Air pollution could be responsible for hundreds of car accidents a year, according to the London School of Economics.
A study looking a five years of data showed that when levels of nitrogen dioxide (NO2) rise just one microgramme per cubic metre, the number of collisions rises by two per cent.
Instead, they believe that the toxic air impairs driver fitness, while watery eyes and an itchy nose could also be distracting for motorists.
A recent study found that air pollution inside a car can be more than double that on the outside because the NO2 builds up in a small space.
Lead researcher Lutz Sager of the Grantham Research Institute on Climate Change and the Environment at the LSE said: “Although it has already been shown that air pollution adversely affects human health and the ability to carry out mental tasks, this is the first published study that assesses the impact on road safety.
“The analysis identifies a causal effect of air pollution on road accidents, but I can only speculate about the cause of the link.
“My main theory is that air pollution impairs drivers’ fitness. However, other explanations are possible such as air pollution causing physical distractions, perhaps an itching nose, or limiting visibility.”