A cyclist on the Olympic Green in Beijing in August 2008. (Robert F. Bukaty/Associated Press)

Wearing a face mask in smog-clouded cities is a good idea, a study published Friday says, but some masks are more effective than others.

A 2008 study of 15 volunteers in Beijing, with and without masks, established that "wearing a simple inexpensive and well-tolerated face mask can provide an alternative that may lead to reduced cardiovascular morbidity and mortality" by filtering particles, the researchers said.

Beijing was chosen because it is highly polluted. The researchers, led by Jeremy Langrish from the University of Edinburgh, tested 15 healthy volunteers who walked on the city's ring road for two hours, and monitored their blood pressure and heart rates.

"Our findings would suggest that wearing a simple face mask has the potential to reduce the incidence of acute cardiovascular events in cities with high levels of air pollution, and could influence the advice given to patients with chronic cardiovascular diseases," the authors reported in the journal in Particle and Fibre Toxicology.

Dust respirators get top marks

Before the experiment, the researchers tested different masks.

"In general, those masks designed to reduce occupational exposure to dusts were more efficient than those marketed as personal protection to cyclists and pedestrians in an environmental setting," they said.

They chose the 3M Dust Respirator Model 8812, because it was efficient and comfortable to wear. It was not the best of the masks tested, having a 3.4 per cent "penetrance" figure, where a lower number is better.

But four cyclists' masks tested from 15.1 per cent to 44.9 per cent, a surgical mask was at 20 per cent and a cotton handkerchief at 72 per cent.

Dust respirators and a Teflon filter performed better than the 3M mask.