• Urban Lab

Mega cities in India see high concentration of ozone pollution this summer

All mega cities in India, including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai, saw high concentration of ground-level ozone pollution this summer season, according to a new analysis by think tank Centre for Science and Environment (CSE). A previous analysis had shown that ozone, instead of particulate matter, was the main pollutant in Delhi's daily Air Quality Index (AQI) on several days this summer. The new analysis by the CSE's Urban Lab highlighted that ozone, unlike primary pollutants, is not released directly from any source.

• Urban Lab

Mega cities in India see high concentration of ozone pollution this summer

A recent analysis by the Centre for Science and Environment (CSE) reveals high ground-level ozone pollution in major Indian cities like Kolkata, Bengaluru, Mumbai, Hyderabad, and Chennai this summer. Ozone, formed by reactions involving pollutants from vehicles and industries, poses a public health risk. The analysis emphasizes the need for improved monitoring and mitigation strategies to address this growing concern.

• Urban Lab

Ozone pollution: Mega Indian cities see high concentration this summer

All mega cities in India, including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai, saw high concentration of ground-level ozone pollution this summer season, according to a new analysis by think tank Centre for Science and Environment (CSE). A previous analysis had shown that ozone, instead of particulate matter, was the main pollutant in Delhi's daily Air Quality Index (AQI) on several days this summer. The new analysis by the CSE's Urban Lab highlighted that ozone, unlike primary pollutants, is not released directly from any source. It forms through complex chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO), pollutants emitted by vehicles, power plants, industries and other sources of combustion. These substances react in the presence of sunlight, leading to the formation of ozone at the ground level. Anumita Roychowdhury, executive director at the CSE, said: "If unchecked, this can become a serious public health crisis as ozone is a highly-reactive gas and can be harmful even with short-duration exposures." She added that while cities in north India experience high ozone levels in summer due to intense heat and strong sunlight, cities in warmer climates are also seeing consistent ozone exceedance in other seasons. The current policy focus must be expanded to include improved monitoring, the mitigation of this toxic gas and a reduction in high local exposures. Ozone mitigation needs drastic control over a range of gases from vehicles, industry and all combustion sources, Roychowdhury said. Sharanjeet Kaur, deputy programme manager at the CSE's Urban Lab, said: "Inadequate monitoring, limited data and inadequate methods of trend analysis have weakened the understanding of this growing public health hazard across cities of India. Instead of merely averaging out the levels for the city, which is the standard practice to estimate the AQI, it is also important to adequately capture the high levels of local build-up and exposures in the hotspots and design mitigation strategies accordingly." Between March 1 and May 31 this year, Mumbai recorded ozone exceedance on 32 out of 92 days across its monitoring stations, a 42-per cent drop compared to the same period last year. The worst day in terms of spread was March 29, when eight out of 31 stations reported exceedance. The highest ground-level ozone concentration recorded was 90 micrograms per cubic metre. In Kolkata, ozone levels crossed the safe limit on 22 out of 92 days, a 45-per cent decline compared to last summer. The city also saw an overall improvement, with the average hourly ozone peak dropping by 22 per cent. Bengaluru saw ozone exceedance on 45 of the 92 days, a 29-per cent increase from last year. The worst day was March 31, when four of 14 stations recorded levels above the standard.

• Urban Lab

Ozone pollution surges across major Indian cities, posing serious health risks: CSE

Centre for Science and Environment (CSE) ... Centre for Science and Environment (CSE). Revealing a disturbing trend, the latest analysis by the

• Urban Lab

High ozone pollution observed in Indian mega cities

Ground-level ozone pollution jumped in big Indian cities like Kolkata, Bengaluru, Mumbai, Hyderabad, and Chennai this summer, says a new Centre for Science and Environment (CSE) report. The main culprits? Sunlight mixing with emissions from cars, power plants, and factories. Ozone is a serious lung irritant Ozone isn't just a buzzword—it's a gas that can seriously mess with your lungs even after short exposure. Northern cities see sharp spikes when the heat is on; warmer metros deal with high ozone levels most of the year. Experts are urging better local tracking and tougher emission rules to help keep people safe. Bengaluru, Chennai, and Hyderabad had varying experiences Between March and May 2025, Mumbai and Kolkata actually saw about 40-45% fewer days with high ozone compared to last year. Hyderabad did even better with a 55% drop. But Bengaluru had a 29% increase in bad ozone days, while Chennai went from zero last year to 15 this time around. Clearly, each city needs its own game plan to tackle the problem.

• Urban Lab

Summer of Ozone: India's Cities Battle Rising Air Pollution

India's mega cities, such as Kolkata, Bengaluru, Mumbai, Hyderabad, and Chennai, are grappling with high levels of ground-level ozone pollution this summer, according to new findings by the Centre for Science and Environment (CSE). The organization emphasized that if not curtailed, this pollution could grow into a significant public health concern. The research uncovered that ozone, unlike primary pollutants, is a secondary pollutant forming through intricate chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide (CO). These emissions, sourced from vehicles, power plants, and other combustion processes, react in the presence of sunlight to create ozone at Earth's surface. Anumita Roychowdhury, CSE's Executive Director, expressed concern over escalating ozone levels, particularly in north Indian cities in summers, due to intense heat. Highlighting a gap in adequate monitoring and mitigation strategy, experts call for expanded policy focus and better data analysis to manage the crisis effectively.

• Urban Lab

कोलकाता, बेंगलुरु, मुंबई... भारत के इन शहरों के लिए मुसीबत ला रहा OZONE प्रदूषण!

भारत के बड़े शहरों जैसे कोलकाता, बेंगलुरु, मुंबई, हैदराबाद और चेन्नई में इस गर्मी (2025) में जमीन के स्तर पर ओजोन प्रदूषण ने खूब सिर उठाया है. सेंटर साइंस एंड एनवायरनमेंट (CSE) की नई रिपोर्ट के मुताबिक,

• Industrial Pollution

India is at the Energy Crossroads and Must Clean Up its Coal Act

India’s complicated love affair with coal is no secret. As the world’s third-largest carbon emitter, the country is under immense pressure—both domestic and global—to reduce its carbon footprint. Yet coal remains the cornerstone of India’s energy matrix, powering over 70% of its electricity generation. The question isn’t whether India can wish away coal—it’s how it can make coal cleaner while pursuing economic growth and energy security. At a recent event hosted by the Centre for Science and Environment, Ashok Lavasa, a former secretary to key union ministries, captured this nuance aptly: “If coal is king, can it be a benevolent king?” The answer lies not in utopian ideals but in pragmatic solutions that blend energy reliability with environmental responsibility. Coal’s Staying Power—and Its Environmental Cost Electricity demand in India is soaring. From 2021 to 2025 alone, it jumped by over 9%, with forecasts suggesting it could double by 2030. Renewable energy is growing too—currently making up 46% of installed capacity—but its intermittency limits its ability to meet peak demand, especially at night. Thermal power plants offer grid stability and continuous supply, but at a steep environmental cost. More than 40% of India’s annual carbon emissions stem from electricity generation, with coal being the main culprit. While the net-zero target by 2070 remains firm, the route to get there is complicated. Can We Burn Coal Without Burning the Planet? The answer may not lie in phasing out coal entirely, but in innovating how it’s used. A recent CSE report suggests decarbonising thermal plants could slash emissions by up to 30%. One proposal includes reducing the minimum operational threshold of these plants from 55%—a level often maintained even when renewable power is available—to lower figures, enabling more dynamic balancing with green sources. Another option is to increase the use of agricultural residue in place of coal. This has already led to measurable reductions in Delhi and surrounding areas, though adoption elsewhere remains minimal. Technologies that capture carbon dioxide emissions are also being explored but currently capture only about 0.1% of global emissions. The path to cleaner coal, however, is paved with costs and uncertainties. Upgrading existing infrastructure, adopting new technology, and training operators require substantial capital and policy commitment. And the million-dollar question remains—who pays for all this? Policy Steps Forward—or a Step Backward? In a controversial move, India recently exempted 78% of its thermal power plants from installing flue gas desulphurisation (FGD) systems, which are vital for controlling sulphur dioxide (SO₂) emissions. These emissions contribute to fine particulate matter, which causes respiratory and cardiovascular diseases. The Ministry’s rationale is based on low current SO₂ levels and the assumption that Indian coal has lower sulphur content. Experts argue otherwise. Studies show that thermal plants can impact air quality up to 200 kilometers away, and simply using taller chimneys disperses pollutants without eliminating them. With just 8% of plants having installed FGD units so far, this rollback of environmental safeguards could affect millions. A Glimmer of Strategic Innovation There is a silver lining. The government is exploring the conversion of 10 retired thermal power plants into nuclear power stations. These sites already have much of the necessary infrastructure and offer a low-carbon pathway to help meet India’s goal of 100 GW nuclear capacity by 2047. If implemented carefully—keeping in mind seismic stability, water access, and population proximity—this could be a transformative step. India’s journey toward a cleaner energy future is not a linear one. Coal will remain part of the equation for decades to come. But it’s what India does in the meantime—how it makes coal cleaner, invests in energy storage, balances grid stability, and builds trust with its people and the planet—that will define its leadership in the energy transition. The king isn’t going anywhere just yet. But with the right reforms, it just might learn to rule with a lighter, greener touch.

• Climate Change and Green Economy

India crosses 50% non-fossil power capacity target under Paris Agreement: Cabinet

“As a commitment made to the Paris Agreement, the achievement of India’s NDC target is commendable and signals its intent to diversify its energy mix whilst continuing to tackle growing power demand. Having achieved this, all efforts must now be directed to raise the actual share of generation from renewables (combined with storage) in the power mix—which currently stands at 13% for solar and wind—to displace coal,” programme manager for climate change at the Centre for Science and Environment, Avantika Goswami, said. India has surpassed its target of installing 50% of its power capacity from non-fossil fuel sources, achieving a key nationally determined contribution (NDC) under the Paris Agreement five years ahead of the 2030 target, the Union Cabinet said on Wednesday. “India’s achievement of 50% non-fossil fuel installed capacity ahead of the target year is a testament to its ambition, innovation, and commitment to sustainable development. It affirms that development and decarbonisation are not contradictory goals, but can in fact reinforce each other. As the country moves toward the goal of 500 GW of non-fossil capacity by 2030 and net-zero emissions by 2070, the path forward must be bold, inclusive, and technology-driven,” union minister of new and renewable energy Pralhad Joshi said on July 14. India’s updated NDCs under the Paris Agreement, submitted in August 2022, said that the country aims to reduce the emissions intensity of its gross domestic product (GDP) by 45% by 2030 from 2005 levels; increase the share of non-fossil fuel-based energy resources to 50% of its installed power generation capacity by 2030; and create an additional carbon sink of 2.5 to 3 billion tonnes of CO2 equivalent through additional forest and tree cover by 2030. According to data from the ministry of new and renewable energy, India’s total power capacity as of June 30 was 484.8 GW, with 242.04 GW (49.92%) from thermal/coal, 8.78 GW (1.81%) from nuclear, and 234.00 GW (48.27%) from renewable sources, including large hydro. The cabinet also said that India is on track to fulfil its commitments under the 2021 United Nations Climate Change Conference (COP26), held in Glasgow. Addressing a gathering that included over 120 heads of state at COP26, Prime Minister Narendra Modi had said India would increase its non-fossil fuel energy capacity to 500 GW by 2030, fulfil 50% of its energy requirements from renewable sources by 2030, reduce its total projected carbon emissions by 1 billion tonnes between now and 2030, reduce the carbon intensity of its economy by 45% by 2030, and achieve net-zero emissions by 2070. “As a commitment made to the Paris Agreement, the achievement of India’s NDC target is commendable and signals its intent to diversify its energy mix whilst continuing to tackle growing power demand. Having achieved this, all efforts must now be directed to raise the actual share of generation from renewables (combined with storage) in the power mix—which currently stands at 13% for solar and wind—to displace coal,” programme manager for climate change at the Centre for Science and Environment, Avantika Goswami, said. The cabinet committee on economic affairs, chaired by PM Modi, has granted enhanced delegation of powers to the National Thermal Power Corporation (NTPC) Limited, beyond the existing guidelines for Maharatna central public sector enterprises (CPSEs). This will allow NTPC to invest in its subsidiary, NTPC Green Energy Limited (NGEL), and enable NGEL to further invest in NTPC Renewable Energy Limited (NREL) and its other joint ventures and subsidiaries. The investment limit was raised from the earlier approved ₹7,500 crore to up to ₹20,000 crore for renewable energy capacity addition, in line with the goal of achieving 60 GW of renewable energy capacity by 2032.

• Urban Lab

Hyderabad’s Bolarum saw highest ozone pollution this summer, says study

Ozone pollution spiked in several parts of Hyderabad this summer, but it was the industrial belt of Bolarum that saw the worst of it. Between March 1 and May 31, Bolarum recorded 17 days when ground-level ozone levels breached the safe limit — the highest in the city — according to a research paper published by the Centre for Science and Environment titled ‘An invisible threat: Ground-level ozone – Metro cities’ based on a study by Anumita Roychowdhury and Sharanjeet Kaur. The study tracked air quality in five major cities — Hyderabad, Mumbai, Kolkata-Howrah, Bengaluru and Chennai — using data from 80 stations under the Continuous Ambient Air Quality Monitoring System (CAAQMS). As per the study, Bolarum is most chronically affected by ground-level ozone pollution, and exceeded the standard for 17 days in the study period. While the standard is 100 μg/m³ (micrograms per cubic metre of air), the levels of ozone nearly touched 140 μg/m³ on the days mentioned. There were no exceedances at other stations in the city barring ICRISAT which exceeded the standard for two days and Ramachandrapuram which exceeded for one day, totalling to 20 days of ozone exceedance in the city. The days of exceedance in Hyderabad were more concentrated between May 2 and 20. Good news is that the figure is 55% lower than what was recorded last summer. A comparison of May 2025 with May 2024 reveals that ground-level ozone is now lingering in the atmosphere even after sunset, and the average hourly ozone peak is 3% higher than last year, the study noted. At 45, Bengaluru recorded the highest number of days with ozone exceedance. Mumbai recorded 32 days, Kolkata 22 days, and Chennai recorded the lowest at 15 days. Unlike primary pollutants which are emitted directly from sources such as vehicles and industries, ground level ozone is formed through intricate chemical reactions involving nitrogen oxides, volatile organic compounds (VOCs) and carbon monoxide, which are the pollutants released by vehicles, power plants, factories and other combustion sources, the study said. In the presence of sunlight, these substances undergo a series of cyclic reactions that result in the ozone formation near the ground. VOCs also have natural sources such as vegetation adding to the complexity, which explains the higher levels at ICRISAT. What’s more threatening is that the ground level ozone can travel long distances, turning into a regional pollutant. It impacts agricultural productivity, threatening food security. Ozone is a highly reactive gas which can be harmful even with short duration exposure, and result in serious public health crisis, the study warned. Ground level ozone can inflame and damage the airways, increase susceptibility to infections and worsen respiratory conditions such as asthma, chronic bronchitis and emphysema. Children with underdeveloped lungs, order adults and people with existing respiratory conditions are particularly vulnerable. Hyderabad is prone to experience ozone exceedances during winter too, driven by cold, stagnant conditions and poor vertical mixing. But this winter, there was substantial improvement, with the city recording just nine days of exceedance which is a sharp decline from 43 days recorded during the winter of 2024, the study observed.

• Urban Lab

भारत के इन बड़े शहरों में ओजोन प्रदूषण बना मुसीबत, CSE की नई रिपोर्ट में आया सामने

इस गर्मी के मौसम में कोलकाता, बेंगलुरु, मुंबई, हैदराबाद और चेन्नई सहित भारत के सभी महानगरों में सतह के नजदीक ओजोन प्रदूषण की उच्च सांद्रता देखी गई। यह दावा थिंक टैंक सेंटर फॉर साइंस एंड एनवायरनमेंट (सीएसई) ने अपने नए विश्लेषण के आधार पर किया है। सीएसई के पूर्व के विश्लेषण से पता चला था कि इस गर्मी में कई दिनों तक दिल्ली के दैनिक वायु गुणवत्ता सूचकांक (एक्यूआई) में ठोस कणों के बजाय ओजोन मुख्य प्रदूषक था। सीएसई की शहरी प्रयोगशाला द्वारा किए गए नए विश्लेषण में खुलासा हुआ है कि प्राथमिक प्रदूषकों के विपरीत ओजोन किसी भी स्रोत से सीधे उत्सर्जित नहीं होता है। यह नाइट्रोजन ऑक्साइड (एनओएक्स), वाष्पशील कार्बनिक यौगिक (वीओसी) और कार्बन मोनोऑक्साइड (सीओ), वाहनों, बिजली संयंत्रों, उद्योगों और दहन के अन्य स्रोतों द्वारा उत्सर्जित प्रदूषकों से जुड़ी जटिल रासायनिक प्रतिक्रियाओं के माध्यम से बनता है। ये पदार्थ सूर्य के प्रकाश की उपस्थिति में प्रतिक्रिया करते हैं, जिससे सतह के नजदीक ओजोन का निर्माण होता है। सीएसई की कार्यकारी निदेशक अनुमिता रॉयचौधरी ने कहा, ‘यदि इस पर नियंत्रण नहीं किया गया तो यह एक गंभीर जन स्वास्थ्य संकट बन सकता है, क्योंकि ओजोन एक अत्यधिक प्रतिक्रियाशील गैस है और कम समय तक भी संपर्क में आने पर हानिकारक हो सकती है।’ उन्होंने कहा कि जहां उत्तर भारत के शहरों में गर्मियों में तीव्र गर्मी और तेज धूप के कारण ओजोन का स्तर अधिक रहता है, वहीं गर्म जलवायु वाले शहरों में भी अन्य मौसमों में ओजोन का स्तर लगातार बढ़ रहा है। रॉयचौधरी ने कहा कि वर्तमान नीति का विस्तार किया जाना चाहिए जिसमें बेहतर निगरानी, इस जहरीली गैस का शमन और उच्च स्थानीय जोखिम में कमी को शामिल करना शामिल हो। रॉयचौधरी ने कहा कि सतह के नजदीक ओजोन के स्तर को कम करने के लिए वाहनों, उद्योगों और सभी दहन स्रोतों से निकलने वाली गैसों पर कठोर नियंत्रण की आवश्यकता है। विश्लेषण के मुताबिक इस साल एक मार्च से 31 मई के बीच, मुंबई के निगरानी केंद्रों में 92 में से 32 दिनों में ओजोन का स्तर ज्यादा दर्ज किया गया, जो पिछले साल की इसी अवधि की तुलना में 42 प्रतिशत कम है। प्रसार के लिहाज से सबसे खराब दिन 29 मार्च था, जब 31 में से आठ केंद्रों से ओजोन के स्तर के ज्यादा होने की सूचना मिली। स्तह के नजदीक ओजोन की अधिकतम सांद्रता 90 माइक्रोग्राम प्रति घन मीटर दर्ज की गई। कोलकाता में, 92 में से 22 दिनों में ओजोन का स्तर सुरक्षित सीमा को पार कर गया। बेंगलुरु में 92 दिनों में से 45 दिनों में ओजोन का स्तर मानक से ज्यादा दर्ज किया गया जो पिछले साल की तुलना में 29 प्रतिशत अधिक है। सबसे बुरा दिन 31 मार्च का था, जब 14 में से चार केंद्रों पर ओज़ोन का स्तर मानक से ज़्यादा दर्ज किया गया। हैदराबाद में 20 दिन ऐसे रहे जब सतही ओजोन का स्तर अधिक था। शहर में ओज़ोन का उच्चतम स्तर 51 माइक्रोग्राम प्रति घन मीटर दर्ज किया गया। इसी प्रकार इस साल गर्मी में चेन्नई में 15 दिन ऐसे थे जब ओजोन प्रमुख प्रदूषक था जबकि पिछले साल एक दिन भी इस श्रेणी में दर्ज नहीं किया गया था।

• Urban Lab

Indian mega cities face high ozone pollution this summer: CSE

Every leading metropolis and mega city in India – including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai – has been struck by high ozone levels in the summer of 2025. Ground-level ozone pollution has spiked and concentrations have exceeded the eight-hour standards on a number of days. This has emerged from an analysis done by Centre for Science and Environment. The analysis has been done by the Urban Lab in CSE under its ‘air quality tracker’ initiative. The assessment highlights that unlike primary pollutants, ozone is not emitted directly from any source. It forms through intricate chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide (CO) — pollutants that are released by vehicles, power plants, factories and other combustion sources. In the presence of sunlight, these substances undergo a series of cyclic reactions that result in the formation of ozone at ground level. VOCs also have natural sources such as vegetation, adding to the complexity. Ground-level ozone accumulates not only in urban environments but can also travel long distances, turning into a regional pollutant. It can impact agricultural productivity and threaten food security. Given ozone’s highly reactive nature, the ambient air quality standards for it are set for eight-hour averages, instead of 24-hour averages. Anumita Roychowdhury, executive director, CSE, says: “If unchecked, this can become a serious public health crisis as ozone is a highly reactive gas and can be harmful even with short-duration exposures. In contrast to cities in north India where high summer temperatures and intense solar radiation can lead to ozone levels exceeding the standards, other cities in warm climates are experiencing consistent ozone exceedance during other seasons as well.” Roychowdhury adds: “The current policy focus must be expanded to include improved monitoring and mitigation of this toxic gas and reduction in high local exposures. Ozone mitigation needs drastic control over a range of gases from vehicles, industry and all combustion sources.” “Inadequate monitoring, limited data and inadequate methods of trend analysis have weakened the understanding of this growing public health hazard across cities of India. Instead of merely averaging out the levels for the city – which is the standard practice to estimate AQI — it is also important to capture adequately the high levels of local build-up and exposures in the hotspots and to design mitigation strategies accordingly ,” says Sharanjeet Kaur, deputy programme manager at the Urban Lab in CSE. The CSE review shows that exposure to ground-level ozone can inflame and damage the airways, increase susceptibility to infections, and worsen respiratory conditions such as asthma, chronic bronchitis and emphysema. Children with underdeveloped lungs, older adults, and individuals with existing respiratory conditions are particularly vulnerable. Ozone exposure increases the frequency and severity of asthma attacks, often leading to higher rates of hospitalisation. The investigation method: This assessment has traced trends during summer (March-May) between 2022 and 2025 (up to May 31). It is based on publicly available granular real time data (15-minute averages) from the Central Pollution Control Board’s official online portal – the Central Control Room for Air Quality Management. The data has been captured from 80 official stations under the Continuous Ambient Air Quality Monitoring System (CAAQMS), spread across Mumbai (31), Kolkata-Howrah (12), Bengaluru (14), Hyderabad (14) and Chennai (nine). Says Kaur: “Given the volatile and highly localised nature of ground-level ozone pollution build-up and its variability across space, and consistent with the global good practice, this analysis has considered station-level trends in terms of number of days exceeding the eight-hour standard over time.” She points out that as ozone formation depends on complex atmospheric chemistry and on photochemical reactions, its level varies across the time and space horizon. Meteorological parameters such as sunny and warm weather, stagnant wind patterns etc have a bearing on its formation. Kaur says: “This analysis tracks exceedances at each station in metro cities — breach of the standard by even one station is considered exceedance by the metro city in which the station is located. Days with multiple stations exceeding the standard indicates the severity of the spatial spread and number of people exposed.” The study has considered global good practice and taken on board the USEPA approach of computing eight-hour averages for a day and then checking for the maximum value among them to capture the daily ozone pollution level. USEPA assesses city-wide or regional AQI based on the highest value recorded among all stations of the city or the region. Thus, trends have been calculated in terms of number of days when the daily level has exceeded the eight-hour standard (referred as exceedance days hereafter). City-wise highlights Mumbai Summer trends: Between March 1 and May 31 this summer, Mumbai recorded ozone exceedance on 32 out of 92 days across its air quality monitoring stations. This marks a 42 per cent decline compared to the same period last year. The worst day in terms of spatial spread was March 29, when eight out of 31 monitoring stations reported exceedance. The highest regional ground-level ozone concentration reached was 90 µg/m³. Ozone hotspots: Chakala is the most chronically affected area in Mumbai. It exceeded the standard for 29 days between March and May. It is followed by Byculla and Kherwadi. Locational variations and relationship with other pollutants: The spatial distribution of ground-level ozone generally shows an inverse relationship with nitrogen dioxide. In areas with high NO ₂ concentrations, particularly near traffic-dense corridors, ozone formation is typically suppressed as ozone reacts with nitric oxide (NO) and breaks down to dissipate. Chakala consistently reports higher concentrations of both NO ₂ and ozone. Such localised variations underscore the complex interplay between precursor pollutants, meteorological conditions and emission sources that shape ozone behavior across different parts of the city. A comparison of May 2025 with May 2024 reveals that ground-level ozone is now persisting longer into the evening, even after sunset. However, the average hourly ozone peak this summer is 35 per cent lower than last year, indicating possible changes in atmospheric chemistry or precursor emissions. Daily trends show that when NO ₂ levels increase during morning and evening hours, it helps neutralise the ozone concentration and dissipate it. But ozone levels rise during off-peak hours when NO 2 levels are comparatively lower. Ozone build-up during other seasons: Unlike most northern cities, Mumbai records higher ground-level ozone concentrations during winter months during December – February. During the winter of 2024-25, the city experienced 87 days of ozone exceedance—a 10 per cent rise from the previous winter’s exceedance of 78 days. The atmospheric conditions, photochemical reactions and emissions levels would have contributed to this trend. Kolkata Summer trends: About 22 out of 92 days this summer (between 1 March and 31 May) have registered exceedance of ozone standards, as per the air quality monitoring stations of Kolkata. This marks a 45 per cent decline compared to previous summer. Kolkata has seen an overall improvement, with the average hourly ozone peak declining by 22 per cent this summer. Ozone hotspots: Rabindra Sarobar and Jadavpur have seen more days exceeding the standards compared to other locations. Locational variations and relationship with other pollutants: The spatial distribution of ground-level ozone generally shows an inverse relationship with nitrogen dioxide . In areas with high NO ₂ concentrations particularly near traffic-dense corridors, ozone formation is typically suppressed where ozone reacts with nitric oxide to break down and dissipate. It usually drifts and builds up in areas with less pollution. Ozone build-up during other seasons: While ozone pollution is typically associated with the summer months with strong sun in northern India, Kolkata has consistently recorded elevated ground-level ozone concentrations during the winter (November to February) and pre-monsoon seasons as well. The atmospheric conditions, relatively warmer climate, photochemical reactions and emissions levels would have contributed to this trend. During the winter of 2024-25, Kolkata experienced 28 days of ozone exceedance, marking a 7 per cent decline from the 30 days recorded in the previous winter. In the twin city of Howrah, 58 out of 92 days this summer (between 1 March and 31 May) have registered exceedance among its air quality monitoring stations. Dasnagar in Howrah has shown the maximum exceedance. During winter, Howrah has witnessed 81 days of ozone exceedance – increasing from 14 days the previous year. Bengaluru: Summer trends: Forty-five out of 92 days this summer (between 1 March and 31 May) have registered exceedance of ozone standards as per the data available from the air quality monitoring stations of Bengaluru. This marks a 29 per cent increase compared to last summer. The worst day in terms of spatial spread was March 31, when four out of 14 monitoring stations reported exceedance. Ozone hotspots: Hombegowda Nagar has seen the maximum exceedance. It exceeded the standard for 31 days this March-May. It is followed by Bapuji Nagar . Locational variations and relationship with other pollutants: A comparison of May 2025 with May 2024 shows a 28 per cent decline in average hourly ozone peaks — ozone is no longer persisting in the atmosphere after sunset, as was observed last year. Daily trends show that when NO ₂ levels increase during morning and evening hours, it helps neutralise the ozone concentration and dissipate it. But ozone levels rise during off-peak hours when NO 2 levels are comparatively lower. Ozone build-up during other seasons: In Bengaluru, ozone formation occurs in both winter and summer. However, this year’s data reveals a significant shift of ozone concentrations to the spring season (February to April): a 31 per cent increase is visible, compared to the same period last year. This points to a growing trend of early-season ozone formation, driven by warmer temperatures, intensified solar radiation, and possibly changing precursor emission patterns. Hyderabad Summer trends: There have been 20 days this summer (between 1 March and 31 May) that have registered exceedance among the air quality monitoring stations of Hyderabad. This marks a 55 per cent decline compared to last summer . The highest regional intensity was 51 µg/m³. Ozone hotspots: Bollaram is most chronically affected by ground-level ozone pollution. It exceeded the standard for 17 days this March-May. There have been no exceedances at other stations in the city barring ICRISAT (exceeding the standard for two days) and Ramachandrapuram (one day). Locational variations and relationship with other pollutants: A comparison of May 2025 with May 2024 reveals that ground-level ozone is now lingering in the atmosphere even after sunset, and the average hourly ozone peak is 3 per cent higher than last year. Ozone build-up during other seasons: Hyderabad frequently experiences wintertime ozone exceedances, driven by cold, stagnant conditions and poor vertical mixing. Urban traffic and industrial emissions, when combined with low dispersion, lead to ozone accumulation even under weaker winter sun. However, this winter season (December to January), the city witnessed a substantial improvement, recording just nine days of ozone exceedance, a sharp decline from 43 days during the previous winter. Chennai Summer trends: About 15 out of 92 days this summer (between 1 March and 31 May) have registered exceedance as per the data available from the air quality monitoring stations of Chennai. However, no exceedance was reported during the same period last year. In comparison, the summer of 2023 saw three exceedance days, while 2022 recorded 19. The highest regional intensity this summer was 64 µg/m³. Ozone hotspots: Alandur is most chronically affected by ground-level ozone pollution. It exceeded the standard for 15 days this March-May. There have been no exceedances at other stations in the city. Locational variations and relationship with other pollutants: Data from May 2025 reveals that ground-level ozone is now lingering in the atmosphere well after sunset, and the average hourly ozone peak has surged by 76 per cent compared to May 2024. Ozone build-up during other seasons : Chennai typically experiences rising ozone levels in the early summer months, when drier air, clear skies and reduced wind speeds delay pollutant dispersion. This allows for increased photochemical activity, especially during bright, sunny days with minimal atmospheric mixing. This summer (March to May 2025), Chennai recorded 15 days of ozone exceedance, marking a significant shift from zero exceedance days during the same period last year. Additionally, during the winter months (December–February), the number of ozone exceedance days has also risen from seven days last year to 10 days this winter. The way forward: Ground-level ozone is beginning to emerge as a pollutant of concern with cities experiencing days exceeding the eight-hour standards. While the level of exceedance is expected to be higher during the summer months with strong sun-shine days and heat, this is emerging as a round the year problem in the warmer climate. Says Roychowdhury: “Clean air action plan for cities and the states need to address this multi-pollutant challenge urgently. It is important to learn from the advanced economies that after controlling particulate pollution have fallen into the grip of rising NOx and ozone crisis. It is important to prevent this trap.” Clean air action plan for the city needs to integrate ozone mitigation to implement stringent measures to upscale zero emissions vehicles, clean industrial processes and fuels, eliminate waste burning with hundred percent remediation of legacy waste, collection, segregation and material recovery, and replace solid fuels with clean fuels in households. Integrate ozone in the Graded Response Action Plan to take emergency action to target the emitter of precursor gases like vehicles and industry that form ozone and to reduce short term exposures. Develop regional action plan on ozone : Ground-level ozone gets created in polluted areas but drifts and accumulates in cleaner urban environments, urban peripheries and surrounding rural areas affecting agricultural productivity and food security. While in polluted areas ozone further reacts with pollutants to dissipate, in cleaner environment it lives longer. Ozone is thus a regional pollutant that requires effective control at both local and regional level.

• Urban Lab

Ozone Pollution: भारत के इन शहरों के लिए खतरा बन रहा 'ओजोन' प्रदूषण, जानिए आखिर ये क्या होता है

वर्तमान समय में भारत के बड़े शहर प्रदूषण की मार झेल रहे हैं। अब इस बीच एक रिपोर्ट सामने आई है, जो हैरान करने वाली है। एक नई रिपोर्ट में जानकारी सामने आई है कि भारत के बड़े शहरों जैसे कोलकाता, बेंगलुरु, मुंबई, हैदराबाद और चेन्नई में इस साल गर्मी के दौरान जमीन के स्तर पर ओजोन प्रदूषण काफी बढ़ा हुआ था। सेंटर फॉर साइंस एंड एनवायरनमेंट (CSE) की नई रिपोर्ट में कहा गया है कि शहरों में ओजोन का स्तर कई दिनों तक आठ घंटे के मानक से अधिक रहा। यह प्रदूषण बेहद खतरनाक है, जिसका असर लोगों के स्वास्थ्य और खेती पर बुरा असर पड़ रहा है। आइए जानते हैं कि आखिर समस्या क्या है? क्या होता है ओजोन प्रदूषण? तीन ऑक्सीजन अणुओं से बनने वाली ओजोन एक गैस है। ऊंचे आसमान में यहसूरज की हानिकारक किरणों से बचाती है, लेकिन जमीन के पास यह प्रदूषण बन जाता है। किसी स्रोत से यह सीधे नहीं निकलता है, बल्कि वाहनों, उद्योगों और बिजलीघरों से निकलने वाली नाइट्रोजन ऑक्साइड (NOx), वाष्पशील कार्बनिक यौगिक (VOCs) और कार्बन मोनोऑक्साइड (CO) के सूरज की रोशनी में रासायनिक प्रतिक्रिया से बनता है। यह बहुत प्रतिक्रियाशील गैस होती है, जो हवा में लंबी दूरी तक फैल सकती है। इससे यह शहरों से लेकर गांवों तक को प्रभावित करती है। कई शहरों में ओजोन का स्तर खतरनाक स्तर पर पहुंच गया रिपोर्ट के मुताबिक, इस साल मार्च-मई में कई शहरों में ओजोन का स्तर बेहद खतरनाक हो गया था। दिल्ली की रिपोर्ट पहले ही जारी की जा चुकी है। इसकी वजह से इस अध्ययन में उसे शामिल नहीं किया गया। बेंगलुरु में गर्मी के दौरान 92 दिनों में से 45 दिन ओजोन का स्तर मानक से अधिक रहा। यह बीते साल की तुलना में 29 फीसदी बढ़ा है। होमबेगोड़ा नगर सबसे ज्यादा प्रभावित क्षेत्र रहा। मुंबई की बात करें, तो 32 दिन ओजोन स्तर बढ़ा, जो साल 2024 की तुलना में 42 फीसदी कम है। चकाला सबसे प्रभावित इलाका रहा। कोलकातामें 22 दिन ओजोन स्तर बढ़ा। यहां भी बीते साल की तुलना में 45 प्रतिशत कम है। रवींद्र सरोवर और जादवपुर हॉटस्पॉट थे। हैदराबाद में 20 दिन ओजोन स्तर बढ़ा। यह बीते साल की तुलना में 55 फीसदी कम है। बोल्लारम सबसे ज्यादा प्रभावित रहा, जबकि चेन्नई में 15 दिन ओजोन स्तर बढ़ा, जो बीते साल शून्य था। यहां आलंदुर सबसे प्रभावित क्षेत्र र। इन शहरों में ओजोन का स्तर सर्दियों और अन्य मौसमों में भी बढ़ रहा है, खासकर गर्म जलवायु वाले इलाकों में। हर शहर में कुछ खास इलाकों में ओजोन का स्तर सबसे अधिक बढ़ता है। यहां पर प्रदूषण का असर और गंभीर होता है। ओजोन से सांस की नली को नुकसान पहुंचता है। अस्थमा और दमा जैसी बीमारियों को बढ़ाता है। इससे फसलों को भी नुकसान पहुंचता है।

• Urban Lab

Mega cities in India see high concentration of ozone pollution this summer

All mega cities in India, including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai, saw high concentration of ground-level ozone pollution this summer season, according to a new analysis by think tank Centre for Science and Environment (CSE). A previous analysis had shown that ozone, instead of particulate matter, was the main pollutant in Delhi's daily Air Quality Index (AQI) on several days this summer. The new analysis by the CSE's Urban Lab highlighted that ozone, unlike primary pollutants, is not released directly from any source. It forms through complex chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO), pollutants emitted by vehicles, power plants, industries and other sources of combustion. These substances react in the presence of sunlight, leading to the formation of ozone at the ground level. Anumita Roychowdhury, executive director at the CSE, said: "If unchecked, this can become a serious public health crisis as ozone is a highly-reactive gas and can be harmful even with short-duration exposures." She added that while cities in north India experience high ozone levels in summer due to intense heat and strong sunlight, cities in warmer climates are also seeing consistent ozone exceedance in other seasons. The current policy focus must be expanded to include improved monitoring, the mitigation of this toxic gas and a reduction in high local exposures. Ozone mitigation needs drastic control over a range of gases from vehicles, industry and all combustion sources, Roychowdhury said. Sharanjeet Kaur, deputy programme manager at the CSE's Urban Lab, said: "Inadequate monitoring, limited data and inadequate methods of trend analysis have weakened the understanding of this growing public health hazard across cities of India. Instead of merely averaging out the levels for the city, which is the standard practice to estimate the AQI, it is also important to adequately capture the high levels of local build-up and exposures in the hotspots and design mitigation strategies accordingly." Between March 1 and May 31 this year, Mumbai recorded ozone exceedance on 32 out of 92 days across its monitoring stations, a 42-per cent drop compared to the same period last year. The worst day in terms of spread was March 29, when eight out of 31 stations reported exceedance. The highest ground-level ozone concentration recorded was 90 micrograms per cubic metre. In Kolkata, ozone levels crossed the safe limit on 22 out of 92 days, a 45-per cent decline compared to last summer. The city also saw an overall improvement, with the average hourly ozone peak dropping by 22 per cent. Bengaluru saw ozone exceedance on 45 of the 92 days, a 29-per cent increase from last year. The worst day was March 31, when four of 14 stations recorded levels above the standard. Hyderabad recorded 20 ozone exceedance days, a 55-per cent drop compared to last summer. The highest ozone level recorded in the city was 51 micrograms per cubic metre. Chennai saw ozone exceedance on 15 days this summer. No such exceedance was reported during the same period last year. In comparison, the city had three exceedance days in 2023 and 19 in 2022. The highest level this year was 64 micrograms per cubic metre.

• Industrial Pollution

India Reverses Key Policy, Exempting Most Coal-fired Power Plants from Emission Rules

On 11 July, the Indian government changed its own rules, exempting most coal-fired power plants from installing technology to reduce sulphur dioxide (SO2) emissions. This reverses a key environmental policy launched in 2015 to cut SO2 emissions. It means that about 78% of India’s 537 or so thermal power plant units do not have to install machinery to reduce SO2 emissions called Flue Gas Desulfurization systems (FDGs). India is the largest SO2 emitter, mostly from such plants. The gas is an air pollutant linked to respiratory disorders and other health impacts, as well as ecological impacts such as acid rain. While the move has been questioned by experts, the government has hit back by denying that it is reversing the policy. In an X post, India’s environment ministry described criticism of the change as a “gross misinterpretation”, adding: “The revised sulphur dioxide emission policy is not a rollback” and that it remains “fully committed” to science-based air quality management: The report regarding the recent notification issued by the Ministry regarding the applicability of Sulphur Dioxide norms in respect of Thermal power Plants has been grossly misinterpreted. The norms of Sulphur Dioxide emissions from Thermal Power Plants notified on 11th July… pic.twitter.com/0aKpNaEXgy — MoEF&CC (@moefcc) July 14, 2025 Referring to an unnamed media report, the ministry added that it is “not aligned with empirical evidence, exaggerates the health and air quality impacts of sulphur dioxide, and underestimates the trade-offs of large-scale FGD implementation.” However, the near-total reversal of the policy “weakens pollution control efforts and endangers public health,” according to the Centre for Science and Environment, an environmental think tank. The new policy divides the thermal power plants into three categories. Of the 537 units which were supposed to get FGDs, now only 65 units (12%) must have these in category A. In the case of a further 66 units, category B, officials will determine on a case-by-case basis whether they need to install FGDs . The remaining 406 units, category C, are now exempted. This categorisation can be problematic. Similar pollution sources now have “different” environmental standards within India, points out an editorial in The Hindu newspaper. When the emission cuts were ordered in 2015, there was no such differentiation. All coal-fired power plants had to implement it. Herein, researchers point out, lies another significant dilution. Of the 36 coal-fired power units around Delhi, many have been shut down in the past during peak pollution times. However, 22 of them are now exempt from installing FGDs.

• Urban Lab

Ozone pollution surges across major Indian cities this summer, posing serious health risk

All mega cities in India, including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai, saw high concentration of ground-level ozone pollution this summer season, according to a new analysis by think tank Centre for Science and Environment (CSE). A previous analysis had shown that ozone, instead of particulate matter, was the main pollutant in Delhi's daily Air Quality Index (AQI) on several days this summer.All mega cities in India, including Kolkata, Bengaluru, Mumbai, Hyderabad and Chennai, saw high concentration of ground-level ozone pollution this summer season, according to a new analysis by think tank Centre for Science and Environment (CSE). A previous analysis had shown that ozone, instead of particulate matter, was the main pollutant in Delhi's daily Air Quality Index (AQI) on several days this summer. The new analysis by the CSE's Urban Lab highlighted that ozone, unlike primary pollutants, is not released directly from any source. It forms through complex chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO), pollutants emitted by vehicles, power plants, industries and other sources of combustion. These substances react in the presence of sunlight, leading to the formation of ozone at the ground level. Anumita Roychowdhury, executive director at the CSE, said: "If unchecked, this can become a serious public health crisis as ozone is a highly-reactive gas and can be harmful even with short-duration exposures." She added that while cities in north India experience high ozone levels in summer due to intense heat and strong sunlight, cities in warmer climates are also seeing consistent ozone exceedance in other seasons. The current policy focus must be expanded to include improved monitoring, the mitigation of this toxic gas and a reduction in high local exposures. Ozone mitigation needs drastic control over a range of gases from vehicles, industry and all combustion sources, Roychowdhury said. Sharanjeet Kaur, deputy programme manager at the CSE's Urban Lab, said: "Inadequate monitoring, limited data and inadequate methods of trend analysis have weakened the understanding of this growing public health hazard across cities of India. Instead of merely averaging out the levels for the city, which is the standard practice to estimate the AQI, it is also important to adequately capture the high levels of local build-up and exposures in the hotspots and design mitigation strategies accordingly." Between March 1 and May 31 this year, Mumbai recorded ozone exceedance on 32 out of 92 days across its monitoring stations, a 42-per cent drop compared to the same period last year. The worst day in terms of spread was March 29, when eight out of 31 stations reported exceedance. The highest ground-level ozone concentration recorded was 90 micrograms per cubic metre. In Kolkata, ozone levels crossed the safe limit on 22 out of 92 days, a 45-per cent decline compared to last summer. The city also saw an overall improvement, with the average hourly ozone peak dropping by 22 per cent. Bengaluru saw ozone exceedance on 45 of the 92 days, a 29-per cent increase from last year. The worst day was March 31, when four of 14 stations recorded levels above the standard. Hyderabad recorded 20 ozone exceedance days, a 55-per cent drop compared to last summer. The highest ozone level recorded in the city was 51 micrograms per cubic metre. Chennai saw ozone exceedance on 15 days this summer. No such exceedance was reported during the same period last year. In comparison, the city had three exceedance days in 2023 and 19 in 2022. The highest level this year was 64 micrograms per cubic metre. PTI GVS RC