Prof Kevin McConway, a statistician at the Open University said, based on the findings, if Newcastle were to halve its current particulate air pollution level it would lead to two or three fewer low weight babies out of the total 3, 500 or so born in the city each year.

BBC: Traffic fumes linked to lower birth weight

The level of air pollution caused by vehicles across Sheffield is being monitored at sites across the city.

BBC: Traffic pollution tested across Sheffield

Outdoor air pollution is at its lowest level in 30 years.

CNN: Challenges ahead for a changing Earth

Earlier this year air pollution in London hit its highest level since 2003 according to official figures.

BBC: Boris Johnson sticks by gluing pollution to roads

Environmental health officers from Blaenau Gwent council told the meeting that monitoring suggested air pollution was not at a critical level, but this would continue.

BBC: Anger as waste fire in Nantyglo burns for 10 days

But the traffic increase has slowed progress in reducing emissions further, and people in many areas still suffer from nitrogen-related air pollution, including small particulates that get sucked deep into the lungs, and ground-level ozone - a strongly irritant gas formed by the action of sunlight on reactive nitrogen.

BBC: Nitrogen pollution 'costs EU up to ?280bn a year'

The ALA analyzed particle pollution levels two ways: short-term particle pollution, or high spikes in the level of soot and other toxins in the air that last a few hours to a few weeks, and year-round particle pollution, or the annual average of particle pollution levels.

FORBES: List: America's Most Polluted Cities