PARIS: Smoking inside cars raises levels of dangerous fine-particle pollutants to many times the limit recommended by the world’s health agency, a study published last week said.

Doctors in Britain measured concentrations of fine particles in cars driven by 17 people, 14 of them smokers, using an electronic monitor on the back seat. The volunteers were asked to follow their normal smoking habits as the smoke levels in their car were monitored over three days.

A total of 104 car journeys—average time 27 minutes—took place, of which 83 were accurately logged, 49 of them being smoking journeys and 34 being smoke-free. During smoking journeys, levels of fine particles were 85 micrograms per cubic meter on average, compared to guidelines of 25 micrograms per cubic meter for indoor pollution set by the UN’s World Health Organization (WHO).

Even when the driver opened the window or turned on ventilation to remove the smoke, particulate levels were still above the WHO benchmark at some point during these journeys. The average peak during smoking trips was 385 micrograms per cubic meter, with the highest being more than 880 micrograms per cubic meter. In contrast, particulate levels during non-smoking journeys averaged only 7.4 micrograms per cubic meter.

These very small particles are considered dangerous because they can lodge deep in the lung, causing irritation.

“Children exposed to these levels of fine particulate are likely to suffer ill-health effects,” said the study led by Sean Semple of the Scottish Center for Indoor Air at the University of Aberdeen. “There are increasing numbers of countries legislating against smoking in cars and such measures may be appropriate to prevent the exposure of children to these high levels of second-hand smoke.”

The investigation appeared in the journal Tobacco Control.