Heatwaves Trigger Hidden Ozone Threat

'Can you believe there are over 26,500 deaths linked to heatwave-driven ozone in 2024?'

Super El Nino is here. And India has already started seeing the impact on its climate.

In May 2026, in the global list of hot cities in the world, 97 out of 100 were in India.

Reports say that three quarters of India's labour force, engaged in agriculture and construction, are exposed to such extreme heat conditions.

Along with heat is pollution. According to AQI.in's Real-time Most Polluted Cities in the World 2026 rankings, 21 out of 25 world's most polluted cities are in India.

Now comes the ozone effect.

For the first time a study led by Professor Jayanarayanan Kuttippurath and Parambat Sangeetha from IIT Kharagpur titled Heatwaves Trigger Severe Surface Ozone Pollution In India: Regional Hotspots, Trends And Health Effects Heatwaves trigger severe surface ozone pollution in India: regional hotspots, trends and health effects (external link)

Jayanarayanan Kuttipurath is an associate professor at the Centre for Ocean, River, Atmosphere and Land Science (CORAL), IIT Kharagpur.

"Making people aware of all this is very important. Without awareness, you can't tide over the crisis," Professor Kuttipurath tells Rediff's Shobha Warrier.

Ground-Level Ozone Explained

Your study says heat waves in India can trigger surface ozone surges. It is generally said that ozone layer is in the stratosphere. How does ozone come to the ground level when there is extreme heat?

The stratosphere is about 15 km up to 50 km from the earth's surface. In this region ozone is produced directly.

But below 15 km, up to the surface, ozone is not produced directly. But there will be indirect reaction.

If we have more pollutants in the atmosphere, they can react with each other in presence of analyte and make ozone.

That is very bad because compared to stratosphere, the tropospheric ozone is very small in quantity but it has very harmful effect on health.

It is said that in the stratosphere, ozone layer protects the earth from harmful UV rays. How does the ozone layer become harmful when it is at the ground level?

That is because when ozone is at the ground level, we inhale it.

Ozone production is maximum in the stratospheric region. In other words, there is more ozone in the stratosphere and when more sunlight hits the region, ozone absorbs the UV radiation.

Ozone is reactive everywhere in the atmosphere, but in the stratosphere it forms a stable protective UV shield through a natural formation-destruction cycle whereas in the troposphere it is generated from pollution and sunlight, accumulating near the surface where it can harm human health.

All chemical reactions are wavelength and frequency dependent. Those rays with longer wavelength comes to the surface.

Since most of the ozone is already absorbed in the stratosphere, only a very small amount comes to the next region.

What happens when ozone is produced at the ground level?

The ground level ozone production happens when there are hazardous air pollutants like Nitrogen dioxide (NO₂) and Volatile Organic Compounds (VOCs) which react in sunlight to form ground-level ozone.

VOCs are a large group of carbon-based chemicals that are airborne gases released by vehicles, industrial products, etc.

The volatile organic compounds or VOCs react in presence of sunlight and make ozone.

The process happens at the surface level where we live.

The result is we inhale and results in diseases like asthma, chronic obstructive pulmonary diseases.

Why Heatwaves Increase Ozone

Does the ozone production happen all the time, or only when the heat is extreme?

Ozone production happens all the time in the polluted regions whether there is extreme heat or not.

For example in cities where there are more pollutants, more NO₂, more VOCs, you have more ozone as well. You don't need heat waves for ozone production.

Let me also say that all these chemical reactions are also temperature dependent. So if there is high temperature, reactions will be faster, and ozone is produced faster.

When you have heat waves, you have more sunlight and more heat. It also means reactions will be faster. So in that region, there will be more ozone.

India's Emerging Health Crisis

On May 26, day temperature broke the 176 year heat record. And in some of the areas in India, temperature touched 50 degrees. In such a situation, how much does it affect human beings other than dehydration and all the problems associated with extreme heat?

When you have 50 degrees, you will be dehydrated and can get heat strokes.

Such a situation is very dangerous for the elderly, children and those with other existing health problems like lungs related diseases, asthma, etc. Extreme heat is extremely dangerous.

What will happen when you have high heat and high pollution?

Ozone formation will be higher there, and this will also create more health problems.

High heat, high level of pollution and high level ozone can amplify all the health problems.

This is the most dangerous part.

Till now, people thought heat waves are just extreme heat, and if you drink lots of water and not go out, it is fine.

Thery were unaware of the ozone effect.

Our study went through the heatwave events from 2004-2024, and found that the surface ozone concentrations during heatwaves frequently reach 85-110 μg m⁻³, exceeding the World Health Organization guidelines.

This is across all the regions in India.

And the most severe hotspots include Northwest India, the Indo-Gangetic Plain, North-Central India, the Northeast, and the Western Himalaya. Ozone levels in these regions exceed WHO limits by 39 to 45 per cent, peaking at an alarming 115 per cent in the Western Himalayas.

In addition, these regions are also highly polluted with 40 to 45 per cent NO₂ from vehicles and industries, in addition to VOCs.

So, the situation is conducive for more production of ozone.

High pollution area means high presence of ozone as well.

So in addition to high heat, they also have ozone related health problems.

It means the effect on health will be amplified in these highly polluted regions.

Has the ozone effect been happening for quite some time or is it a recent phenomenon? Till now, nobody spoke about the ill-effects of ozone.. We only heard about the ill-effects of extreme heat and pollution.

That is the point of publishing this paper. That is why this paper is important, and this study is important.

This is the first study on ozone and heat wave effect.

Ours is a long term study. So, it's a long-term analysis.

How much has it affected the people in India?

Can you believe there are over 26,500 deaths linked to heatwave-driven ozone in 2024?

In 2024 alone, ozone exposure during heatwaves was associated with 15,615 deaths from Ischemic Heart Disease (IHD) and 10,898 deaths from Chronic Obstructive Pulmonary Disease (COPD)

This amounts to a combined mortality burden of over 26,500 deaths.

Compared to the pre-heatwave conditions, heatwaves contributed an additional 490 IHD deaths and 342 COPD deaths.

This is a matter of great concern and it is a health-threat for a country like India.

Ozone Forecasting Urgently Needed

In what way can the country face it?

See, we have a heat action plan, and all the states have implemented it. So, IMD has a heatwave forecast.

But they do not have an ozone forecast.

So, there has to be some urgent reforms like the Integration of ozone forecasting systems, Inclusion of air-quality health advisories and development of combined climate-air pollution response strategies.

If there is a warning about the areas where there will be high ozone, like they do for heat waves, people can avoid going to the area and not get exposed.

Those who are more vulnerable are the old people, children and those with existing health conditions.

So, we feel a forecast is very important.

Which is more hazardous, extreme heat or air pollution or ozone?

Just imagine that you are in a city and the temperature there is 35 degrees.

Added to that is an air pollution level of 100 to 120 micrograms per cubic meter (μ g/m³) which can be termed as unhealthy air quality.

When you have ozone also, it becomes more dangerous.

Then you have 47 degree temperature in a desert region but you do not have that much ozone pollution there. Heat is the main villain there.

So the danger depends on where you are.

In cities where there are more vehicles and industries, there will be more pollutants in the air. By default, there you will have ozone pollution as well.

We know ozone is dangerous, and heat is also dangerous. So avoid both heat and ozone. That is the best way.

Climate Change Raises Risks

What precautions should people take?

First of all, we have to reduce pollution. We have to cut down the emissions. Emissions in the sense, greenhouse gas emissions.

You mean whatever people are supposed to do to face climate change, they should do to prevent ozone effect also?

See, temperature is rising due to global warming and it will be higher in coming years, for sure.

We are also polluting each day because more rural regions are annexed to city regions, and cities are expanding.

When you have more people, more anthropogenic activities, more factories, and more vehicles, it means more pollution and more ozone.

The only way you can control this is, we have to cut emission and reduce air pollution. We have to find ways to do that

IMAGE: Professor Jayanarayanan Kuttippurath. Photograph: Kind courtesy Professor Jayanarayanan Kuttippurath

Is India more at risk compared to other countries because of the number of people and also the number of vehicles?

Definitely. Also, more people are exposed to pollution of all kinds.

For example, Delhi have 50 lakh or 1 crore people residing while in some other country, in a city, you have 1 lakh people or 5 lakh people.

It means more people will be exposed even if the ozone is same amount,  and the impact is higher.

So, compared to other countries, India is more at risk.

Then, we are in the tropical region which means we have high heat in summer. We also have heat waves.

In addition to that, climate is changing. So also the weather patterns.

Nobody is free from global warming because we share one sky even if our land is different.

Climate change is real, and it is happening.

And in coming decades, in 2050 or 2100, temperature will be more, may be 1 degree, 2 degrees or 3 degrees or up to 5.5 degree.

The Earth's global average temperature has already reached 1.5°C above pre-industrial levels which the experts said would happen much later...

Yeah, 1.5 degree rise has already happened.

We never thought it would be this fast.

It means things are happening even beyond our calculations, even beyond our scientific calculations.

The pace is very accelerated.

Because of global warming, we have higher temperature. With high pollution, the ozone effect will be much higher.

In future, this is not going come down, unless we cut our emission and cut the pollutants to clean the cities or clean the re

The situation is definitely something to worry about.

Making people aware of all this is very important. Without awareness, you can't tide over the crisis.

That's why I want people to know about our study.

Feature Presentation: Ashish Narsale/Rediff