TOXIC gases blown across the Atlantic from America are pushing British cities over the legal limit for air pollution and damaging people’s health, an official study shows.

The study, by the Natural Environment Research Council (Nerc), suggests that up to 2,000 tons of ozone, originating in cities such as Chicago, Detroit and New York, are hitting Britain each day.

The American ozone usually boosts British levels by 20%-30%, sometimes rising to 40%, often pushing them beyond the safe limit of 50 parts per billion (ppb) set by the World Health Organisation.

Ozone is one of the most toxic of air pollutants, with even tiny concentrations causing asthma, bronchitis and other respiratory problems.

Scientists blame it for up to 800 of the 2,000 extra deaths caused by the 2003 heatwave, when ozone levels in Britain soared to more than 90ppb.

Successive British governments have tried in vain to cut levels and the Nerc study sought to find the reason. “Our research shows British pollution control measures are not working because a lot of this pollution is coming from America,” said Alastair Lewis, professor of atmospheric chemistry at York University.

Washington is already under fire for rejecting efforts to curb carbon dioxide emissions, the main cause of global warming.

The findings on ozone emerged from one of the largest atmospheric chemistry experiments ever staged. The National Centre for Atmospheric Science, part of Nerc, took a leading role with agencies from America and Europe.

The results destroyed a basic assumption of atmospheric science — that urban pollutants such as ozone and carbon monoxide do not travel far. In fact, they rise into the upper atmosphere and are blown eastwards at up to 150mph by the jet stream, with Britain and Ireland the first land masses in the way of pollutants arriving from America.

The study, to be published this week in the Journal of Geophysical Research, found 15 US cities contributing to British pollution, including Boston and Washington DC. The researchers calculate that 1,000 tons of carbon monoxide are also swept across the Atlantic towards Britain each day.

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