Shanghai: Rising ozone pollution in China's cities has emerged as a major health risk, causing a rise in deaths from strokes and heart disease among vulnerable residents, according to a new study by a team of Chinese researchers.

Data from 272 Chinese cities between 2013 and 2015 showed "robust evidence" linking rising short-term ozone exposure with increased mortality from cardiovascular and heart diseases as well as strokes, according to a paper published in the Environmental Health Perspectives journal.

Ground-level ozone, also known as photochemical smog, is caused by the interaction of sunlight with nitrogen oxides (NOx) and the vast amounts of uncontrolled volatile organic compounds (VOCs) produced by burning fossil fuels or producing chemicals.

China is waging a "war on pollution" to reverse the environmental damage done by nearly four decades of untrammelled economic growth. But much of the focus has been on reducing concentrations of small airborne particles known as PM2.5, especially in winter.

Kan Haidong, director of the department of public health at Shanghai's Fudan University, said while PM2.5 is currently a bigger contributor to China's overall disease burden, ozone is already equally significant in regions like the Pearl River delta.

"Ozone has been increasing in the past several years in China," said Kan, who was involved in the study. "In contrast, PM2.5 has decreased by about 30 per cent in the past five years."

Lauri Myllyvirta, a Beijing-based campaigner with environmental group Greenpeace, said soaring ozone is partly a result of China's success in reducing PM2.5. Reuters