Kolkata Leads Indian Metros in Air Quality: Kolkata has emerged as one of India’s best-performing metro cities in terms of air quality, according to a new study by the Centre for Science and Environment (CSE). The analysis highlights that the city has consistently recorded over 50% of its days each year as having “good air quality” — the highest among Indian metros — over a span of four years.
This notable achievement marks a significant turnaround for a city that was once plagued by high pollution levels and frequent air quality warnings.
Kolkata Leads Indian Metros in Air Quality: Understanding ‘Good Air’ Metrics
“Good air days” are classified based on India’s National Air Quality Index (NAQI), which measures pollutants such as PM2.5, PM10, NO₂, SO₂, CO, O₃, NH₃, and Pb. A “Good” AQI score ranges between 0-50, indicating minimal impact on public health even for sensitive individuals. The CSE’s report draws upon real-time monitoring data from the Central Pollution Control Board (CPCB) and regional pollution boards.
External source:
- National Air Quality Index: https://app.cpcbccr.com/AQI_India/
Kolkata’s Performance vs. Other Cities
Between 2020 and 2024, Kolkata consistently outperformed other major Indian metros, including Delhi, Mumbai, Chennai, Hyderabad, and Bengaluru, in terms of the number of “good air days.” In 2023-24 alone, Kolkata recorded 351 good air days out of 356 monitored days, according to the CSE report.
This figure significantly contrasts with other metros such as Delhi, which continued to report dangerously high pollution levels, especially during winter months.
External source:
- Centre for Science and Environment (CSE): https://www.cseindia.org/
Why Kolkata Is Seeing Cleaner Air
Several contributing factors have helped Kolkata improve its air quality:
- Phasing out of old diesel vehicles and better enforcement of vehicular emission norms.
- Expansion of public transport infrastructure, including metro lines and electric buses.
- Dust control measures, especially during road construction.
- Banning of open burning in urban areas and stricter enforcement on illegal waste disposal.
- Tree plantation drives and creation of green corridors around urban centers.
- Regulatory pressure from both state and national environment boards.
Seasonal Patterns: Summer Gains, Winter Challenges
The report highlights a distinct seasonal trend in Kolkata’s air quality. The city performs much better in the summer and monsoon months, with an average PM2.5 level close to 30 µg/m³—well below the Indian standard of 40 µg/m³.
However, during winter, especially from November to January, pollution levels spike. December 2023 and January 2024 saw PM2.5 levels rise to 73 and 77 µg/m³, respectively. Despite this, these were the lowest winter pollution figures since 2019, indicating a long-term positive trend.
External source:
- World Air Quality Report by IQAir: https://www.iqair.com/world-air-quality-report
The Role of Secondary Pollutants
One of the key findings in the CSE report is the growing presence of secondary pollutants in Kolkata’s air. These include ammonium sulfate and ammonium nitrate, which are not directly emitted but form in the atmosphere from precursor gases like ammonia (NH₃), sulfur dioxide (SO₂), and nitrogen oxides (NOₓ).
In Kolkata, secondary pollutants contribute nearly one-third of PM2.5 concentrations, particularly in winter. These pollutants are harder to regulate and require more coordinated strategies, including control over agricultural practices and industrial emissions.
Rural-Urban Link: Agricultural Burning Adds to Pollution
Though Kolkata itself has managed urban emissions better in recent years, the impact of biomass burning in surrounding rural areas remains a concern. According to West Bengal Pollution Control Board data, more than 26,000 burn incidents were recorded in the 2023-24 season in districts adjacent to the city.
Smoke from crop residue burning and open waste fires often drifts into the urban atmosphere, adding to Kolkata’s pollution burden during colder months.
What Makes Kolkata’s Progress Unique
While other metro cities continue to grapple with worsening air pollution, Kolkata’s relative success can be attributed to:
- A more humid and coastal climate that disperses airborne pollutants.
- Fewer large-scale industries within city limits.
- Political will to implement bans and restrictions during peak pollution months.
- Strong public response and awareness campaigns about clean air practices.
Public Health Impacts and Future Steps
Despite improvements, Kolkata’s air quality still exceeds World Health Organization (WHO) guidelines, which recommend annual PM2.5 levels not exceeding 15 µg/m³. The Indian standard remains more lenient at 40 µg/m³.
According to public health researchers, air pollution remains a leading cause of respiratory illnesses, heart conditions, and premature deaths in urban India. Continuous exposure, even at moderate levels, can affect children, the elderly, and people with pre-existing conditions.
External source:
- WHO Air Quality Guidelines: https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health
To ensure long-term gains, experts suggest:
- Reducing NH₃ and SO₂ emissions to tackle secondary pollution.
- Enhancing public transport further and incentivizing electric vehicle adoption.
- Investing in rural air quality control programs, especially in agriculture-dominant areas.
- Scaling up air quality monitoring infrastructure and improving transparency.
Conclusion: A Model for Urban Air Governance
Kolkata’s progress in increasing the number of good air days sets a precedent for other Indian cities. While challenges remain—particularly during the winter months—the city’s data-driven policies, enforcement, and public cooperation have produced tangible results.
Maintaining this momentum will require continued vigilance, cross-sector collaboration, and a commitment to aligning India’s air quality standards with global benchmarks. If successful, Kolkata could soon become not just a national, but a global model for urban air governance.
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