TUESDAY, Oct. 16 (HealthDay News) -- Smoking in cars produces levels of harmful particulate pollutants that are far above World Health Organization indoor air standards and likely pose a threat to children's health, a new study reveals.

Dangerous levels of particulate air pollution occur even when the windows are open or the air conditioning is on, according to the findings released Oct. 15 in the journal Tobacco Control.

For the study, researchers in the United Kingdom measured fine particulate matter every minute in the rear passenger seat of cars driven by 14 smokers and three nonsmokers. The journeys lasted from five to 70 minutes, with an average duration of 27 minutes. Of the 83 journeys, 34 were smoke-free.

Particulate matter levels averaged 7.4 micrograms per cubic meter of air (mcg/m3) during smoke-free drives, but were around 11 times as high (85 mcg/m3) during drives where smoking occurred. Particulate matter levels were strongly associated with the number of cigarettes smoked, with average levels peaking at 385 mcg/m3. The highest recorded level was 880 mcg/m3.

Even though smokers usually opened the car windows to provide ventilation, at some point during the drives where smoking occurred, particulate matter levels were still higher than the safe limit of 25 mcg/m3 recommended by the World Health Organization, the investigators found.

Children's health problems, including sudden infant death, middle ear disease, wheeze and asthma have all been linked to secondhand smoke exposure, the researchers noted in a journal news release.

"Children are likely to be at greater risk from [secondhand smoke] exposure due to their faster breathing rates, less developed immune system and their inability to move away from the source in many home and car settings," wrote Dr. Sean Semple, of the Scottish Centre for Indoor Air at the University of Aberdeen in Scotland, and colleagues.

More information

The U.S. Centers for Disease Control and Prevention has more about secondhand smoke exposure.