A Month in Megacity Delhi: Caught in a Web? Stubbles, Firecrackers and Winter Weather

What the paper says

Thick haze, black smog, cold sun, choked lungs—winter of 2024 in the Indian capital of Delhi was no exception over recent earlier years—severe urban air pollution undermining agendas of multiple UN Sustainable Development Goals (UN SDGs), including Resilient Cities and Communities (UN SDG 11), Life on Land (UN SDG 15) and Good Health and Well-being (UN SDG 3). In this narrative, we track down six criteria—air pollutants, particulate matter (PM 2.5 , PM 10 ), carbon monoxide (CO), nitrogen dioxide (NO 2 ), ozone (O 3 ), and sulphur dioxide (SO 2 )—during the period 20 October to 18 November 2024, as measured at 39 monitoring stations, at 8:00 pm (IST). Results indicate that the daily median concentrations ( N = 39 monitoring stations) for PM 2.5 and PM 10 were around 203 µg.m −3 and 351 µg.m −3 , respectively, while they were 1.97 mg.m −3 , 55.12 µg.m −3 , 29.80 µg.m −3 , 13.04 µg.m −3 , for CO, NO 2 , O 3 and SO 2 . We found a ‘differential’ pollutant behaviour. For example, while both the PMs, CO and NO 2 , frequently exceeded environmental safety thresholds, O 3 and SO 2 always remained below these. For the PMs, CO and NO 2 , we observed three distinct time horizons: (a) pre-Diwali and Diwali (PD&D; 20 October-2 November) with the lowest daily median concentrations ( N = 39 stations); (b) post-Diwali phase I (PDP-I; 2–11 November) with intermediate daily medians and linearly declining over the days and (c) post-Diwali phase II (PDP-II; 12–18 November) recording the highest daily median levels with a polynomial rising trend. Significant (.05 < p <.01) positive associations were found between the daily median PMs, CO and NO 2 concentrations, indicating similar sources. Computations of relative health risks due to excess PM 2.5 levels revealed heightened threats of cardiopulmonary and cancer mortality at all locations. As we reflect on crop stubble burning and the Diwali festival (anthropogenic factor), we observe that winter meteorology (e.g. low wind speed and low solar radiation) plays a decisive role. We point to the current policy shortcomings, especially the graded response action plan, and emphasize the need for socio-technical innovations (crop residue management), institutional reforms, a multistakeholder, participatory action plan and intensifying the existing air quality monitoring programmes.