Although ozone high in the atmosphere is vital for our survival, shielding us from harmful UV radiation, at ground level it is very harmful and has been linked to respiratory conditions, heart attacks and even cancer.

Ozone forms when sunlight interacts with gases such as methane, nitrogen oxides and carbon monoxide, emitted by ships, cars and power plants.

To investigate its effect on human health, Susan Anenberg of the University of North Carolina, Chapel Hill, and her colleagues used computer simulations to estimate how much ozone people in North America, the European Union, and south and east Asia would breathe if each region cut emissions of ozone triggers by a fifth.

The researchers then plugged this data into a public health model to estimate how many lives would be saved in each region thanks to such a drop in ozone levels.

They found that some 21,800 ozone-linked deaths a year could be avoided in the northern hemisphere alone.