What is surface ozone pollution? And why is it such a problem in India?

Rising summer temperatures in India have ushered in what has become a summer trend: surface ozone pollution. New Delhi and other major Indian cities typically see ozone levels increase in the summer. But heatwaves, which have become more common in the wake of the climate crisis, have further exacerbated the problem, Wired reports.

In early May, Gurgaon, a city in Haryana on the outskirts of Delhi, saw surface ozone levels breach permissible limits, according to the Times of India. Ozone concentrations of more than 100 micrograms were recorded across the city’s air quality monitoring stations. This is considerably above the World Health Organization (WHO) air quality guidelines of 60 micrograms and hence unsafe for those living and working in Gurgaon, a financial and technology industry hub.

Rising ozone pollution is only adding to India’s wider pollution issues, and fixing the problem is not straightforward.

Ozone is a variant of oxygen composed of three oxygen atoms. It occurs both in the Earth’s upper atmosphere and at ground level.

In the stratosphere, it forms a layer that protects us from the sun’s ultraviolet rays.

Surface ozone is formed through a reaction of gases activated by sunlight. These gases include pollutants such as nitrogen oxides (NOx) emitted by cars, fossil power plants and industry. Higher temperatures provide the activation energy for more NOx to react with other volatile compounds to form ozone.

This “bad” ground-level ozone carries serious risks to human and crop health.

Breathing ground-level ozone can cause or worsen various pulmonary health issues, ranging from chest pain and coughing to bronchitis, emphysema and asthma. It can inflame the lining of the lungs and leave the lung tissue scarred over time.

Even just an hour’s exposure to elevated ozone levels can lead to very detrimental health effects, a researcher told Wired.

Globally, there were 46% more ozone-attributable deaths in 2019 than in 2000, according to a study published in the Lancet last year. South Asia showed the highest increases in ozone exposure and ozone-attributable mortality rates.

An earlier study by the University of Leeds suggested that by 2050, more than a million deaths in India could be linked to ozone exposure if emissions of ozone’s constituents can’t be reduced.

While India is not alone in facing the ozone risk, its already poor air quality and the proliferation of heat waves is a particularly serious threat to the subcontinent and South Asia.

Ten of the top 15 most polluted cities worldwide are in India, exceeding the WHO air quality guidelines by a factor of 10. Adding to this is the country’s growing and ageing population. Not only will this upward trend mean that more people will be exposed to the risks associated with ozone, but these people will also be more vulnerable, Wired reports.

High surface ozone also has a detrimental impact on crop health, threatening India’s food safety. Ozone has been shown to reduce crop yield and seed quality across all major crop varieties grown in India. Wheat and rice are particularly sensitive to ozone.

Unlike other air pollutants, removing the sources of ozone is not as easy, because it’s part of a cyclical reaction, according to Wired. As long as the reagents are still in the air, ozone gets reconverted into oxygen. If the compounds are no longer in the air to facilitate this, ozone simply lingers. This led to a rise in ozone levels in India during the pandemic, despite a marked drop in emissions.

So, while driving down the amount of precursor gases is vital, doing so has to be managed carefully to ensure enough of them remain to neutralise the ozone that’s already in the air.

Air quality alerts could help reduce flare-ups of ozone. Local warnings could be issued to stop people from fueling their cars to avoid fuel evaporating to form some of the precursor gases for ozone. Similarly, industry could be asked to shift operations to the evening or even the night.

A good monitoring and alert infrastructure exists in Delhi, but is still limited across the country as a whole. This needs to be expanded to enable such notifications.

The World Economic Forum’s Global Risks Report 2023 shows that fighting the climate crisis and issues resulting from climate change are perceived as some of the biggest threats the world faces in the next 10 years. This includes growing air pollution and its effects on health, food and natural ecosystems.

The Forum is working with cities around the globe to help solve these and other complex issues they face as they transform to become more sustainable and resilient in the future.