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 to humans.
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 is 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.