Capping Delhi’s AQI: A Dangerous Illusion of Control

Capping Delhi’s AQI: A Dangerous Illusion of Control

Delhi’s officially reported Air Quality Index (AQI) has become less a measure of public health risk and more a tool of convenient understatement. By design, the AQI ceases to meaningfully differentiate pollution levels once they cross the “severe” threshold. Air that is catastrophically toxic is reduced to a single number, offering little sense of the escalating harm residents are forced to inhale each day.

While agencies such as the Delhi Pollution Control Committee continue to release real-time data on pollutants like PM2.5 and PM10, the translation of this data into public warning remains deliberately restrained. The AQI, rather than reflecting the true intensity of exposure, merely signals that the air is “hazardous”, without communicating how much worse it is becoming. In effect, capping the AQI dulls public perception of risk.

This numerical ceiling has provided the government a convenient shield. Officials often argue that the “official AQI has not crossed a certain limit,” that World Health Organization standards are only advisory, or that definitive links between pollution and disease are still being debated. Such claims ignore a vast body of global medical evidence and, more importantly, shift focus away from accountability and urgent action.

The result is widespread public confusion. A well-informed minority continues to raise alarms, citing medical research and lived experience. Meanwhile, many citizens move about unprotected, even as doctors and health experts issue repeated warnings. Mixed messaging and the absence of a clear emergency declaration have diluted the seriousness of the crisis in the public mind.

Behind this statistical calm, hospitals reveal the reality. Emergency rooms are witnessing a surge in respiratory and cardiac cases, particularly among children, the elderly, and those with pre-existing conditions. Yet, despite these warning signs, the government has stopped short of declaring a public health emergency or unveiling comprehensive mitigation and protection strategies.

Delhi’s air pollution crisis is no longer episodic, it is systemic. By capping the AQI, authorities risk normalizing an abnormal condition and postponing difficult policy decisions. Numbers that fail to reflect reality do not protect citizens; they endanger them. Transparency, truthful risk communication, and decisive intervention are no longer optional, they are overdue.

B S Vohra, Environment Activist President, East Delhi RWAs Joint Front, Delhi, India

The Crux of Delhi’s Air Pollution Crisis: B S Vohra, Environment Activist

The Crux of Delhi’s Air Pollution Crisis

Delhi’s air pollution crisis demands attention through two equally important and inseparable aspects: mitigation of pollution and saving precious lives. Treating one as more important than the other weakens the response. In a city where toxic air regularly exceeds safe limits, policy and action must move on both tracks at the same time.

Mitigation addresses the root causes of air pollution. It is the long-term solution that ensures future generations can breathe safely. In Delhi, major contributors include vehicular emissions, industrial pollution, construction dust, coal-based power, and seasonal stubble burning in neighboring states. Reducing pollution at the source requires structural change: cleaner fuels, electric public transport, strict emission norms, dust control at construction sites, and sustainable farming practices. Urban planning must reduce congestion and increase green spaces, while industries must be held accountable through continuous monitoring and penalties. Mitigation is slow, complex, and politically challenging, but without it, Delhi will remain trapped in a cycle of recurring pollution emergencies.

However, mitigation alone does not save lives in the present. Pollution levels in Delhi often reach hazardous levels where health damage occurs immediately. This brings us to the second equally vital aspect: protecting people and saving lives right now. Air pollution is not just an environmental issue; it is a public health emergency. Children, the elderly, outdoor workers, and those with heart or lung disease suffer the most. When air quality turns severe, hospitals fill with patients facing asthma attacks, heart stress, and respiratory infections. Many deaths linked to pollution are preventable with timely protection and healthcare access.

Saving lives requires emergency-style responses. High-pollution days should trigger health alerts, school closures, work-from-home advisories, temporary lock downs, and traffic restrictions. Hospitals must be prepared with adequate staff and resources, and treatment for pollution-related illness should be affordable or free during critical periods. Protective measures such as N95 masks, clean indoor air in schools and public buildings, and clear public guidance can significantly reduce harm. Clean-air shelters and indoor air filtration can provide relief in the worst-hit neighborhoods.

The central truth is this: people cannot be asked to sacrifice their health today in the hope of cleaner air tomorrow. At the same time, temporary protection without long-term mitigation only postpones the crisis. Delhi’s approach must recognize that every year of delay costs lives, productivity, and dignity.

Therefore, mitigation and life-saving measures must carry equal weight in planning, funding, and enforcement. Success should be measured not only by reduced pollution levels in the future, but also by fewer hospitalizations and deaths today. Clean air is a right, but until it is achieved, protecting human life must remain just as urgent.

Delhi does not have the luxury of choosing between cleaner air and saving lives. It must do both, together, immediately, and consistently. You cannot ask people to wait to breathe while mitigation slowly works. And you cannot save lives permanently without cutting pollution at its source.

Written by:

B S Vohra, Environment Activist, President, East Delhi RWAs Joint Front

We want constructive & not cosmetic measures to save Delhi from the grip of severe air pollution.

Delhi is facing an extremely grim situation due to hazardous + air pollution across the city. Officially reported AQI levels have crossed 465, i.e. over 30 times higher than WHO standards. Unofficially, and visibly, the AQI appears to be 60-80 times above safe limits. Despite this alarming crisis, authorities continue to play cosmetic GRAP measures across Delhi NCR.

The lives of crores of citizens are at serious risk due to life threatening medical emergency, yet there is no decisive action such as implementing vehicular odd-even measures to curb emissions. Schools continue in hybrid mode, masks are still not mandatory, and there is no consideration of a short lockdown to protect public health.

At the very least, the government could announce free Metro and DTC services and strongly discourage the use of private vehicles. Shockingly, no visible or constructive steps are being taken to safeguard the health of Delhiites.

"We want constructive & not cosmetic measures to save Delhi from the grip of severe air pollution", says B S Vohra, an Environment Activist, and President of the East Delhi RWAs Joint Front

While doctors advise residents to leave the city and courts shift to virtual hearings to avoid severe air pollution, offices and markets remain open in the name of protecting the economy. Water sprinklers are reportedly used near monitoring stations to downplay pollution severity, yet no advisories urge citizens to stay indoors. Meanwhile, air purifiers, now a basic necessity rather than a luxury, continue to attract an 18% GST.

Those in positions of power appear to lack a clear understanding of AQI, while the authorities tasked with its administration seem preoccupied with routine formalities rather than effective implementation.

The situation is dire, and superficial measures are insufficient to prevent serious respiratory and other health emergencies. There is a clear absence of political will and administrative resolve, making any meaningful improvement unlikely. Instead, authorities appear to be relying on seasonal changes and shifting wind patterns to provide temporary relief.

Using groundwater with uranium above 30 ppb (parts per billion) for cooking can pose health risks — mainly from chronic ingestion, not from external contact.

Here’s a clear, safe explanation:

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🚰 What happens if water with >30 ppb uranium is used for cooking?

✅ 1. Uranium does not evaporate or break down during cooking

When you boil rice, dal, vegetables, etc.:

• Water evaporates

• Uranium stays behind and becomes more concentrated in the food

So if the starting water has 30+ ppb, the final concentration in food may be even higher.

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⚠️ 2. Main health risk: Kidney damage (chemical toxicity)

The biggest concern is chemical toxicity, not radiation.

Long-term intake of uranium-contaminated water can cause:

• Damage to kidney tubules

• Increased creatinine levels

• Reduced filtration ability

• Protein/leakage in urine

This happens because uranium acts like a heavy metal toxin.

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⚠️ 3. Radiation risk is much smaller but not zero

Uranium gives off low-level alpha radiation. When ingested in small quantities, chemical toxicity happens much earlier than radiation harm.

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🍚 Does cooking make the contamination worse?

Yes. In foods like:

• Rice

• Tea

• Soups

• Lentils

The water volume reduces, but the uranium stays → higher concentration in the final food.

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👶 Who is most vulnerable?

• Children

• Pregnant women

• People with kidney disease

• Elderly

For them, even moderate exposure is more harmful.

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🛡️ Safe vs Unsafe Levels

• WHO guideline: ≤30 ppb in drinking water

• Many studies show kidney effects beginning near 15–30 ppb with chronic use

Cooking water should ideally meet the same standards as drinking water.

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🏠 What can you do? (Practical solutions)

✔️ Safe options

• Use RO water (RO removes 90–99% uranium)

• Use bottled water for drinking + cooking

• Use community RO plants

• Test your groundwater every 6–12 months

❌ Boiling water does NOT remove uranium

It actually increases concentration.

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🧪 Should you stop using your current groundwater for cooking?

If uranium >30 ppb:
👉 Yes — avoid using it for drinking and cooking.

Use RO-treated or alternative water.

B S Vohra

Environment Activist

500 से 999 और उस के भी ऊपर वाला AQI किस केटेगरी में आता है ?

 CPCB के मानकों के अनुसार, शून्य से 50 के बीच AQI ‘अच्छा’, 51 से 100 ‘संतोषजनक’, 101 से 200 ‘मध्यम’, 201 से 300 ‘खराब’, 301 से 400 ‘बहुत खराब’ और 401 से 500 के बीच एक्यूआई ‘गंभीर’ माना जाता है। 

लेकिन 500 से 999 और उस के भी ऊपर वाला AQI किस केटेगरी में आता है ?

B S Vohra

East Delhi RWAs Joint Front;

Delhi RWAs Pollution Control Committee (DRPCC)

Delhi RWAs Pollution Control Committee (DRPCC) Formed to Tackle Capital’s Worsening Air Crisis

PRESS RELEASE

Delhi RWAs Pollution Control Committee (DRPCC) Formed to Tackle Capital’s Worsening Air Crisis

In a decisive move to confront Delhi’s escalating air pollution emergency, B. S. Vohra, an Environment Activist, & President of the East Delhi RWAs Joint Front, as well Convener of the RWA Bhagidari Network, has announced the formation of the Delhi RWAs Pollution Control Committee (DRPCC).

Vohra stated that the new committee has been established to address the crisis far more seriously and systematically than it has been so far.

“Despite the ongoing efforts of CAQM, CPCB, and DPCC, why does Delhi’s air quality continue to deteriorate year after year?” he asked. “Does this mean their actions are ineffective, or merely symbolic, lacking real impact?”

Highlighting the stark difference between past achievements and today’s grim reality, Vohra noted:

“In 2010, Delhi successfully hosted the Commonwealth Games. But in 2025, even the BCCI has opted to skip the Under-23 tournament due to pollution concerns.”

He added that the crisis has now reached a point where doctors are advising residents to relocate, and courts have shifted to virtual hearings to safeguard public health.

“Every year, thousands suffer from life-threatening medical conditions linked to pollution, yet authorities still fail to enforce strong, protective measures,” Vohra said.

Concluding with a powerful message, he posed a critical question that reflects the city’s growing frustration:

“Is there no one in the system who can be held accountable for this disaster?”

Vohra added that like-minded RWAs, domain experts, and citizen groups will be brought into the committee, strengthening a collective and sustained movement to save Delhi from the growing threat of air pollution.

By:

DELHI RWAs POLLUTION CONTROL COMMITTEE (DRPCC) 🙏👍💯😭

How the Air Pollution levels keep worsening in the national capital city DELHI ?

The worsening air pollution in Delhi, despite the efforts of organizations like the Commission for Air Quality Management (CAQM), Central Pollution Control Board (CPCB), and Delhi Pollution Control Committee (DPCC), is a complex issue with multiple contributing factors. Here's a breakdown of some of the key reasons:

1. Vehicular Emissions

Number of Vehicles: The sheer volume of vehicles on the roads is a major contributor. Delhi has one of the highest numbers of vehicles in the country. Even with stricter emission norms and initiatives like the odd-even scheme, the number of vehicles continues to rise.

Diesel Trucks: Delhi serves as a major transportation hub, and a significant amount of pollution is caused by heavy diesel trucks passing through the city. Diesel engines emit large amounts of particulate matter (PM), nitrogen oxides (NOx), and other harmful gases.

2. Construction and Development

Construction Dust: With rapid urbanization, construction work is constantly happening in Delhi. Dust from construction sites is a significant contributor to air pollution, especially particulate matter (PM10 and PM2.5), which is harmful to health.

Infrastructure Projects: Large-scale infrastructure projects, like the Delhi Metro expansion, flyovers, and housing complexes, often lead to an increase in dust and emissions during their construction phases.

3. Burning of Crop Residue (Stubble Burning)

Neighboring States: A significant portion of Delhi's air pollution during the winter months (October-November) is driven by the burning of crop residues in neighboring states like Punjab, Haryana, and Uttar Pradesh. While efforts have been made to incentivize farmers to stop burning stubble, this practice continues due to economic and logistical constraints.

4. Industrial Emissions

Unregulated Industries: Despite efforts to regulate industrial pollution, many small and medium-sized industries around Delhi continue to operate with outdated, inefficient equipment, emitting large quantities of pollutants.

Power Plants and Boilers: Many coal-powered plants and boilers continue to contribute significantly to the pollution levels in and around the city.

5. Weather and Geography

Temperature Inversion: In winter, Delhi experiences temperature inversion, where a layer of warmer air traps cooler air near the surface. This phenomenon prevents pollutants from dispersing, causing them to accumulate and intensify air pollution.

Wind Patterns: The wind direction and speed during certain months can concentrate pollution in the city. Additionally, the local topography can trap pollutants, exacerbating the situation.

6. Firecrackers and Festivities

Diwali and Other Festivals: Every year, during festivals like Diwali, the bursting of firecrackers results in a sharp increase in air pollution, particularly in the form of particulate matter (PM2.5 and PM10). Despite public awareness campaigns, the practice continues to be widespread.

7. Waste Management Issues

Open Burning of Waste: The burning of waste, including plastic and other materials in landfills or on roadsides, is a common practice in Delhi. This adds to the toxic mix of pollutants in the air.

Garbage Piles: Inefficient waste management leads to the accumulation of garbage, which, when burnt, contributes to the city's poor air quality.

8. Insufficient Enforcement of Regulations

Weak Implementation: While there are many laws and regulations in place (e.g., restricting the use of stubble burning, encouraging cleaner fuels, or limiting construction dust), enforcement remains a challenge. There are instances of non-compliance by industries, construction sites, and even individuals, which contribute to the pollution.

Political and Bureaucratic Challenges: Air pollution is a politically sensitive issue, and different state and central authorities often have conflicting interests or insufficient coordination.

9. Climate Change and Long-term Changes

Increased Frequency of Extreme Events: Climate change is leading to more erratic weather patterns, making certain pollutants more concentrated during specific times of the year (e.g., longer periods of fog and stagnation in winter).

Long-Term Pollution Trends: Many of Delhi's pollution challenges are tied to years of industrialization, urbanization, and unchecked emissions. The long-term effects are difficult to reverse quickly.

10. Public Awareness and Behavioral Challenges

Public Behavior: Many individuals still don't fully understand the severity of the issue or how their actions (e.g., burning leaves, excessive use of private vehicles, improper waste disposal) contribute to pollution.

Lack of Alternative Options: Public transportation infrastructure, although improving, is still inadequate in many areas. People rely on private cars, contributing to traffic emissions. Moreover, affordable electric vehicle (EV) infrastructure is still in the developmental stage.

Efforts Being Made

Despite these challenges, several steps are being taken:

Graded Response Action Plan (GRAP): A framework to tackle air pollution with increasing severity depending on the pollution levels.

Air Quality Index (AQI) Monitoring: Real-time monitoring and reporting systems to provide timely information to the public.

Promotion of Electric Vehicles: Incentives to promote EVs and transition to cleaner energy sources.

Public Awareness Campaigns: Continuous campaigns to educate the public about the importance of reducing pollution.

Conclusion

The situation in Delhi is the result of a combination of socio-economic, environmental, and regulatory factors. While there have been improvements in certain areas (such as stricter vehicle emission standards and cleaner energy initiatives), the city is still grappling with pollution because of the complex and interconnected nature of the problem. The road to cleaner air will require stronger enforcement, systemic changes, better coordination among agencies, and more sustainable urban planning, all while balancing economic growth and the welfare of the population.

B S Vohra, Environment Activist, President, East Delhi RWAs Joint Front

दिल्ली का घुटता दम: गंभीर वायु प्रदूषण से बढ़ता खतरा !

दिल्ली में हर वर्ष सर्दियों के मौसम में वायु प्रदूषण एक गंभीर संकट के रूप में सामने आता है। हवा में घुले विषैले प्रदूषक न केवल पर्यावरण को नुकसान पहुँचाते हैं, बल्कि मानव स्वास्थ्य, अर्थव्यवस्था और सामान्य जीवन पर भी गहरा प्रभाव डालते हैं। दिल्ली का एयर क्वालिटी इंडेक्स (AQI) अकसर ‘सीवियर’ श्रेणी में पहुँच जाता है, जो यह दर्शाता है कि हवा में मौजूद कण (PM2.5 और PM10) सुरक्षित स्तर से कई गुना अधिक हैं। यह स्थिति दिल्ली-एनसीआर के करोड़ों लोगों के लिए अत्यंत हानिकारक है।

सबसे पहले स्वास्थ्य पर पड़ने वाले दुष्प्रभावों की बात करें तो वायु प्रदूषण फेफड़ों और हृदय से जुड़ी बीमारियों को बढ़ावा देता है। लगातार प्रदूषित हवा में सांस लेने से खाँसी, सांस फूलना, आंखों में जलन, एलर्जी और अस्थमा जैसी समस्याएँ तेजी से बढ़ती हैं। बच्चों, बुजुर्गों और गर्भवती महिलाओं के लिए यह स्थिति और भी खतरनाक होती है। 

लंबे समय तक ऐसे वातावरण में रहने से फेफड़ों की कार्यक्षमता घट जाती है और हृदय संबंधी रोगों का जोखिम बढ़ जाता है। कई मामलों में गंभीर प्रदूषण का प्रभाव क्रोनिक ऑब्सट्रक्टिव पल्मोनरी डिजीज (COPD) और फेफड़ों के कैंसर तक भी पहुँच सकता है। डॉक्टरों के अनुसार, दिल्ली में शीतकाल के दौरान श्वसन संबंधी मरीजों की संख्या कई गुना बढ़ जाती है, जिससे अस्पतालों पर भी अतिरिक्त दबाव पड़ता है।

दूसरा बड़ा नुकसान पर्यावरण पर पड़ता है। वायु प्रदूषण से पेड़ों की पत्तियाँ समय से पहले झड़ने लगती हैं और पौधों की वृद्धि प्रभावित होती है। हवा में मौजूद सल्फर डाइऑक्साइड और नाइट्रोजन ऑक्साइड जैसे प्रदूषक अम्लीय वर्षा का कारण बनते हैं, जो मिट्टी और जलस्रोतों को भी हानि पहुँचाती है। प्रदूषण की अधिकता से दिल्ली के चारों ओर मौजूद हरियाली पर भी बुरा असर पड़ता है। इसके अलावा, हवा में धुंध और स्मॉग की परत सूर्य की किरणों को रोक देती है, जिससे तापमान में असामान्य बदलाव देखने को मिलता है और मौसम चक्र प्रभावित होता है। यह स्थिति जलवायु परिवर्तन की समस्याओं को और बढ़ा देती है।

वायु प्रदूषण का आर्थिक प्रभाव भी कम नहीं है। बढ़ती बीमारियों के कारण लोगों को इलाज पर अधिक खर्च करना पड़ता है और कई बार कामकाजी दिनों का नुकसान भी होता है। स्कूलों और कार्यालयों को बंद करने की स्थिति पैदा हो जाती है, जिससे शिक्षा और व्यापार दोनों प्रभावित होते हैं। निर्माण कार्यों और वाहन उपयोग पर लगाए गए प्रतिबंधों से व्यवसायिक गतिविधियाँ धीमी पड़ जाती हैं। प्रदूषण के कारण पर्यटकों की संख्या भी घटती है, जो दिल्ली की अर्थव्यवस्था के लिए चिंताजनक है।

अंततः, सामाजिक जीवन भी इस प्रदूषण का शिकार होता है। लोग बाहरी गतिविधियों से बचने लगते हैं, बच्चे मैदानों में खेल नहीं पाते और सामान्य जीवनशैली प्रभावित होती है। मास्क पहनना अनिवार्य हो जाता है और स्वच्छ हवा जैसी बुनियादी आवश्यकता भी एक चुनौती बन जाती है।

संक्षेप में, दिल्ली में गंभीर वायु प्रदूषण स्वास्थ्य, पर्यावरण, अर्थव्यवस्था और समाज—चारों स्तरों पर भारी नुकसान पहुँचाता है। इस समस्या से निपटने के लिए सरकार, उद्योगों और नागरिकों सभी को मिलकर दीर्घकालिक समाधान अपनाने होंगे, जैसे—स्वच्छ ऊर्जा का उपयोग, सार्वजनिक परिवहन को बढ़ावा, वृक्षारोपण और प्रदूषण नियंत्रण नियमों का कड़ाई से पालन। केवल सामूहिक प्रयासों से ही दिल्ली को स्वच्छ और स्वस्थ हवा मिल सकती है।

B S Vohra, Environment Activist President, East Delhi RWAs Joint Front

What aqi level in Delhi can cause permanent damage of Lungs?

What aqi level in Delhi can cause permanent damage of Lungs?

Here's a clear, safe, and science-based explanation:

AQI Levels and Risk of Permanent Lung Damage

The Air Quality Index (AQI) uses the same health-impact categories worldwide (including Delhi), though Delhi often reaches the highest bands. Permanent lung damage is not tied to a precise AQI number, but the risk increases sharply at very high and prolonged exposures.

Below is the standard interpretation:

AQI Level	Category	Health Effects	Risk of Long-Term / Permanent Damage
0–100	Good/Moderate	Minimal	None expected
101–200	Unhealthy for Sensitive Groups	Irritation, reduced lung function (temporary)	Long-term exposure can begin affecting children, elderly, and asthmatics
201–300	Unhealthy	Breathing difficulty for most people	Chronic exposure may cause measurable decline in lung function
301–400	Very Unhealthy	Significant respiratory distress	High risk of long-term lung damage, especially with repeated or continuous exposure
401–500+	Hazardous / Severe	Serious health effects on everyone	Prolonged exposure can lead to permanent lung damage, increased risk of COPD, and long-term impairment

So, what AQI level in Delhi can cause permanent lung damage?

➡️ Short-term spikes (even 500+) usually do not cause permanent damage alone, but
➡️ Repeated or long-term exposure to AQI above ~300–400 greatly increases the risk of lasting or permanent lung damage, especially from PM2.5.

Why?

PM2.5 particles (most responsible for Delhi pollution peaks) can:

• lodge deep inside the alveoli,

• cause chronic inflammation,

• reduce lung growth in children,

• accelerate lung aging,

• increase lifetime risk of asthma, COPD, and heart disease.

Important note

This information is for general education, not medical diagnosis. If you have symptoms (persistent cough, breathlessness, wheezing), consulting a medical professional is recommended.

B S Vohra, Environment Activist, President, East Delhi RWAs Joint Front

Causes of Day Time severe Air Pollution in Delhi ?

Delhi’s hazardous daytime air pollution results from a combination of human activities and natural factors. The major causes include:

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1. Vehicular Emissions

• High population and rapid growth in vehicle ownership.

• Traffic congestion leads to idling, increasing emissions.

• Major pollutants: PM2.5, PM10, NOx, CO, and ozone precursors.

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2. Industrial and Power Plant Emissions

• Factories around Delhi-NCR emit particulate matter, sulfur dioxide (SO₂), and nitrogen oxides (NOx).

• Brick kilns and small-scale industries often use dirty fuels like coal, wood, and furnace oil.

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3. Construction and Road Dust

• Continuous construction, demolition, and poor dust-control practices release large amounts of PM10.

• Road dust resuspension due to traffic movement is one of the largest daytime contributors.

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4. Biomass Burning Within the City

• Burning of garbage, wood, and crop waste inside Delhi’s informal settlements contributes to toxic emissions.

• Open waste burning is a major source of black carbon.

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5. Stubble Burning (Seasonal but Severe)

• Farmers in Punjab, Haryana, and Uttar Pradesh burn rice stubble.

• Winds carry the smoke to Delhi, dramatically raising PM2.5 levels, especially in late October–November.

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6. Atmospheric and Weather Conditions

• Low wind speed during the day traps pollutants.

• Temperature inversions can occur even in daytime winter months, preventing vertical dispersion.

• Strong sunshine triggers photochemical reactions, increasing ground-level ozone.

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7. Urban Heat Island Effect

• Dense built-up areas trap heat, intensifying chemical reactions that form secondary pollutants like ozone and secondary PM2.5.

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8. Diesel Generators

• Commonly used during power cuts in markets, construction sites, and residential complexes.

• Emit high levels of PM2.5, SO₂, and NOx.

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9. Poor Fuel Quality & Waste Disposal Practices

• Use of substandard fuels in transport and industry.

• Improper waste disposal leads to open burning, especially during daytime when enforcement is weak.

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Summary

Delhi’s hazardous daytime air pollution arises from a mix of local emissions (vehicles, dust, industries), regional sources (crop burning), and weather conditions that trap pollutants and enhance photochemical pollution.

B S Vohra, Environment Activist, President, East Delhi RWAs Joint Front

Why is night AQI worse in Delhi?

How night aqi is higher in Delhi comparing day AQI, even though minimum vehicular emissions and parali fires can't impact only during night ?

There are clear scientific reasons why AQI in Delhi is often higher at night than during the day, even when traffic emissions are low and stubble-burning (“parali”) isn’t occurring at that exact time.

Here’s the explanation, step by step:

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🌆 1. Night-time temperature inversion traps pollutants

This is the main reason.

• After sunset, the ground cools quickly.

• The air near the surface becomes colder than the air above it.

• Cold air is heavier and cannot rise - this creates a temperature inversion layer.

• Pollutants from day sources (vehicles, industry, dust, residual biomass smoke) get trapped near the ground, causing AQI to spike.

During the day:

• Sunlight heats the ground → warm air rises → vertical mixing occurs.

• Pollutants disperse upward → AQI appears better.

➡️ Even if emissions are low at night, the inability of pollutants to disperse makes the concentration appear higher.

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🌬️ 2. Wind speed is lowest at night

• Night-time winds tend to calm significantly in plains cities like Delhi.

• With low or no wind, pollutants accumulate locally.

• Even residual pollution from the daytime stays close to the surface.

Daytime winds + sunlight = better dispersion.

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🏭 3. Continuous emissions (even at lower levels) still accumulate

Even though traffic decreases, these sources continue throughout the night:

• Waste burning (often done at night)

• Industrial emissions (not all factories shut down)

• Construction dust

• Domestic emissions (heating, cooking, generators)

• Heavy trucks enter Delhi mostly at night (unless restricted)

Lower emissions + zero dispersion still leads to higher concentration.

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🌫️ 4. Higher humidity at night forms secondary particles

At night Delhi’s humidity rises. Higher humidity promotes:

• Formation of secondary particulate matter (especially PM2.5)

• Hygroscopic growth of existing particles → they absorb moisture and get “bigger”

• Fog + particulate interaction → smog

This increases PM2.5 readings even if pollution source is unchanged.

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🔥 5. Parali (stubble burning) affects nights more due to wind patterns

Even though fires may occur in the day, their transport to Delhi often peaks at night:

• Cooler night winds from Punjab/Haryana bring smoke into Delhi.

• Unable to disperse due to inversion, the smoke accumulates.

So fires don’t have to happen “at night” to worsen night AQI.

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🌃 6. Chemical reactions differ between day & night

Daytime sunlight causes photochemical reactions that help break some pollutants (like NOx).
At night:

• No sunlight → fewer reactions to degrade pollutants.

• NO₂ builds up because it isn't photolyzed.

• Ozone decreases at night, affecting secondary particle formation dynamics.

Overall effect → pollution stays in its most concentrated form.

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✔️ In summary: Why is night AQI worse in Delhi?

Even with lower emissions, pollutants get trapped, accumulate, grow, and don’t disperse at night due to:

• Temperature inversion

• Low wind speed

• Increased humidity

• Residual emissions accumulating

• Transport of pollution from outside Delhi

• Suppressed chemical breakdown of pollutants

This phenomenon is common in polluted cities worldwide, but Delhi’s geography and winter conditions amplify it dramatically.

B S Vohra, Environment Activist, President- East Delhi RWAs Joint Front