Cars are no protection from polluted air

March 9, 2018 - 06:20

Winter cold raises questions about what the combination of cold air and traffic means for air quality. Norwegian traffic researchers respond.

Being inside an automobile can protect you from some air pollution, but not all. (Illustration photo: Berit Roald / NTB scanpix)

If you live in a city, politicians generally want you to walk, cycle, or take public transport instead of driving — it’s good for the environment.

But is it good for you? What kind of risks do you run by being exposed to polluted air?

International research shows that your exposure to potentially dangerous nitrogen dioxide (NO2) from car traffic is the same inside a car as outside a car. Where a car does offer some protection is with particulate matter and a few other contaminants, which can be partialy filtered by the car's ventilation system.

But whether you’re on foot or in your car, you can’t escape NO2.

Researcher Ingrid Sundvor at the Norwegian Institute of Transport Economics (TØI) has examined current international research on traffic air pollution at the request of the Norwegian Environment Agency.

Her charge was to determine what kinds of risks a person faces from breathing air pollution from traffic if traveling on foot, by bike, on public transport or in an automobile.

Where and when means a lot

Sundvor says where you are in traffic and how you travel can have a lot to say about how much air pollution you’re exposed to.

The timing of your travel can also determine the amount the air pollution you encounter. And it's not always that rush hour traffic is bad. Sometimes weather conditions play a far more important role.

Road transport is one of the largest sources of local air pollution in Norway.

If you're inside a car, you'll get some protection from the filters in your ventilation system. The ventilation system can help protect you from particulate matter and dust. But that system can’t protect you from NO2, which is a gas. That means you are equally at risk of breathing NO2 while in your car as you are out on your bike, international research shows.

Bumper-to-bumper traffic or tailgating brings you closer to the exhaust from the car in front of you, which in turn affects NO2 levels inside your own car.

NO2 was the substance of concern in the scandal where Volkswagen cheated on emissions testing results for its diesel vehicles. Exposure to the pollutant can weaken lung function and worsen asthma and bronchitis, according to the Norwegian Institute of Public Health.

Keep away from traffic
  • Research shows that you can avoid some pollution by keeping well away from traffic and individual cars.
  • If you ride a bike, you will be exposed to less pollution if you stick to separate bike paths rather than cycling along major roads. Clearly, routes with less traffic are better than roads or routes with a lot of traffic.
  • If you are walking or riding a bike, city streets with tall buildings on both sides can increase air pollution concentrations. In fact, it may be better to walk or ride along open roads with more traffic than to travel narrow streets with less traffic.
  • In Norway, however, a major source of road dust can be roads with lots of traffic and where cars can travel at high speed, especially if many of the cars have studded snow tires. Fortunately, these types of roads are most likely to be outside of city centres. International research is less clear as to what’s the best choice when it comes to road dust. There may be far more particulate matter and dust along open roads in the countryside compared to narrow city streets.
Keep exercising

Not surprisingly, if you exercise to the point where you’re breathing heavily, you risk exposing yourself to more air pollution.

However, the majority of the studies on this issue concur that the health benefits of being physically active are so great that for most people, it will always pay off to exercise.

Ingrid Sundvor believes that this is generally true everywhere in Norway. However, this may not be true for people who have pulmonary or other health problems that make them more vulnerable to air pollution. Unfortunately, there is not enough in the research literature to come to any conclusions one way or another, Sundvor says.

Pollution in the subway

Even if you get away from the street, you may be exposed to pollution in the underground or subways. International research documents high levels of dust and particulate matter in subways around the world.

The dust in subways has a different chemical composition than in outdoor air. Instead of the road dust that gets kicked up by cars, this dust comes from wear on the train’s brakes, rails and wheels. Consequently, it contains a lot of metal particles, which means if you travel a lot by subway, your exposure to metal dust is probably much higher than if you walk outside.

Researchers suggest that those who build and operate subways should be more aware of the problem. One solution is to incorporate changes into the subway car’s different mechanical parts, particularly the braking system.


Read the Norwegian version of this article at