Polluting gases are killing more than 1,500 Britons a year, the UK's leading science body warned yesterday.
A Royal Society report highlighted the dangers of ground-level ozone caused by traffic fumes and industrial emissions.
In the high atmosphere, ozone protects us from ultraviolet rays, but at ground level it damages the lungs, causes chest and breathing problems and has been linked to bronchitis, heart attack and early death.
The Royal Society said the pollutant is already present in quantities that are harming health and farming, and levels are rising by 6 per cent a decade.
In 2003, 1,582 deaths in the UK were attributed to the gas. The report predicts this will rise to around 2,391 deaths a year by 2020 as a result of increased pollution and climate change.
Ground ozone is created when sunlight breaks down pollutants in the air with levels peaking on sunny and stagnant days.
Most ozone in the UK travels here from outside of Europe on air currents.
The Royal Society called for an international response to the problem.