It is a weekend and you are taking your family to granny's house. You turn the AC on and close the windows to add a dash of comfort while traveling. But you have one problem: you are a smoker and you want a stick or two while driving.

If that situation is nothing new to you, it is high time to consider recent research from Stanford University. According to Stanford researchers, a person who smokes just two cigarettes in a car releases particulates above government safety levels.

Wayne Ott and Neil Klepeis, both of Stanford University in California, calculated over 100 air change measurements involving smoking by keeping track of a number of independent variables like car speed, fan position, air conditioning setting and whether windows were open or closed, reported the United Press International.

As such, the researchers advise people to not smoke in the car if they are heading off for a trip because it will expose their family members to those potentially harmful particulates.

"This is the most comprehensive set of measurements ever made of vehicle air change rates and smoke particulate levels in real driving conditions," said Klepeis, a consulting professor of civil and environmental engineering. "Conditions in a car with a smoker can vary widely, but in some situations we can confirm that passengers will receive an exposure to secondhand smoke that is considered unhealthful." Klepeis is the co-author of a Stanford study published online in the Journal of Exposure Science and Environmental Epidemiology.

The study follows a similar effort published in June by Klepeis and fellow researchers about the dangers of second-hand smoke in outdoor settings. That study was almost immediately cited in debates about the dangers of outdoor smoking, said Ott, also a consulting professor of civil and environmental engineering.

According to the research, in a car with the windows up and the air conditioning on maximum, after just two cigarettes, the exposure of smoke to a passenger would go beyond the U.S. government levels by 20 percent. Even with a car's windows open, smoke particle concentrations were higher than levels measured in California bars before a state smoking ban enacted in the 1990s, the research added.

"In other words, being in the car with a smoker under these conditions gives such a huge amount of particulates that you'll exceed what would be considered a safe level of exposure," Klepeis explained. "If more people become aware that smoking in their car could lead to harmful toxic exposures for their family and friends, they may decide to ban smoking in their cars - at least while others are present."

Klepeis and Ott collaborated with Stanford statistics and earth sciences Professor Paul Switzer on the paper, which followed an article they published in June on secondhand smoke exposure in outdoor café settings. In both the café and the car studies, the team sought to measure smoke particles of less than 0.0001 inch (2.5 millionths of a meter) in diameter, the Science Daily reported.

These particles are deemed a health risk by the EPA because they can penetrate deep into lung tissue when inhaled, the report noted. The level the agency considers unhealthy is 35 millionths of a gram per cubic meter (35 µg/m3), averaged over 24 hours.

"That paper, the first of its kind, almost immediately began to be cited in policy debates about regulating outdoor smoking," Ott said. "Our hope is that this research can lend rigorously acquired and analyzed, objective scientific information to this debate."

You might be considering the engines, distributor cap, brakes but fall short on precautions that involve your self. Think about it.