Video report by ITV Wales Correspondent Richard Morgan
Nearly two dozen homes are being razed on Wales' most polluted street as demolition work began today.
Proposals to demolish 23 homes on the A472 Hafodyrynys Road in Crumlin, Caerphilly county, started four years ago amid concerns over "dangerous" levels of air pollution.
In 2015 and 2016, nitrogen dioxide levels in the area were recorded as the highest in the UK outside of central London.
In 2018, it was revealed there were 69 units of nitrogen dioxide in the air. The legal amount is 40 units.
The issue is believed to be the shape of the valley, combined with the proximity of the houses to the busy road, creating a 'canyon' effect where the air cannot disperse.
Last year, more than £6m was granted to go towards demolishing the houses.
At the time, the Welsh Government said: "It is of the utmost importance we take action to reduce nitrogen dioxide levels to below legal limits in the soonest time possible to protect public health and the natural environment."
Caerphilly Council worked with the residents, offering 150% of the market value to ensure they weren't at a financial detriment.
Today the leader of Caerphilly Council, Phillipa Marsden, said the demolition work is "significant".
"This is going to be the quickest way that we can bring the levels down to a safer level for the residents here - so for me, it's absolutely vital that we start this work today," she added.
The work will take approximately 14 weeks to complete, including realignment of the footpath and road edge to widen the area so that air can disperse more readily.
Martin Brown bought a house on the polluted street with his wife more than 50 years ago.
He said he's both "relieved and upset" to be moving, but he and his wife both knew they had to because the pollution and traffic was "unbearable in the end".
Mr Brown says he feels frustrated that the traffic is just as bad on the street and nothing has changed.
"I feel sorry for the people left there on the other side of the street," he said.
"We had some good times at the address, we brought up children there - but the last five to ten years at the house, things just got worse. All the residents gave up. We knew we had to go."
What is air pollution?
Air pollution poses a major threat to health and climate, according to the World Health Organisation.
Air pollution refers to substances that are present in the air, or have entered the air, that have harmful or toxic effects.
It can come from many sources, travel across distances and interact with other molecules to cause different effects.
How does air pollution affect our health?
We all breathe it, and it's hard to avoid. Once it enters the lungs it could worsen any pre-existing conditions such as asthma, heart disease and respiratory infections.
It progresses through the bloodstream and can cause problems within the rest of the body.
If exposed to high levels of air pollution issues for long periods of time, more long-term damage is likely to occur with research showing people living in close proximity to a major road are more likely to develop dementia and lung cancer.
Healthy Air Cymru says that air pollution contributes to almost 1,400 early deaths.
Joseph Carter, Chair of Healthy Air Cymru, is calling on the Welsh Government to clean up Wales' air and ensure everyone can live a healthy and active life.
He said: "It’s vital that clean air remains a top priority for the new Welsh Government, no matter what form it may take.
"With many major political parties already backing our calls, Senedd candidates from all parties must strike while the iron is hot.
"Every day that goes on, every year that goes on, more and more people are being affected by air pollution.
"More people are dying from air pollution, so this is a real immediate issue that the Welsh Government needs to be taking seriously.
"We hope the pressure is put on the government from all sides to act on this."
A Welsh Government spokesperson said: “The environment is at the heart of our decision-making and we are committed to tackling the sources of pollution and ensuring people’s right to clean air in Wales.
"We fully recognise the importance for setting out targets in legislation as soon as possible and we will follow an evidence-based process to inform this work.”