Ground-level ozone on the rise

Increasing pollutant levels could cause major food crisis, says Royal Society.

Vehicle exhausts can drive up low-level ozone. Credit: Punchstock

The concentration of ozone at ground level is continuing to rise despite regulations aimed at controlling the gas, according to a study from the Royal Society, the UK national academy of science. The pollutant's impact on human health and crop yields is also worse than previously through, the study warns.

Background levels of ozone have increased by about 2 parts per billion (p.p.b.) per decade since the 1980s, rising to damaging levels of 35–40 p.p.b. in most of the industrialised countries of the world.

"Once thought to be a local- or regional-scale issue, ground-level ozone has emerged as a global pollutant," the report says. A global agreement to control the growth in background ozone is now needed to avoid potential threats to global food security and increasing numbers of human deaths, it concludes.

Friend and foe

Ozone is a natural constituent of the atmosphere. In the stratosphere it serves as a protective sunscreen that shields the Earth from high levels of ultraviolet radiation from the Sun.

But ozone at ground level is a noxious pollutant. Ground-level ozone is formed by sunlight-driven chemical reactions between volatile organic compounds (such as fuel hydrocarbons), and nitrogen oxides that largely come from vehicle exhausts.

The World Health Organisation has ruled that ozone causes effects on human health at levels above 50 p.p.b.. But the Royal Society's study says that impacts have been seen at levels of 35 p.p.b., and according to the European Environment Agency, over 21,000 premature deaths each year are associated with ozone in the European Union.

Impacts on vegetation are thought to generally occur at 40 p.p.b.. In the European Union in 2000, an estimated €6.7 billion (US$9 billion) was lost due to ozone impacts on arable crops, the study says.

Crop shock

The study reviewed the most recent data available, and carried out new modelling work, to assess possible changes in ozone from 2000 until 2050.

If all existing regulations were adhered to, ozone concentrations would fall by up to 15 p.p.b. in the developed world by 2050. But in the developing world, where few legislative controls are in place, ozone levels would increase by about 3 p.p.b. by 2050.

Peter Cox, a climate scientist at the University of Exeter, UK, and one of the authors of the study says, "We found that ozone will have a significant impact on human health and crop yields, which is especially important as we try to figure out how to feed the world."

Stephen Long, a crop scientist at the University of Illinois at Urbana-Champaign, welcomed the report. "Overall it is excellent. It highlights, more clearly than in previous studies, that ozone can cause major problems. We knew that it could affect health, but the report brings out the effects on vegetation and crops," he says.

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Royal Society report

World Health Organisation