As India grapples with the scorching heat of its summers, there is a less visible but equally menacing threat in the air: surface ozone pollution. While the nation’s bustling cities and industries have long been associated with the haze of particulate matter, another form of ground-level pollution, ozone, has been silently affecting the environment.
India is unfortunately home to some of the most polluted cities in the world, and while particulate matter often dominates headlines, the problem of ozone pollution has been lurking in the shadows.
According to the Central Pollution Control Board’s (CPCB) Air Quality Index, ozone levels in parts of Delhi and other major cities have been on the rise. Recent data shows that ozone levels spike to hazardous levels as temperatures increase.
However, national air quality standards and plans have mainly focused on particulate matter (PM2.5) alone. The National Clean Air Programme (NCAP), India’s primary initiative against air pollution launched in 2019, has primarily targeted PM2.5 particles.
These minuscule particles, measuring less than 2.5 micrometres in diameter, can infiltrate our lungs, posing serious health risks. However, this exclusive focus on particulate matter may be overshadowing other equally pressing threats.
R Suresh, an expert at The Energy and Resources Institute, explained that unlike some other pollutants, ozone is not directly emitted from any single source. Instead, it forms when various compounds, including nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO), and methane (CH4), react in the presence of sunlight and high temperatures.
This reaction is influenced by the relative concentrations of VOCs and NOx, creating what scientists refer to as “ozone isopleths.” Vehicle exhaust, fossil fuel combustion, gasoline vapors, chemical solvents, and natural sources release NOx and VOCs into the air, which are essential ingredients for ozone formation.
At optimal temperatures and under intense ultraviolet radiation, these hydrocarbons undergo complex photochemical reactions, resulting in the buildup of ozone pollution that can persist late into the night. Of particular concern are NOx emissions from transportation, as diesel and petrol vehicles are the largest source of ozone-forming NOx in urban India. As NOx emissions have not decreased proportionally to PM2.5, ozone levels continue to rise each summer.
China provides a cautionary example in this regard. Vigorous emission controls reduced PM2.5 concentrations significantly but led to a surge in ozone levels. Data from 2017 to 2019 in China’s Northern Central Plains indicates a 15 percent decrease in PM2.5, potentially driving the continued anthropogenic increase in ozone, coupled with unmitigated VOC emissions. This trajectory in India underscores the need for a holistic approach to air quality management.
Inhaling ozone can have severe consequences for human health, causing breathing problems, asthma attacks, lung inflammation, coughing, chest pain, and throat irritation. It reduces lung function and harms the respiratory system. Numerous studies conducted globally over decades have linked both short and long-term ozone exposure to increased hospitalizations and premature deaths from respiratory and cardiovascular causes.
Ozone may also weaken the immune system, making individuals more susceptible to respiratory infections—a significant concern in the post-COVID era as India continues to battle the pandemic. A study by scientists from the University of Leeds, UK, suggests that by 2050, projections indicate that 1.6 million deaths in India could be attributed to ozone pollution.
The consequences of ozone pollution extend beyond human health, impacting crops and food security. Ozone can damage crops, reducing yields and affecting food security. It enters plant leaves through tiny pores called stomata, damaging plant tissues, accelerating aging, slowing photosynthesis, stunting growth, and ultimately reducing crop yields. A study published in the American Geophysical Union’s Journal highlighted that current ozone-induced damage to wheat and rice in India is sufficient to feed roughly 35 percent of the nation’s poor.
Models suggest that ozone pollution could lead to wheat production losses of 26-35 million metric tonnes globally. Local studies conducted at the Indian Agricultural Research Institute and other institutes show that ozone exposure during peak crop growth results in 10-15 percent yield loss for grains like rice, wheat, and soybean across parts of India.
With extreme heat, erratic rainfall, and other climate change effects already impacting farm incomes, unchecked ozone pollution poses a significant risk to India’s agriculture sector and its self-sufficiency goals.
Ozone is not only toxic to humans and plants but also degrades materials. As a potent oxidizing agent, it accelerates corrosion of metals, degrades polymers, and erodes building materials over time. Studies estimate that it causes an additional 3-5 percent economic loss due to the reduced service life of rubber, textiles, dyes, and paints. India’s cherished monuments, like the Taj Mahal, face increased degradation from rising ozone pollution in urban centers like Agra. The economic toll from ozone’s infrastructure damage will only increase over time if left unaddressed.