(CNN) Breathing is the most basic function of our bodies, we do it all day, every day.
So it's hard to think of an environmental issue which is less discriminating than air pollution. It affects us all.
As Andrew Grieve, air quality analyst from King's College London says, the effect is cumulative, from your first breath to your last breath. Little kids, older people, people who have respiratory conditions. Everyone is exposed.
And yet by the same token because of its huge impact, any reduction, however small, benefits us all.
The World Health Organisation estimates that air pollution is responsible for up to seven million deaths each year. That means one in eight deaths worldwide can be attributed to contaminated air.
And urban areas are some of the worst affected.
A report from King's College London has found that around 9,500 people die each year in the UK capital because of the levels of nitrogen dioxide and fine particulate matter.
One of the main contributors is traffic. It's responsible for up to two thirds of urban pollution, says Grieve. So what can we do about it?
Clean fuels mean cleaner skies, and in an ideal world we'd all use electric vehicles.
But there is another way we could improve our city air, according to Martin Williams, from the Environmental Research Group at King's College London, who advises the World Health Organisation.
Contrary to what we've learned over the last few decades, he says, we need to switch our cars back to petrol from diesel.
"Diesels 20 years ago were seen to be a lot more fuel efficient than petrol cars and so they were encouraged. It now seems in retrospect that they haven't worked."
Diesel vehicles have been championed for being more efficient, giving more miles to the gallon, and therefore creating fewer carbon emissions. They were seen as a way to help countries make reductions in their greenhouse gases.
In fact the International Council on Clean Transportation has shown that modern diesel cars are on average seven times over the European limit for nitrogen oxides -- the poisonous gases that are released when fuel is burnt. And they are also worse for particulate pollution -- tiny specks of contamination which can harm the lungs and cause respiratory illness.
Diesel vehicles have been a game-changer for air quality, says Grieve: "It turns out that they emit far more nitrogen dioxide and particulates than petrol cars. Ten or 20 times more. And that has been a real problem for air pollution in cities."
These are lessons which need to be shared, says Williams. In China, where the rising middle classes are putting more cars on the road, people should be cautious.
"The main change has been buying cars instead of bicycles in places like Beijing. But the good thing about Beijing is that most of their vehicle fleet is petrol. 95% of cars in Beijing are petrol cars, very few diesel. And China needs to learn from the West's bad experiences and keep it that way."
There are steps we can take as individuals too. We can drive more responsibly, says Williams.
"Switch off your engine when you're at a long traffic light, and be careful with your right foot.
And of course choose to walk and cycle rather than drive in the first place."