FRESH air laced with pollution should now be classed as carcinogenic, the World Health Organisation's (WHO) cancer agency has said.
Outdoor air pollution is a leading environmental cause of cancer deaths, the International Agency for Research on Cancer (IARC) announced as it classified outdoor air pollution as carcinogenic.
It listed the main sources of outdoor air pollution as transport, power generation, industrial and agricultural emissions, and heating and cooking in residential buildings.
Some air pollutants also have natural sources, it added.
IARC director Dr Christopher Wild said in a statement: "Classifying outdoor air pollution as carcinogenic to humans is an important step.
"There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay."
The team said there was sufficient evidence that exposure to outdoor air pollution causes lung cancer. It is also linked to an increased risk of bladder cancer.
In 2010, 223,000 deaths from lung cancer worldwide resulted from air pollution, the IARC said.
Researchers said that although the composition of air pollution and levels of exposure can vary dramatically between areas, their findings apply to all regions of the world.
Air pollution is already known to increase risks for a wide range of diseases, such as respiratory and heart diseases.
Dr Kurt Straif, head of the IARC monographs section, said: "The air we breathe has become polluted with a mixture of cancer-causing substances.
"We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths."
Dr Dana Loomis, deputy head of the monographs section, said: "Our task was to evaluate the air everyone breathes rather than focus on specific air pollutants.
"The results from the reviewed studies point in the same direction: the risk of developing lung cancer is significantly increased in people exposed to air pollution."
Dr Julie Sharp, head of health information at Cancer Research UK, said: "Air pollution has been linked to a small increase in the risk of lung cancer for some time, so this isn't a surprising development.
"The evidence about air pollution and cancer is plentiful but of mixed quality, so the IARC's new assessment that overall there is strong evidence for a link is helpful to understanding this complex topic.
"It's important that people keep the risk from air pollution in perspective," she said.
"Although air pollution increases the risk of developing lung cancer by a small amount, other things have a much bigger effect on our risk, particularly smoking. The risk from air pollution depends on the levels of regular exposure.
"Cancer Research UK wants the Government and relevant authorities to introduce measures that reduce air pollution to levels within EU limits to protect people's health.
"And walkers and cyclists can also help themselves by avoiding busy roads when possible."
The IARC said in recent years that exposure levels have increased significantly in some parts of the world – particularly in rapidly industrialising countries with large populations.