Globally, breathing polluted air is the fourth largest risk factor for an early death. Most of this health impact comes from particles that pollute the air that we breath. We know from industrial diseases that inhaling some types of particle such as asbestos or coal dust is harmful. In outdoor air, the particles that we breathe come from a wide variety of sources and it is unclear what sources cause the most harm.
In a new study, Swiss scientists collected particles from five locations that were dominated by different sources: a busy road, a courtyard in the middle of Zurich and mountain valleys. Each sample was then tested to see how much it could overwhelm the protective chemicals that act as natural defences in our lungs. The chemical composition was also measured to work out the sources of the particles in each sample, to match them to their toxicity, and to estimate how much we each breathe.
The greatest toxicity in these European samples came from sources that are poorly controlled. These include wood burning, which has been increasing because of policies on renewable energy, and dusts from the wear of tyres, brakes and roads. Controlling these would require policies that reduce traffic volumes.