POLLUTION levels in an average smoker's home in Glasgow were seven times worse than levels recorded near the M8, a study has found.

Air quality in homes was measured and compared to city centre air pollution on the same day to look at PM2.5 levels - the fine particles in the air that cause harm.

The study found toxicity ­levels in smokers' homes were seven times higher than in Townhead, near the M8.

It also found that it takes three hours and 47 minutes for the chemicals in the second-hand smoke to return to background levels in a home after the last cigarette was put out.

Scotland became the first country in the world to set a target to reduce the proportion of children exposed to second-hand smoke in the home from 12% to 6% by 2020.

The Scottish Government has also opened the door to a possible new law that would ban smoking in cars with children on board.

Dr Sean Semple, of Aberdeen University, who led the study, said: "Parents naturally want to protect the health of their children from smoke and often think that opening a window or smoking at the back door is enough to clear the air.

"It isn't - and the only way to keep levels of particle pollution down is to take your smoking right outside.

"The only way to truly ensure your family isn't breathing in the harmful chemicals from cigarette smoke is to take smoking right outside of the home, shutting the door behind you."

Michael Matheson, Minister for Public Health, said: "The effects of second-hand smoke can have serious consequences for a child's health, and as these findings show, the harmful chemicals in second-hand smoke can linger for hours.

"Smoking at an open door or window isn't enough. To protect children, smoking needs to be taken right outside of the home."

caroline.wilson@eveningtimes.co.uk