Deaths related to air pollution exposure in Yorkshire's towns and cities are now 21 times more likely than road deaths, data analysts estimate.
Toxic particles in the air are responsible for the deaths of more than one in 24 people in the region exposed to them over time, says a study by research institute Centre for Cities.
These deaths are connected to long-term exposure to deadly yet "entirely legal" PM2.5 particles, which are present in emissions from petrol and diesel vehicles, as well as burning fossil fuels and seemingly-harmless wood burning stoves.
One Yorkshire scientist described long-term exposure to such particles as equivalent to "slowly poisoning your body", with some smaller particles emitted from car exhausts tiny enough to penetrate human cell walls and enter the bloodstream.
A total of 1,514 people in Yorkshire each year are killed by conditions connected to the long term exposure to PM2.5, such as lung cancer and asthma, according to the most recent data available in 2017.
More worryingly, there is no law regulating levels of PM2.5 in England, Wales and Northern Ireland, despite guidelines set by the World Health Organisation (WHO).
Centre for Cities has named Hull, Leeds and Bradford as the region's worst locations for deaths connected to air quality.
Exposure to PM2.5 is thought to be responsible for 4.9 per cent of all adult deaths annually (128) in Hull, 4.5 per cent of deaths in Leeds (300) and 4.3 per cent in Bradford (191).
Other towns and cities named in the report were Doncaster (4.3 per cent of deaths) and York (4.3 per cent).
Authorities in Bradford have said they "absolutely recognise" that emissions are "costing lives", while Leeds City Council has stressed it is introducing a Clean Air Charge Zone later this summer.
Data analyst Kathrin Ennenken, who produced the report, said the real death toll was likely "much higher" than the figures suggest, due to it not accounting for other pollutants such as nitrogen dioxide.
Speaking to The Yorkshire Post, she said: "People are dying because of PM2.5.
"It is the most deadly pollutant because it is such a small particle and is the most easily trapped in the human respiratory system.
"The long term exposure to PM2.5 causes conditions like lung cancer, it stems the growth of children's lungs and increases the risk of strokes and cardiac arrest."
Dr Jim McQuaid, Associate Professor of Atmospheric Composition at Leeds University, researches air quality.
He said: "There are two main forms of air pollution - that is, nitrogen dioxide, which is a gas produced from combustion in vehicles, and particulate matter, which is dust and particles in the air . Braking vehicles produce it, as well as candles and air fresheners. Wood burning stoves are also a huge source of PM2.5.
"It can also be blown in the wind over from Europe."
Dr McQuaid added: "We also measure ultra fine PM1 particles, which are produced from cars and are so small they pass through cell walls and get into the blood stream.
"Overall, it's very difficult to quantify, but everything suggests that a child growing up exposed to air pollution is not going to live as long a life.
"It can make people more susceptible to other illnesses; it also can affect unborn children.
"You're basically feeding poison very slowly into your body over time."
Coun Sarah Ferriby, from Bradford Metropolitan District Council, said: "We absolutely recognise the seriousness of poor air quality. Quite literally it costs lives.
"Improving the air quality is therefore a major priority for the Council. This is why we are working closely with the government to put in place a wide range of interventions to reduce pollution in the shortest possible time."
Authorities across Yorkshire are taking urgent measures to reduce air pollution, with Leeds City Council responding to the report saying it is spending £23m to help people switch to electric vehicles and raising awareness of engine 'idling'.
Coun James Lewis, Leeds council member responsible for air quality, said: “Everyone that lives or works in Leeds shares a responsibility for cleaning the air we share and there are lots of ways to help. Individuals can do their bit by using the car less often, sharing their journeys more often, and by turning off their engines when idling.”
The Yorkshire Post also reached out to Hull City Council for comment, although it failed to respond.
However, experts say this is still not enough, and that the government needs to be urgent in addressing the issue.
Andrew Carter, Chief Executive of Centre for Cities, said: "People in Yorkshire should be at the centre of the fight against its toxic air and councils should take the steps needed, including charging people to drive in city centres and banning wood-burning stoves.
"To help, the government needs to provide Yorkshire's councils with extra money and introduce stricter guidelines. The deadly levels of polluted air in Yorkshire are entirely legal. This needs to change. As a matter of urgency, the government should adopt WHO's stricter guidelines around PM2.5 emissions.
"Failure to act now will lead to more deaths in Yorkshire."