In eastern India, Kolkata stands as a city of deep cultural heritage and intellectual history, yet it now faces an escalating crisis of air pollution. Once celebrated for its artistic and academic vibrancy, the city of over four million residents is increasingly burdened by toxic gases and particulate matter that compromise daily life. A recent study led by Dr. Sumanta Das of the Ramakrishna Mission Vivekananda Educational and Research Institute, in collaboration with the West Bengal Pollution Control Board, offers one of the most comprehensive examinations yet of this invisible threat. Through the integration of five years of monitoring data, advanced geospatial techniques, and meteorological analysis, the research delivers a multidimensional portrait of Kolkata’s air and provides pathways toward targeted solutions.

The study is driven by an urgent national context: India accounts for 21 of the world’s 30 most polluted cities, and Kolkata consistently ranks among them. While Delhi’s notorious smog often dominates public attention, Kolkata’s long-term air quality dynamics have been less rigorously documented. Past studies tended to focus on specific seasons or short-term conditions, offering fragmented insights into a problem that unfolds continuously and is shaped by a range of human and climatic forces. Dr. Das and his team sought to bridge this gap by conducting a sustained, multi-year investigation that captures both the citywide extent of pollution and its shifting patterns over time.

What distinguishes this research is its methodological innovation. The team drew on data from thirteen manual air quality stations and seven automated continuous monitoring stations maintained by the Kolkata Municipal Corporation. These provided measurements of critical pollutants, including PM₂.₅, PM₁₀, nitrogen dioxide (NO₂), and sulfur dioxide (SO₂). Instead of analyzing these values in isolation, the researchers applied Inverse Distance Weighted interpolation, a geospatial method that transforms scattered readings into continuous surfaces. This enabled the creation of high-resolution pollution maps that reveal how contaminants accumulate and disperse across neighborhoods. By coupling these spatial models with meteorological records from the India Meteorological Department, the team was able to identify how weather and climate interact with emissions to shape Kolkata’s atmospheric health.

The results highlight persistent hotspots that encapsulate the diversity of Kolkata’s air quality challenges. Hide Road, an industrial belt adjacent to a thermal power plant; Shyambazar, a dense traffic interchange; Moulali, a mixed-use hub marked by informal waste burning; Ultadanga, a transport-heavy corridor with dense slums; and Minto Park, a construction-dominated commercial district—all consistently registered dangerous pollution levels. Each hotspot reflects a different facet of the problem: industrial emissions, vehicular congestion, informal settlement practices, or construction-related dust. These findings reveal that air pollution is not uniform but deeply tied to the city’s socioeconomic and spatial structures.

Particulate matter emerged as the most pressing pollutant. PM₁₀ levels routinely exceeded national safety thresholds, while PM₂.₅ concentrations in 2023 were particularly alarming, surpassing permissible limits at nearly every site. PM₂.₅ is especially dangerous due to its ability to penetrate deep into the respiratory system. High levels were recorded in Mominpur, Topsia, and Moulali—areas marked by a convergence of heavy traffic and informal housing. Nitrogen dioxide, primarily from vehicular combustion, spiked sharply in 2023, indicating a resurgence in emissions following the pandemic lockdowns. While sulfur dioxide was generally lower, its episodic surges in neighborhoods like Beliaghata, Behala, and Mominpur pointed to the continued role of small-scale industries and biomass burning.

The study also underscored the importance of meteorology as a governing factor in air quality. Pre-monsoon heat was associated with declines in PM₂.₅, likely due to enhanced vertical mixing and chemical breakdown in hotter conditions. Rainfall during the post-monsoon period acted as a natural purifier, washing pollutants from the air. Humidity, however, produced more complex effects: while it helped suppress particulate matter and nitrogen oxides, it correlated with higher sulfur dioxide levels during the monsoon, suggesting secondary chemical transformations. These nuanced seasonal dynamics demonstrate that Kolkata’s air cannot be disentangled from its climate rhythms, and effective management must align with these temporal cycles.

A particularly revealing aspect of the study was its ability to capture the pandemic’s imprint on the city’s air. In 2020 and 2021, lockdowns brought traffic and industry to a halt, and the air cleared significantly, offering residents a rare glimpse of a cleaner environment. Yet by 2023, as activity rebounded, pollution not only returned but in some areas exceeded pre-pandemic levels. This rebound highlights both the temporary nature of short-term improvements and the necessity of systemic reforms in sectors such as transport, industry, and waste management if lasting change is to be achieved.

Beyond documenting trends, the study contributes a framework for targeted policy action. By correlating pollutant profiles with neighborhood-specific conditions and meteorological drivers, it generates a detailed map of vulnerabilities and intervention points. Hide Road demands industrial emission control and cleaner energy transitions, Shyambazar and Ultadanga require transport reform and congestion management, Moulali calls for stricter regulation of waste burning and improved energy access in slum areas, while Minto Park illustrates the need for dust mitigation at construction sites and improved urban ventilation. These location-specific strategies move the discussion away from generic prescriptions toward precision-targeted governance.

The research also highlights the social inequities embedded in Kolkata’s pollution landscape. Many of the most polluted areas coincide with wards that have high concentrations of slum dwellers, who are simultaneously the most exposed and the least empowered to change conditions. Their reliance on biomass fuels and informal waste disposal contributes to emissions, but it also reflects structural inequalities in energy and housing access. By situating air pollution within these lived realities, the study frames clean air as both an environmental and social justice imperative.

Looking ahead, the scientists recommend strengthening Kolkata’s monitoring network through the integration of low-cost sensors and satellite-based observations to fill data gaps. They suggest employing advanced source apportionment methods such as Positive Matrix Factorization to precisely attribute pollutants to different sources. Coupling geospatial data with machine learning could further enhance predictive modeling, enabling early warning systems and proactive interventions. Such innovations would transform Kolkata into a model for sustainable urban air governance, with lessons applicable across the Global South.

 More information:

Chakroborty, B., Rudra, K., Chakrabarty, D. et al. Decoding spatiotemporal dynamics of air pollution and its underlying drivers in Kolkata metropolitan area through integrated field investigation and geospatial analysis. Discov Cities 2, 77 (2025). https://doi.org/10.1007/s44327-025-00118-7