In case you had any doubts, a recent study has now confirmed that sitting in traffic for prolonged periods of time is bad for your health. Led by Dr. Prashant Kumar, a group of researchers from the University of Surrey has found that adjusting your car ventilation system when stuck in traffic can affect exposure to toxic fumes by up to 76%.

The measurements were made on a 6-kilometer long route inside a car using five different ventilation settings, with the car passing through 10 different signalized traffic intersections. The study aimed to compare the effects of the different ventilation settings on the concentrations of particulate matter (PMCs) inside the car to those experienced by pedestrians crossing the intersections. The lowest exposure to pollutants came when riders closed their windows and switched off car fans at signalized traffic intersections. The study showed that drivers who were stuck in traffic lights were exposed to up to 29 times more harmful pollution particles than those driving in free flowing traffic.

The study also found that fans set to re-circulate air inside the car were better than fans that drew polluted air from outside when cars were stationary. PMC levels at traffic intersections were generally found to be higher, primarily due to the accumulation of fumes emitted when vehicles queued at red lights. Emissions in these areas took longer to disperse than emissions in areas where traffic flowed.

The research was published as part of the 2016 Emerging Investigators Issue in the Royal Society of Chemistry’s journal Environmental Science: Processes and Impacts.

In 2013, the population of the UK spent an average of one hour per day commuting in vehicles. According to the World Health Organization (WHO), outdoor air pollution is among the top ten health risks faced by humans, causing seven million deaths each year.