Hindu - New Delhi
Delhi saw only one ‘Good’ air day this monsoon despite heavy rain: CSE report
Delhi recorded just a single day of ‘Good’ air quality during the entire 92-day monsoon season despite heavy rainfall, according to a new report by the Centre for Science and Environment (CSE).
The report, released on Wednesday (September 30, 2026), noted that the Capital’s ‘Good’ Air Quality Index (AQI) day occurred on July 9, when the combined mean rainfall across the Safdarjung and Palam meteorological stations hit 67.75 mm. The report defied the summer season, as April 1 to May 31 (61 days) and the monsoon as June 1 to August 31 (92 days).
“Out of 92 analysed days, ‘Poor’ days plummeted to just three (3.3 per cent). ‘Satisfactory’ days rose to 35 (38.0 per cent), while ‘Moderate’ days held the single largest share at 53 (57.6 per cent),” the CSE statement noted.
According to the Central Pollution Control Board (CPCB), the AQI scale marks 0–50 as ‘Good’, 51–100 as ‘Satisfactory’, 101–200 as ‘Moderate’, and 201–300 as ‘Poor’.
According to the report, even during the monsoon — when natural atmospheric “washout” and wet deposition effects peak — Delhi’s ambient air quality struggled to sustain clean levels. Despite heavy precipitation, baseline pollution remained elevated, and particulate matter rebounded rapidly within 48 hours of rainfall, it added.
Anumita Roychowdhury, executive director of research and advocacy at CSE, said, “While monsoon rains bring temporary relief, they only mask the underlying crisis. The fact that even heavy rainfall failed to bring consistent ‘Good’ air quality, and that pollution rebounded within 48 hours during dry spells, shows that our baseline emissions remain dangerously high. As we enter winter, we are starting from a baseline where continuous, elevated emissions will inevitably trigger severe seasonal spikes.”
Ms. Roychowdhury added that Delhi cannot rely on nature’s washout in the monsoon or emergency winter bans to manage its air. “What we need is ambitious, year-round, airshed-wide action to permanently cut emissions at their source across all sectors in the NCR,” she said.
Every winter, air pollution spikes drastically across Delhi-NCR and the larger Indo-Gangetic Plains. This seasonal crisis is triggered by meteorological shifts like lower wind speeds and dropping temperatures, and is severely worsened by vehicular emissions, road dust, stubble burning in October and November, and festive firecrackers.
This Day
AI, Data, Fact-Checking Skills Critical for Credible Environmental Reporting
The growing influence of artificial intelligence (AI), data and digital verification tools has made technological competence increasingly critical to credible research, communication and evidence-based decision-making in environment, science and development. MachineLearning & Artificial Intelligence
Against this backdrop, the Centre for Science and Environment (CSE), a leading think tank in the Global South on development, environment and climate change, has announced a Global Online Certificate Course designed to equip professionals with practical skills in AI, data analysis and fact-checking.
The programme is targeted at researchers, academics, communicators, policymakers, development practitioners, government officials, civil society organisations, NGOs and corporate professionals seeking to strengthen their research and communication capacities.
According to CSE, the rapid evolution of AI and digital tools is transforming how professionals research issues, process information, analyse data and communicate complex subjects to diverse audiences.
The organisation said the technologies could be particularly valuable in addressing environmental and developmental challenges, including climate change and biodiversity loss, where large volumes of data increasingly have to be processed and translated into accessible information.
It, however, stressed that the growing availability of AI tools also makes responsible use, verification and fact-checking essential to maintaining professional and institutional credibility.
The certificate course, therefore, seeks to enable participants to use AI responsibly while improving their ability to conduct research, analyse evidence, detect misinformation and produce effective communication materials.
The programme will teach participants how to use AI to streamline research workflows, including data collection, analysis, writing and reporting, while introducing practical approaches to AI-assisted fact-checking and verification. MachineLearning & Artificial Intelligence
Participants will also learn how to apply AI to data visualisation, multimedia content, presentations and public outreach, as well as develop strategies for integrating the technology responsibly into their projects and institutions.
CSE said the programme would be particularly relevant to professionals working in environmental studies, data science, science communication, sustainability, climate action, corporate communication and environmental, social and governance (ESG) activities.
The course is structured as a self-paced online programme comprising video lectures, presentations, tutorials, quizzes and assignments. Participants will also have an opportunity to undertake a project of their choice.
The flexible structure, according to the organisers, is designed to enable participants to complete the programme alongside regular employment or academic commitments.
The six-module programme begins with an introduction to AI, covering its concepts, applications to global challenges and implications. MachineLearning & Artificial Intelligence
The second module focuses on the foundations of science, environment and development communication, including communication barriers and frameworks through which AI tools can be effectively integrated.
The third module examines AI for research, including generating and refining research questions, conducting literature reviews with AI tools and developing effective prompts.
The fourth module focuses on AI and data analysis, with emphasis on analysing and visualising environmental and development data.
Fact-checking and verification form the focus of the fifth module, covering misinformation detection, source validation, image verification and the responsible use of AI in evidence-based communication.
The final module examines AI for effective communication and outreach, including audience-focused communication, multilingual content and prompt design.
CSE said the course was open to researchers and academics, environment and science communicators, policy professionals, development practitioners, government and institutional officers, civil society and NGO personnel, and corporate professionals working in sustainability, ESG and communications.
Participants are required to have access to a computer or laptop and a high-speed internet connection.
The course is being directed by Kiran Pandey, Programme Director, Information Management, CSE, while Susan Chacko, Manager, Information Management, CSE, is the course coordinator.
Urban Acres
Delhi Air Pollution Rises Again After Rain, Exposing a Year-Round Crisis
Delhi’s monsoon offered only brief relief from air pollution, with the city’s average PM2.5 concentration rising sharply after rainfall stopped. A Centre for Science and Environment assessment found that Delhi recorded just one day of “good” air quality across the 92 days from June to August, while PM2.5 levels rose 37.9% within 48 hours of rain events.
The findings challenge the assumption that heavy rainfall can substantially resolve Delhi’s air pollution problem. The city received 576.9 mm of rain during the monsoon period, but the improvement in air quality was temporary. Rain removed some particulate pollution from the atmosphere, yet gaseous pollutants remained, allowing pollution levels to rebound soon after the weather cleared.
That distinction matters because Delhi’s air quality problem is not limited to the winter months. The CSE assessment shows that the city experienced pollution across the monsoon, although at lower average levels than during summer. Delhi’s average PM2.5 concentration during the monsoon was 40.2 micrograms per cubic metre, 33.2% lower than the summer average of 60.2 micrograms per cubic metre. Lower pollution, however, did not translate into consistently clean air.
Of the 92 monsoon days analysed, 53, or 57.6%, fell in the “moderate” air quality category. Another 35 days were classified as “satisfactory”, three as “poor” and only one as “good”. The single good-air day was recorded on 9 July, when 67.75 mm of rain fell. On 8 August, Delhi received the season’s highest rainfall of 101.05 mm, but air quality reached only the “satisfactory” category.
The pattern indicates that rainfall can temporarily suppress particulate matter without removing the emissions that continuously enter the urban atmosphere. In its analysis of six separate rainfall events, CSE found that the average PM2.5 level stood at 40.6 micrograms per cubic metre before rain. It fell to 32.7 during rainfall, a reduction of 19.5%.
The improvement began to reverse almost immediately. PM2.5 rose to 36.2 micrograms per cubic metre 24 hours after rainfall and reached 45.1 micrograms per cubic metre after 48 hours. The level two days after rain was therefore 37.9% higher than during the rainfall event and 11.1% higher than the pre-rain average.
This rebound is the central evidence in the assessment. Rainfall changes atmospheric conditions for a short period, but it does not address the sources producing pollution on the ground. Once rainfall ends, emissions from transport, industry, waste burning, construction-related activity and other urban sources continue to enter the air. The data supplied by CSE does not assign a precise share of the post-rain increase to each source, but it demonstrates that weather-driven improvement is not equivalent to emissions reduction.
The pollutant mix also complicates the idea that rain alone can deliver clean air. CSE found that ground-level ozone was the dominant pollutant on 20 monsoon days. Nitrogen dioxide and carbon monoxide were also significant. While rain can wash particulate pollutants out of the air, gaseous pollutants can persist, allowing air quality to deteriorate even during a season associated with frequent showers.
This is an important governance distinction. A city can record a visible and measurable fall in PM2.5 during rain without having improved its underlying emissions profile. If pollution returns within one or two days, the immediate atmospheric benefit has not been matched by a change in the systems that generate emissions. The result is a cycle in which residents receive intermittent relief but remain exposed to pollution for much of the year.
The findings also place Delhi’s winter pollution debate in a wider annual context. CSE’s executive director for research and advocacy, Anumita Roychowdhury, said rainfall provides temporary relief but does not eliminate the root sources of pollution. She called for year-round emission reduction across the National Capital Region rather than reliance on temporary measures during winter.
That recommendation points to the institutional challenge created by Delhi’s air basin. Pollution does not stop at municipal or state boundaries, and the assessment specifically calls for an integrated “airshed” approach across the NCR. Such an approach would require authorities to treat the region’s air as a shared environmental system rather than as a problem belonging to Delhi alone.
The policy measures cited by CSE cover several urban systems. These include an electricity-based transport system, cleaner industrial fuels, a ban on open waste burning, recycling of construction waste, uninterrupted electricity supply and integrated air-quality management across the NCR. Together, they show that air pollution is connected to mobility, industrial production, waste management, construction and power reliability.
Each of these areas is administered through different institutions and enforcement arrangements. Transport policy involves public agencies, vehicle operators and commuters. Industrial fuel decisions involve factories, regulators and energy suppliers. Waste burning is linked to collection, disposal and enforcement by local authorities. Construction-waste recycling depends on the capacity to collect and process material. Reliable electricity can reduce dependence on polluting backup systems. An airshed strategy would have to coordinate these responsibilities across jurisdictions.
The monsoon data also exposes the limits of using seasonal averages as the sole measure of progress. Delhi’s average PM2.5 level was substantially lower during the monsoon than in summer, but the city still had only one good-air day. The average therefore captures an overall reduction while obscuring the frequency with which residents experienced air that remained moderate or worse.
The six rainfall events provide a more dynamic picture. They show how quickly air quality changes before, during and after rain. A decline from 40.6 to 32.7 micrograms per cubic metre may appear significant while the rain is falling, but the subsequent rise to 45.1 within 48 hours shows that the improvement was not durable. For urban policy, duration matters as much as the size of a temporary decline.
The evidence also raises a question about how authorities define success. If clean-air conditions appear only during exceptional weather and disappear soon afterwards, weather is doing more of the work than policy. A durable improvement would require pollution levels to remain lower after atmospheric conditions return to normal. The assessment does not establish that such a shift has occurred in Delhi.
For residents, the implications are practical. The end of a rainfall spell cannot be treated as the end of an air-pollution episode. People may experience visibly clearer conditions during rain, followed by a rapid return of fine particulate pollution and continued exposure to ozone, nitrogen dioxide and carbon monoxide. The city’s daily experience of air quality is therefore shaped by both weather and the performance of urban systems.
What the CSE assessment confirms is that Delhi’s monsoon pollution is not a contradiction but a structural signal. Rain can lower PM2.5 temporarily, yet the city’s emissions sources remain active. What remains unresolved is how quickly and effectively institutions across the NCR can reduce those emissions throughout the year. The next test is whether the measures identified by CSE are implemented as coordinated systems rather than activated only when winter pollution becomes an emergency.
