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August 25, 2009

Secondhand Smoke Levels Higher in Cars than in Bars or Restaurants

The concentrations of secondhand smoke are significantly higher in cars than concentrations generally measured in bars, restaurants and other public places that allow smoking, according to a study by researchers at the Johns Hopkins Bloomberg School of Public Health. The study is among the first to measure smoking in cars under real-world driving conditions and is published on August 24, ahead of print, in Tobacco Control.

For the study, researchers monitored the air in the cars of 17 smokers and 5 non-smokers. “Two air monitors were placed in each car for a 24- hour period,” said study author Miranda Jones, a master’s student with Bloomberg School of Public Health who conducted the study as part of her Diversity Summer Internship Program. The cars were driven as the participants commuted to and from work for at least 30 minutes. The median air concentrations measured were 9.6 µg/m3 (micrograms per cubic meter.) After 1 to 3 cigarettes, airborne concentrations of nicotine were 72 times higher in cars with smoking compared to smoke-free cars. After adjusting for factors such as air conditioner use, vehicle size, window opening and sampling time, there was a 1.96-fold increase in air nicotine concentrations per cigarette smoked.

Study participants were also surveyed on their knowledge and attitudes regarding health risks of secondhand smoking and relevant regulations/legislation. “Fifty-three percent of the smokers surveyed said that being unable to smoke in the car would help them to quit smoking altogether,” said Jones. Ninety-three percent of smokers agreed that motor vehicles should be smoke-free on a voluntary basis, but only 7 percent of smokers agreed vehicles should be smoke-free by regulation. All of the study’s participants--smokers and non-smokers--agreed that smoking in the car posed a health risk to passengers.

“Involuntary exposure to secondhand smoke accounts for thousands of cases of respiratory, cardiovascular and cancer deaths in the U.S. every year. While some states have smoke-free regulations, the high air nicotine concentrations measured in this study support the urgent need for smoke-free education campaigns and legislative measures banning smoking in motor vehicles when passengers, especially children, are present,” said study author Ana Navas-Acien, MD, MPH, assistant professor with Bloomberg School’s Department of Environmental Health Sciences and the Institute for Global Tobacco Control.

“There is no known safe level of exposure to second hand smoke. Because smoking in cars can contaminate the entire vehicle, exposure to hazardous components of secondhand smoke can occur long after smoking has stopped,” said co-author Patrick Breysse, PhD, MHS, professor in the Bloomberg School’s Department of Environmental Health Sciences.

Jie Yuan also contributed to “Secondhand tobacco smoke concentrations in motor vehicles: a pilot study.”

The research was funded by a Clinical Investigator Award from the Flight Attendant Medical Research Institute (FAMRI).

Media contact for Johns Hopkins Bloomberg School of Public Health: Tim Parsons at 410-955-7619 or