The countdown began for the launch of one of the world's most daring attempts to combat air pollution.
Starting Monday, thousands of drivers are faced with paying a new fee to enter central London.
The goal is to stop the dirtiest vehicles in an effort to reduce illnesses and premature deaths.
The initiative comes when scientists say the impacts of air pollution are more serious than previously thought.
London Mayor Sadiq Khan told the BBC that the threat of air pollution, which is almost invisible to the naked eye, is "a public health emergency."
He added: "One of the things that bothered me is that because we can not see the particulate matter, nitrogen dioxide, poison, you do not take it seriously."
But in recent decades, research has revealed how gases such as nitrogen dioxide and tiny particles, known as particulate matter or PM, can reach the body deeply, with the danger of causing permanent damage.
The most obvious effects are in our breathing – anyone with asthma, for example, is more likely to be at risk because dirty air can cause chronic problems and also trigger an attack.
"I had to stay up one night because my chest was too bad because [of] all the polluted air, "Alfie told me, aged 10." I could not sleep and my mother had to stay awake. "
"All this polluted air can harm your lungs, it can even damage your brain, it can damage almost everything in your body," he said.
A student at Haimo Elementary School in Eltham, near the bustling South Circular Road in London, Alfie is one of the 300 children in the capital who participate in exclusive research.
The project involves each child using a special air monitoring bag, specially built by Dyson and equipped with instruments to measure nitrogen dioxide and the smallest particles, called PM2.5.
One motivation for the job is that breathing in dirty air at an early age can have lifelong implications.
Research has shown that children growing on heavily polluted streets have lower lung capacity than those in cleaner areas – an average of 5%, according to a study in London – a limitation that can not be reversed.
And air pollution can also exacerbate other respiratory diseases, including emphysema and chronic bronchitis, and lung cancer is believed to be linked as well.
Ben Barrett of King's College London, who is conducting research on backpacking, says children born in a more polluted environment face greater challenges in life.
"It is not necessarily that there is a particular illness that they develop but their body is less able to handle these challenges when they go to adolescence and into old age."
Another path to evil is opened when the smaller particles find their way into the depths of the lungs, into the alveoli, from which oxygen is transferred into the bloodstream.
It has been established that PM2.5 particles are small enough to make this transition as well, entering the cardiovascular system and circulating throughout the body.
Risks include the potential to block arteries, increasing the risk of stroke along with heart disease and heart attacks.
In addition, there is evidence that particles can reach the brain, so researchers are investigating the potential effects in conditions such as dementia.
Body of Evidence
A major Chinese study last year proposed a connection between pollution and reduced cognitive performance, while a British study published last week suggested a link to psychotic episodes in teenagers.
According to Professor Jonathan Grigg of Queen Mary University in London, a leading figure in research on the effects of air pollution on children, evidence for wide impacts is growing.
"We are absolutely certain that air pollution is associated with respiratory diseases such as asthma and cardiovascular disease with heart attacks and strokes, and in five years we will be more certain about other conditions such as dementia and obesity."
A new area of research is the search for an explanation as to why babies in the most polluted areas tend to be born more preterm and underweight than those born elsewhere.
A small study, still in progress, is investigating placentas and found black spots resembling pollution particles found in lung cells.
One of the researchers involved in the study, Norrice Liu, also from Queen Mary University, said the placenta should provide a sterile environment, so the sight of black spots was a surprise.
"We know how pollution particles look like they are in cells in other parts of the body, particularly in the lungs, and the black parts we see on the placenta have a shape and color very similar to those that make us think it could be pollution particles ".
Its presence does not cause a connection with premature birth or lower birth weight, but suggests a possible mechanism.
Fifteen young mothers have so far agreed to donate their placentas to the study, and one of them, Rachel Buswell, told me that of all her concerns during pregnancy, air pollution was not one of them.
"It's very scary," she said, "you protect yourself when you find out you're pregnant in every way possible and that this is going to be something that people can not protect themselves so easily, living in London especially, it's pretty scary."