For many residents of Delhi-NCR, waking up the morning after Diwali this year felt surprisingly different. The air didn’t sting the eyes, visibility seemed clearer, and there wasn’t the same heavy, smoky blanket that has often shrouded the city after the festival of lights.
Social media buzzed with comments like “This Diwali morning feels much cleaner than before” and “The air seems better this time.” Yet when people checked the Air Quality Index (AQI) data later that day, the numbers told another story.
In several parts of Delhi, the AQI continued to remain in the ‘severe’ or ‘very poor’ category — crossing 400 to 450 in some zones. That led to an obvious question: if the air felt cleaner, why did the data say otherwise?
The answer lies in a mix of science, weather patterns, and human perception — and experts say it’s quite normal for what we feel to differ from what instruments record.
The Illusion of “Cleaner” Air — How Our Senses Can Mislead Us
The first thing to understand, scientists say, is that human perception of air quality is not always accurate.
When people step outside after Diwali night and don’t immediately smell smoke or see visible haze, they often assume the air is cleaner. But absence of smell or visible smog doesn’t mean the air is safe or pollutant-free.
According to Dr. Gufran Beig, founder of SAFAR (System of Air Quality and Weather Forecasting and Research),
“Our sensory organs can detect larger particles and strong odors, but the most dangerous pollutants — like PM2.5 — are invisible and odorless. You can’t see or smell them, but they enter deep into your lungs.”
These ultrafine particles (smaller than 2.5 micrometers) make up a large part of post-Diwali pollution. Even when the sky looks clearer, PM2.5 levels can still be several times higher than the safe limit.
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Meteorology Plays a Big Role
The weather conditions during and after Diwali play a decisive role in determining how the pollution behaves.
If the night is cool, calm, and still, the pollutants from firecrackers and vehicles get trapped close to the ground because of a phenomenon called temperature inversion. This is when a layer of warm air sits above cooler air near the ground, preventing pollutants from dispersing.
On the other hand, if there’s wind movement, even moderate, it can disperse the smoke faster, making the air appear cleaner — even though the overall pollution levels might remain high when measured over 24 hours.
Meteorologist Mahesh Palawat from Skymet explains,
“The morning breeze can make the air seem fresh, but the pollutants are still there. They’re just spread over a wider area. That’s why your nose may not sense it, but instruments still pick up high AQI readings.”
This year, wind speeds over Delhi were slightly better than the past few Diwalis — around 6 to 8 km/h — which helped disperse visible smoke faster. However, the fine particulate concentration remained high throughout the night and early morning, pushing the AQI into the ‘severe’ range despite the improved visibility.
The AQI Reflects a 24-Hour Average — Not Just the Morning Air
Another important reason for the “difference in feeling” comes from how AQI is calculated.
The Air Quality Index is based on the average concentration of key pollutants (like PM2.5, PM10, NO₂, SO₂, CO, and ozone) measured over a specific period — usually 24 hours.
So, even if the air seemed better on Diwali morning, the AQI value still included the extremely high pollution levels recorded during the night, when fireworks peaked.
In short, the “morning freshness” you feel doesn’t erase what happened the night before — the AQI number reflects the total exposure over the previous day.
As environmental scientist Rohini Pande explains,
“Think of it like a report card. The AQI is an average score for the whole day, not just the morning test. Even if things look better now, the overall grade remains poor.”
Firecracker Pollution Is Short-Term but Intense
Firecracker emissions are episodic — they spike sharply for a few hours but fade quickly once burning stops. However, during those hours, the concentration of PM2.5 and PM10 shoots up to 10–20 times higher than normal levels.
While the visible smoke clears fast with wind and daylight, the fine particles remain suspended in the atmosphere for hours or even days, contributing to sustained poor AQI readings.
This is why, even when people wake up to a seemingly “clearer” sky the next morning, the pollution monitors continue to flash red warnings.
Diwali 2025: Slightly Better Than Previous Years, But Still Critical
According to early reports from SAFAR and the Central Pollution Control Board (CPCB), the overall air quality in Delhi this Diwali was slightly better than last year’s, though still in the ‘severe’ category.
Average PM2.5 levels dropped marginally — from around 430 µg/m³ in 2024 to about 390 µg/m³ this year — thanks to stronger winds and light pre-Diwali rain that helped clean the air temporarily.
However, experts caution against complacency.
“Better than last year doesn’t mean good,” says Dr. Beig. “The safe limit for PM2.5 is just 60 µg/m³. We are still six times higher than that. Every year, we celebrate improvement from disaster to slightly less disaster — that’s not real progress.”
Crop Burning Adds to the Mix
Diwali coincides with the stubble-burning season in Punjab and Haryana, which contributes significantly to Delhi’s pollution load.
Satellite data showed over 2,500 farm fire incidents during Diwali week this year — slightly fewer than last year but still enough to add a substantial layer of smoke over northern India.
These pollutants mix with local emissions from fireworks, vehicles, and industrial activity, creating a toxic cocktail that lingers in the air long after the festival ends.
Psychological Factors: The Diwali Mood Effect
There’s also a psychological angle to this perception gap. During festivals, people are in high spirits, surrounded by lights, colors, and celebrations. Their senses are engaged, and they are less likely to focus on the discomfort caused by pollution.
After the festivities, the relief of calm weather and quieter surroundings can make the air feel cleaner. This is a well-known cognitive bias called contrast perception — when our brain compares the current situation to the intense conditions just hours earlier.
So, if the night was filled with smoke and noise, even slightly clearer air the next morning feels dramatically better — though scientifically, it may still be hazardous.
The Real Message: What We Feel Isn’t Always What We Breathe
The key takeaway is that human perception cannot replace scientific data. Even if the air looks and feels cleaner, the invisible pollutants still pose serious health risks — especially to children, the elderly, and those with respiratory problems.
Health experts recommend using N95 masks, air purifiers, and avoiding early-morning outdoor activities for several days after Diwali, when pollutant levels remain high despite improved visibility.
As environmentalist Sunita Narain from CSE puts it:
“The air doesn’t have to look gray to be deadly. The most dangerous particles are the ones you can’t see.”
Moving Forward: A Need for Consistent Action
While Delhi may have seen a marginal improvement this Diwali, experts stress that temporary relief isn’t real progress. Long-term solutions — such as cleaner public transport, strict control on construction dust, and better stubble management — remain the only way forward.
Banning firecrackers alone cannot solve the problem, but enforcing the ban effectively and combining it with strong emission control policies can make a difference over time.
Conclusion
The morning after Diwali may have felt cleaner to many Delhiites this year — but the data reminds us that perception can be deceptive. What felt like a breath of relief was, in reality, air still loaded with invisible, harmful particles.
Science tells us that only consistent, collective action can make a true difference — not just clearer mornings, but truly cleaner air for everyone.
