose new challenges. A comprehensive and adaptive policy approach is essential to tackle evolving air pollution dynamics.
EXPECTED QUESTIONS FOR UPSC CSE
Prelims MCQ
Q. Which of the following pollutants is classified as a secondary pollutant?
(a) Carbon monoxide
(b) Nitrogen dioxide
(c) Ozone
(d) Sulphur dioxide
Answer: (c)
Descriptive Question
Q. “India’s air pollution problem is shifting from primary pollutants to secondary pollutants like ozone.” Examine the causes, implications, and policy challenges. (250 words)