Backgrounder - Tobacco Smoke Concentrations in Cars

Since the release of the 2004 OMA paper, Exposure to Second-Hand Smoke: Are We Protecting Our Kids? significant research has been undertaken and there is now more compelling evidence to present about comparative concentrations of second-hand smoke (SHS) in vehicles.

There have been numerous studies that have tested in-car SHS concentrations in virtually every conceivable smoking scenario – windows open, partially open, closed, one window partially open, vents on or off, heat, air conditioning, recirculation, the speed of the vehicle, the number of cigarettes, the smoker, etc. One study looked at 100 different air change rate measurements on four vehicles. ¹

These in-car smoking experiments have been compared with similar air quality tests in smoker’s homes, smoke-free homes, smoke-filled bars and ambient outdoor air. The findings are clear. Under all ventilation circumstances, even with windows open and the fan on high, SHS concentrations in a vehicle are greater than in any other micro-environment.

Respirable particles in SHS – Key findings:

• In 2005, The State of California’s Air Resources Board (CARB) compared a large number of studies measuring SHS particle concentrations in different environments and found that in-car concentrations, with smoking and no ventilation were up to 60 times greater than in a smoke-free home, and up to 27 times greater than in a smoker’s home.²
  
  
• The research shows that even under full ventilation, interior respirable particle concentrations were at least 13 times that of the outdoor concentration. With no ventilation, these particle concentrations reached levels as high as 300 times the outdoor particle concentration. ³
  
  
• Detailed SHS concentration studies conducted in a minivan showed that “the particle exposure for an average 5 hour automobile trip, with two cigarettes smoked per hour, would be 25 times higher than the same exposure scenario in a residence.” ⁴
  
  
• Another comparison used field measurements to compare SHS particle concentrations in a vehicle, with those in a bar (when smoking was still allowed). In-vehicle concentrations were 20-times greater than inside the bar. ⁵

Formaldehyde in SHS – Key Findings:

• The CARB also looked at Formaldehyde concentrations from cigarettes in vehicles. In the US, the recommended maximum occupational level for formaldehyde is 0.1 ppm.  In-vehicle formaldehyde concentration tests found levels could reach 0.33 ppm after only one cigarette. ⁶

Carbon Monoxide in SHS – Key findings:

• Studies have found that approximately 66 mg. of carbon monoxide (CO) are emitted per cigarette smoked. ⁷
  
  
• Testing CO concentrations in vehicles in which there was smoking found that concentrations could reach as high as 63.3 ppm with very limited circulation. ⁸ This is more that double Health Canada’s “Acceptable Short-Term Exposure Range for CO” which is a maximum one-hour average of 25 ppm. 
  
  
• Carbon monoxide in the blood, represented by carboxyhemoglobin (COHb) levels, was measured for both the active and passive smoker in a vehicle and both increased significantly. The COHb level in the non-smoker (passively breathing the smoker’s SHS) rose from 2 ppm to 9.2 ppm after the passenger had smoked 3 cigarettes. ⁹