What's more polluted? The air outside your car or the air inside your car?

We can all see that many cities are extremely polluted and it's clear that vehicles are responsible for much of that pollution. Nitrogen oxydes, Ozone and particulates are considered the main three pollutants that affect air quality in cities. But how bad is the air for our lungs when we talk about using a specific means of transportation? Is biking in the dirty air worse than sitting in your car? Libération, one of France's most important newspapers, has a very interesting article about just this topic. The article describes the results of a study on air quality in some urban environments based on various activites. How bad is it to travel in different urban situations and how does this affect to the air quality we breathe? Follow us after the jump to see the results from worst to best.

1. Driving your car. Of course driving is bad for your health. All these pollutants going out the end of the tailpipe mean that, well, you're breathing the exhaust gases from the vehicle in front of you. And opening your windows doesn't really work. Exhaust contains nasty gases to dissipate. The article states that a baby breathes more NOx when it is inside a car than on a stroller with a parent pushing from behind.
   
2. Railways (subway and commuter trains). Mass transit is green and usually better for the environment. But the air quality inside cars can be bad due to metallic particles that dissipate in the air when braking. This is actually becoming an issue for subway workers and those that have small business in subway stations.
   
3. Bicycles. Of course it seems obvious to think that riding a bike behind the dark diesel cloud of a bus is not very good for your lungs. In fact, riding six minutes behind a bus makes you breathe nine times as much NOx as you're supposed to breathe per year. Another reason to support segregated bicycle lanes.
   
4. Walking. Walking is the healthiest option, even more so than running. Still, if you can, ask to telecommute and you can reduce your time in the city altogether.

[Source: Libération]