Leaving your windows or vents open while stuck in traffic or waiting at a red light can seriously compromise the air quality inside your vehicle, according to a recent study.

Researchers at the University of Surrey in Guilford, England, found that pollution levels in vehicles stopped in these situations were 40 percent higher than in vehicles in free-flowing traffic. Keeping the vehicle windows closed and turning the fan off helped reduce pollution levels in the vehicle by 76 percent.

The study was published about two weeks before researchers at North Carolina State University warned football fans that air quality becomes significantly poorer around stadiums both before and after games. This study said this effect is a result of both tailgating and traffic congestion.

In the University of Surrey study, published in the Royal Society of Chemistry's journal "Environmental Science: Processes and Impacts," researchers drove a car along a six-kilometer round route under five ventilation settings. The route passed through 10 intersections with traffic lights, and researchers also took pollution measurements at these crossings to determine exposure to pedestrians.

Researchers found that pollutants were most likely to accumulate inside the vehicle during traffic jams when the windows were closed and the fan was on, since this type of ventilation draws in outside air. However, they also determined that there were significant levels of pollutants when vehicles were stopped at a traffic light due to emissions generated during acceleration, deceleration, and idling. These emissions were slow to disperse, and so could easily be sucked into a vehicle through the ventilation system.

The study determined that keeping the windows closed and turning the fan off was the best way to reduce exposure to pollution while stuck in traffic or waiting at a traffic light. Setting the fan to recirculate air within the vehicle and allowing more distance between the next vehicle in line were also successful in limiting interior pollutants.

Pedestrians were exposed to higher levels of pollution at traffic intersections, and researchers encouraged them to take routes that limited the number of intersections where they had to wait for a signal before crossing a road. However, vehicle occupants traveling with their windows fully open were exposed to levels of coarse pollutants up to seven times higher than pedestrians when traveling in free-flowing conditions.

In 2015, a University of Surrey team conducted similar research and found that drivers at traffic lights were exposed to up to 29 times as many harmful pollutants as those in free-flowing conditions. The researchers note that air pollution was responsible for 3.7 million premature deaths in 2012, according to the World Health Organization.

In the North Carolina State University study, researchers used stationary and mobile air monitors to measure air quality in and around the university's stadium before, during, and after each of the six home football games in 2015. The study found that there were spikes of poor air quality near large charcoal grills, older generators, and larger idling vehicles during pregame tailgating festivities.

Air quality inside the stadium was good during the game, but worsened afterward as thousands of fans left at once. Even after traffic congestion cleared and idling vehicles cleared out, the levels of fine particulate pollutants sometimes did not return to pregame levels until the previous morning.

The researchers advised that football fans who are more sensitive to poor air quality should leave before the end of the game or remain in the stadium until most of the traffic has departed.

"These findings aren't surprising, but what's unique is that we could quantify it," said Chris Frey, a NCSU College of Engineering professor. "This quantification is important. It provides information that enables people to make informed decisions about exposures."