Breathe Easy

A number of people have asked me about automobile fumes and whether I worry about breathing exhaust as I ride my bike to work. There seems to be a widespread assumption that cyclists are exposing themselves to high levels of pollutants by riding their bikes alongside automobiles. Contrary to popular belief, it’s motorists who are getting the worst of it.

At least two studies have shown motorists are exposed to far more pollutants than cyclists, in some cases by more than fourfold. The following figures are from a widely quoted study conducted in the Netherlands in 1995¹.

  Cyclists (µg/m3) Motorists (µg/m3)
Carbon monoxide (CO) 2670 6730
Nitrogen dioxide (NO2) 156 277
Benzene 23 138
Toluene 72 373
Xylene 46 193

A 2004 Australian study, published in the Health Promotion Journal of Australia, confirms what was found in the older Dutch study. It looked at benzene, toluene, ethylbenzene, xylene and nitrogen dioxide, and again found motorists are exposed to much higher concentrations of these pollutants than cyclists.

This seems counter-intuitive since we cyclists are out in the open air, directly exposed to tailpipes, while motorists are inside their sealed vehicles with conditioned air. But, since most automobile vent systems are not filtered or completely sealed, motorists are exposed to pollutants from the stream of cars in front of them, as well as the pollutants that leak into the passenger compartment from their own engines and fuel systems.

So while cyclists should be proud of the fact that they’re sparing the air by riding their bikes, they can also breathe easy knowing they’re sparing themselves a big dose of toxic pollutants they’d otherwise be breathing if they were riding in a car.

1. The exposure of cyclists, car drivers and pedestrians to traffic-related air-pollutants, Van Wijnen/ Verhoeff/ Henk/ Van Bruggen, 1995 (Int. Arch. Occup. Environ. Health 67: 187-193).

9 Responses to “Breathe Easy”

  • andy parmentier says:

    ..this is assuming that motorists are running on fossil fuels-other combustion systems exist. a friend told me about a proprietary 5 inert gas mixture that would run an engine indefinitely. there’s no tax base for brilliance i suppose..but mediocrity and the status quo are the tax base engine of empires.

  • janfrid says:

    I don’t see if these studies account for the fact that cyclists are generally breathing at a higher rate then drivers, taking in larger volumes of air. Sometimes considerably larger and deeper.

  • janfrid says:

    Also, there are spikes of tailpipe emissions. I often hold my breath when the light turns green and throttles open wide, or when I find myself in close proximity to diesels or motorcycles, for instance.

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  • brad says:

    While here in my city (Montréal) many of the “serious” bikers shun bikepaths because they’re populated by slower recreational or commuting riders, I remember seeing a study in the journal Science a few years back showing that bicyclists who rode in bike lanes or separate bike paths were exposed to much lower levels of pollution, especially particulates, than those who rode in traffic. I’m pretty sure the Science study also considered the issue janfrid mentions above about deeper breathing.

    Diesel exhaust is particularly risky because of all the fine particulates, which pose cardiovascular and cancer risks. The current issue of Granta magazine has an article about pathology and a quote from an English pathologist who says that pretty much all urban dwellers have large black deposits of soot in their lungs. Riding a bike in traffic behind city buses and trucks for years on end would probably make your lungs look like those of a coal miner.

  • Alan says:

    This report (PDF) from the EU quotes the Dutch study and comes to the following conclusion:

    “This study, like several others, reveals that motorists are subject to high pollution levels. Even when account is taken of effort (a cyclist breathes on average two to three times as much air as a motorist), the cyclist emerges as the victor of this comparison, especially as physical exercise strengthens the ability to resist the effects of pollution.”

    No doubt, staying away from cars is best, but if you’re forced to be in traffic, better on a bike than in a car (or even a bus).

  • Val says:

    I believe that the Austrailian study actually monitored the level of carbon monoxide in the bloodstream of the subjects, and found that physical activity accelerates the rate of expulsion of this toxic gas from the body. This means that the drivers, in addition to being exposed to greater levels of toxins, are retaining them longer.

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