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Delhi-NCR hit by summer ozone once again: CSE analysis

An analysis carried out by the Delhi-based Center for Science and Environment found that Delhi-NCR has been hit by summer ozone once again, but levels are lower than in previous summers.

The analysis further found that New Delhi and South Delhi areas were worst affected by ground-level ozone. Central Delhi and Gurugram face a worsening crisis.

“On the eve of World Environment Day, the Centre for Science and Environment (CSE) has issued an alert on rising ozone pollution and the multi-pollutant crisis that Delhi and the National Capital Region are facing during summers. If unchecked, this can become a serious public health crisis in coming years,” the statement issued by CSE read.

The CSE noted that it has consistently issued warnings about the growing problem of ozone at the ground level in the country.

“The policy and public attention that is nearly fully drawn towards particulate pollution, has neglected mitigation of toxic gases. Inadequate monitoring, limited data and inappropriate methods of trend analysis have weakened the understanding of this growing public health hazard. Learn from the advanced economies that after controlling particulate pollution have fallen into the grip of rising NOx and ozone crisis. India should prevent this trap. But the standard practice of the Central Pollution Control Board to average out the data of all stations to determine daily AQI cannot capture the public health risk from this short-lived and hyper-localised pollutant. This underestimates the severity of the local build-up and high toxic exposures in the hotspots,” says Anumita Roychowdhury, executive director of research and advocacy at CSE.

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“Due to the very toxic nature of ground-level ozone, the national ambient air quality standard for ozone has been set for only short-term exposures (one-hour and eight-hour averages), and compliance is measured by the number of days that exceed the standards. Compliance requires that the standards are met 98 per cent of the time of the year. It may exceed the limits on two per cent of the days in a year, but not on two consecutive days of monitoring. There should not be more than eight days in a year when the ozone standard is breached, and not on two consecutive days,” says Avikal Somvanshi, senior programme manager, Urban Lab at CSE.

The CSE stated that the complex chemistry of ground-level ozone makes it a stubborn pollutant to track and mitigate.

It added that ground-level ozone is not directly emitted from any source. It is produced from complex interactions between nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide emitted from vehicles, power plants, factories, and other combustion sources and undergo cyclic reactions in the presence of sunlight to generate ground-level ozone.

VOCs can also be emitted from natural sources, such as plants. Ozone not only accumulates in cities but also drifts long distances to become a regional pollution threat, necessitating both local and regional responses. This not only affects public health but also crop production and food security.

 This highly reactive gas has serious health consequences. Those with respiratory conditions, asthma, chronic obstructive pulmonary disease, and particularly children with premature lungs and older adults are at serious risk.

This can inflame and damage airways, make lungs susceptible to infection, aggravate asthma, emphysema, and chronic bronchitis and increase the frequency of asthma attacks leading to increased hospitalisation.

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