A recent analysis by the Centre for Science and Environment (CSE) has revealed that major Indian cities, including Kolkata, Bengaluru, Mumbai, Hyderabad, and Chennai, experienced high concentrations of ground-level ozone pollution this summer. This is a growing concern because ozone is a highly reactive gas that can be harmful even with short-term exposure.

Ground-level ozone, unlike particulate matter, is not directly emitted from any source. It is formed through complex chemical reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide (CO). These pollutants are emitted by vehicles, power plants, industries, and other combustion sources. The chemical reactions occur in the presence of sunlight, leading to the formation of ozone at ground level.

Several factors contribute to the high concentration of ozone in these mega cities. Vehicular emissions are a major source of NOx and VOCs. Industrial emissions from factories and power plants also play a significant role. Additionally, construction activities, waste burning, and even domestic activities like painting can release ozone precursors. Hot weather conditions exacerbate the problem, as higher temperatures and stronger sunlight accelerate the chemical reactions that form ozone. Furthermore, dust storms can increase PM10 levels, which indirectly contribute to ozone formation.

The health impacts of ground-level ozone pollution are wide-ranging. Short-term exposure can cause respiratory problems such as chest pain, coughing, bronchitis, and asthma. It can also inflame and damage the lining of the lungs, leading to long-term health issues. Studies have linked ozone exposure to increased hospital admissions for Chronic Obstructive Pulmonary Diseases (COPD) and a higher risk of cardiovascular and respiratory deaths. Children are particularly vulnerable, with increased ozone concentrations associated with more hospital admissions and unscheduled asthma medication use.

Addressing ozone pollution requires a multi-pronged approach. Anumita Roychowdhury, executive director at the CSE, emphasized the need for improved monitoring and mitigation strategies. She also noted the current policy focus must be expanded to include a reduction in local exposures to this toxic gas. Sharanjeet Kaur, deputy programme manager at CSE's Urban Lab, highlighted that inadequate monitoring, limited data, and inadequate methods of trend analysis have weakened the understanding of this growing public health hazard across India. More aggressive reduction of gases from vehicles, industries, waste, and solid fuel burning is essential to control ozone formation in the atmosphere. Some steps that can be taken are enforcing stricter emission standards for vehicles and industries, promoting the use of cleaner fuels, improving public transportation, and managing construction and demolition activities to minimize dust emissions.