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A commonly circulated online item about the dangers of benzene supposedly emitted by automobile components has been widely misunderstood: Many readers have come away from viewing this piece with the impression that it warns drivers not to use their cars' air conditioning because the A/C system itself is producing benzene, but what the article actually cautions against is the practice of turning on the air conditioning immediately upon entering an automobile. Motorists should instead, it says, roll down their windows in order to allow accumulated benzene fumes (allegedly emitted by other components, such as dashboards and upholstery) to vent from the car first before re-closing the windows and turning on the A/C. How much truth is there to this warning? Some evidence suggests an association between exposure to benzene and an excess risk of leukemia, as noted by the American Cancer Society (ACS): But do automobiles really produce potentially cancer-causing levels of benzene? No studies have yet documented that claim to be true. A 2001 study of commuter exposure (in both cars and buses) in Korean urban areas found some relationship between automobile use and exposure to benzene, but its observations differed from the warning quoted above in some significant areas: The study found that exposure levels were significantly higher during the winter months, which suggests that automobile air conditioning use is not a major factor in benzene exposure. The Korean study itself did not establish a connection between commuter exposure to benzene and the onset of cancer. A 2007 German study on Toxicity of Parked Motor Vehicle Indoor Air which specifically tested the health effects of emissions from one new and one three-year-old vehicle exposed to parked in sunshine conditions found no apparent health hazard of parked motor vehicle indoor air: (The German study also found the total amount of volatile organic compounds in a new car to be one-tenth the level claimed in the e-mail for benzene alone.) The ACS similarly noted of this warning that: The e-mail did get one thing right, though: Upon returning to a closed car on warm days, you should optimally open the windows for a minute or so rather than leaving them closed and immediately turning on the air conditioning. The reason has nothing to do with benzene levels, however; rather, it's because when a car is parked in the sun with its windows rolled up, that condition can create a greenhouse effect which causes the interior of the vehicle to warm up to a temperature considerably higher than that of the outside air. Opening the windows for a few moments allows for the exchange of hot air from inside the vehicle with cooler air outside, speeding up the process of cooling off the car more than air conditioning alone would. Sources: Benzene and Cancer Risk. https://www.cancer.org/healthy/cancer-causes/chemicals/benzene.html. Accessed 20 June 2022. Buters, Jeroen T. M., et al. Toxicity of Parked Motor Vehicle Indoor Air. Environmental Science & Technology, vol. 41, no. 7, Apr. 2007, pp. 2622–29. DOI.org (Crossref), https://doi.org/10.1021/es0617901. Does Sunscreen Contain Harmful Chemicals? Snopes.Com, https://www.snopes.com/fact-check/sunscreen-chemicals-harmful/. Accessed 20 June 2022.
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