In many ways American motorists and their passengers are exposed to less pollution than a generation or two ago. Back then cars ran dirtier—releasing more emissions, including lead from gasoline. Few cars were air-conditioned, so on hot smoggy days people drove with windows open, letting in pollutants from cars. And far more Americans were smoking then, often in their cars and with the kids in the back seat. For many of us, even 40 or 50 years later, it’s hard to forget that mix of smoke and fumes in the family car.
But today there’s more traffic, including more trucks and vans, and many people spend longer hours driving to work and during leisure time. So in-car exposure to pollution remains a problem for millions of Americans. Most don’t even realize that some pollutants are at higher levels inside their cars than outside on the road (so you needn’t feel sorry for those walkers or cyclists you see alongside the road). Or that the “new car smell” many people find appealing is caused by a witch’s brew of chemicals.
Pollutant levels are often higher inside because cars take in emissions from surrounding vehicles and recirculate them. Studies have found that as much as half of the pollutants inside test cars come from the vehicles immediately ahead, especially if those vehicles are highly polluting, such as heavy-duty diesel trucks. Levels of some pollutants and toxic compounds can be as much as 10 times higher inside vehicles than alongside the road.
In-car pollution levels depend on the amount of traffic, the age of your car, driving speed, ventilation, traffic congestion, the type of vehicles driving ahead of you, weather, and other factors. Opening or closing a car’s windows and vents can reduce some pollutants while increasing others. Using the air conditioner (set to use recirculated air, not outdoor air) can filter out most particulate matter, for instance, but keeps in volatile organic compounds, especially if vapors come in while refueling or if the engine is malfunctioning or if the pollutants originate inside the car.
The pollutants come largely from gasoline and diesel exhaust fumes and include volatile organic compounds (VOCs) such as benzene, toluene, and formaldehyde (known or suspected carcinogens), carbon monoxide (which interferes with the blood’s ability to transport oxygen), nitrogen oxides, and particulate matter (both coarse and fine particles). Many of these are especially hazardous for people with respiratory problems or heart disease. Fine particulate matter from heavy traffic can trigger heart attacks and strokes in susceptible people, usually within hours of exposure, studies have shown. But even in healthy people these compounds can affect heart rate and rhythm and other cardiovascular functions as well as increase markers for inflammation and blood clotting. Particulate matter can cause congestion, sinus and throat irritation, and chest discomfort; it can aggravate asthma. Some pollutants, such as carbon monoxide, benzene, and toluene, can also cause drowsiness, dizziness, nausea, and headaches.
Stopping at red lights in urban and suburban areas greatly increases the exposure to air pollution, according to a British study in Atmospheric Environment in 2015. Intersections with traffic signals—termed “pollution hot spots”—had up to 29 times higher concentrations of harmful particulate matter than open roads. And though drivers spent just 2 percent of their time passing through intersections, this accounted for 25 percent of the air pollutants they inhaled along the way. Air pollution levels are high at intersections with traffic lights because drivers decelerate, idle, and accelerate there. The same thing happens when cars idle while waiting at gas stations or at drive-through service windows at restaurants.
In a 2016 study in Environmental Science: Processes and Impacts, the same British researchers found that pollution inside cars that are stuck in heavy traffic is as much as 40 percent higher than when traffic is moving. In fact, the level of pollution was seven times higher inside cars that were stuck in traffic if the windows were open, compared to the exposure of pedestrians standing at major intersections. Keeping the windows closed with the fan on(which brought in outside air) also significantly increased in-car pollutants.
New car smell
An array of VOCs come from materials inside the car, notably carpeting, vinyl, plastics, leather, fabrics, foam cushions, adhesives, and sealants, particularly in new cars and in hot weather (heat helps release the chemicals and in some cases causes them to break down into toxic byproducts). Deodorizers and cleaning products pollute indoor air in cars, just as they do in homes.
The airborne chemicals in new cars can vary from model to model and year to year. The nonprofit Ecology Center in Ann Arbor, Michigan, has measured chemicals inside hundreds of carmodels. Among the 300 chemicals it has identified are brominated flame retardants and polyvinyl chloride from plasticizers, which are both associated with many health problems. Some carmakers have reduced the use of toxic chemicals since 2006.
The new-car smell might take a while to dissipate, according to work from Japan’s Osaka Institute of Public Health, showing that it took some four months for high levels of VOCs (35 times the maximum health limit set in Japan) to drop below that threshold. But even up to three years later, if the car heated up on a sunny day, the levels shot back up.
How to reduce in-car pollution
- When driving in traffic, keep a safe distance from vehicles ahead of you, especially diesel trucks or obviously polluting cars. Or pull over to let such vehicles get far ahead. Keep the windows closed when in traffic and the ventilation set to recirculate, especially in tunnels.
- When stopped at traffic lights, close your car windows, and try to keep some distance from the car in front of you.
- When driving in light or no traffic, keep windows open or at least cracked to let in fresh air.
- Properly maintain your car. A poorly maintained car is more likely to pollute the air inside it as well as the air around it.
- If you have the option, choose less congested roads with fewer traffic lights, even if they take a little longer. Or try to avoid rush hour. The more traffic, the more pollutants.
- Drive in the carpool lane, when possible. Carpool lanes tend to have less traffic, so there’s less air pollution.
- Take public transportation, if it’s available. Not only will you avoid pollutants, you’ll also help reduce traffic congestion and emissions. Buses, however, can be very polluting—and the air inside them quite polluted.
- Don’t count on in-car air filtration systems. Some car dealers offer charcoal (carbon) filters on select new models. These may help reduce allergy symptoms from pollens, for instance, but they are not effective in removing fine particulates, volatile organic compounds, carbon monoxide, or other pollutants.
- If you have a new car, try to drive on less-busy roads so you can keep the windows open as much as possible for the first few months, when VOC levels are highest. Don’t park it in direct sunlight.
- Don’t use air fresheners or deodorizers in your car.
- And, of course, don’t smoke in your car (or anywhere else), and don’t travel with people who smoke.
- Keep interiors clean. Pollutants in cars can combine with dust particles, which are then inhaled.
- On long drives with several people in the car, open the window for a minute or two every 10 minutes so carbon dioxide doesn’t build up.
- Don’t use chemical cleaners. Instead, use a damp micro-fiber rag to keep the interior clean. (Dust holds onto pollutants, such as VOCs.)
- Instead of an air freshener, if you want the air to smell fresh, open the windows in an unpolluted area. If that’s not possible, make a sachet of dried flower petals, or keep an open container of baking soda in the car where it won’t tip over. (You can sprinkle the baking soda under floor mats and on the carpet, vacuuming up any residue.)
Bottom line: There’s only so much individuals can do about outdoor and in-car air pollution. The government should ensure the manufacture of cleaner, more fuel-efficient cars, as well as cleaner diesel fuel and diesel technologies. It should also ensure that emission ratings from carmakers are truthful. This is not always the case, as was seen in the recent Volkswagen emissions scandal, which made millions of diesel-powered cars seem less polluting than they are.
Also see 20 Indoor Air Pollution Tips.