It has been found by the Perth researchers that only two people smoking in outside areas can increase the risk of developing respiratory problems in non-smokers.

Air quality tests at 28 pubs and cafes across Perth have been carried out by the Council on Smoking and Health and Curtin University, the University of WA.

In order to determine the health risk to non-smokers, a particle monitor was used by the researchers to measure the number of microscopic air pollutants, which are of the same size as the tobacco smoke particles present in the air.

According to the Curtin University Professor of Health Policy, Mike Daube, even in well-ventilated areas, people are at risk of developing health problems, due to passive smoking.

After conducting the test, it was found that smoke particle concentrations were about four micrograms per cubic meter of air, when no person was smoking tobacco and this number increased to 14.25 micrograms per cubic meter of air, when only one person started smoking.

It was detected that when the number of smoking people increased, the amount of second-hand smoke was also increased.

According to Curtin researcher Julia Stafford, these findings have supported the legislation, which restrict smoking in alfresco areas and it will come into effect in September this year.

"This research supports smoking bans in areas where people may spend extended periods of time, such as outdoor eating and drinking venues", she said.