Derry in Lutyens is One of the most iconic neighborhoods of the Indian capital. Home to the country’s parliament, numerous embassies and a lush 90-acre Mughal-era park, it’s an architectural haven linked by tree-lined streets and roundabouts with miniature gardens. Yet, despite being one of the city’s most refined areas, this clean, green neighborhood hides something sinister. It’s a hotspot for a dangerous and neglected air pollutant: ozone.
India is no stranger to pollution, with air quality in many Indian cities among the worst in the world. Every winter, New Delhi is shrouded in smog for several days. But much of the discussion about air pollution and policies to mitigate it has focused on particulate matter: PM2.5 and PM10 — tiny particles or droplets just a few microns in diameter. Yet scientists are increasingly sounding the alarm about surface ozone. It is a secondary pollutant that is not released from any source and forms naturally when nitrogen oxides and volatile organic compounds (such as benzene or methane in gasoline) react in heat and sunlight. That makes ozone a particularly ugly modern-day threat — a problem that arises where pollution and climate change go hand in hand.
“Even one hour of exposure can give you very bad health outcomes,” says Avikal Somvanshi, a researcher at the Center for Science and the Environment in New Delhi. While ozone is beneficial in the upper atmosphere, where it absorbs ultraviolet radiation, at the Earth’s surface, it Concentrations may be fatal. Data on its effects are incomplete, but a 2022 study estimated that ozone killed more than 400,000 people worldwide in 2019, an increase of 46% since 2000. According to the 2020 State of Global Air report, India has seen the largest increase in ozone deaths over the past decade.
Ozone wreaks havoc on the respiratory tract. The EPA warns that the gas can “inflame and damage the airways” and “aggravate lung diseases such as asthma.” It does this by affecting cilia, the tiny hair-like structures that line the airways to help protect them, explains Karthik Balajee, a clinician and community medicine specialist in Karaikal, India. “We are more susceptible to respiratory infections” after exposure to ozone, he said, adding that inhaling ozone also affects lung capacity. Studies have shown that long-term exposure can increase the risk of chronic obstructive pulmonary disease, a lung disease that makes breathing difficult, and increase the risk of death from other cardiovascular or respiratory diseases. Even a short exposure can land you in the emergency room. “In the day or two after the ozone peak, there was an increase in hospital admissions for respiratory problems,” Balajee said.
Ozone peaks in Delhi and other major Indian cities throughout the year, especially during summer heat waves that are becoming more common due to climate change. The World Health Organization says exposure to ozone in the air should not exceed 50 parts per billion in an eight-hour period; India’s air quality standards state that it should not exceed the WHO limit for 8 days a year and two consecutive days. limit. But an analysis by Somvanshi and his colleagues found that between March and May this year, Delhi and surrounding areas had exceeded ozone standards on 87 days. They’ve seen similar results over the past three summers. Although the number of monitoring stations recording ozone threshold violations this year is smaller than in previous years, the duration of the violations has been longer. “We’re not even fully compliant yet,” Somvanshi said.
Part of the problem is ozone’s complex relationship with other air pollutants. Ozone formation is a cyclic reaction, meaning that ozone is created after a reaction between air pollutants, and when it reacts again with airborne pollutants such as nitrogen oxides, the ozone is converted back to oxygen. But if these pollutants are not present after ozone is formed, it persists. That’s why ozone levels soared during India’s Covid-19 lockdown in the summer of 2020, when traffic came to a sudden stop — without producing the air pollutants needed to convert it back into oxygen. This is also why ozone is often found in greener neighborhoods like Delhi in Lutyens – because the air is cleaner there and no ozone-destroying reactions take place.
