Outdoor air pollution is a leading cause of cancer in humans, according to the International Agency for Research on Cancer (IARC), an arm of the World Health Organisation (WHO).
The IARC said on Thursday that a panel of top experts had found "sufficient evidence" that exposure to outdoor air pollution caused lung cancer and raised the risk of bladder cancer.
The predominant sources of outdoor air pollution were transport, power generation, emissions from factories and farms, and residential heating and cooking, the UN agency said.
The most recent data, from 2010, showed that 223,000 lung cancer deaths worldwide were the result of air pollution, the report said.
"Our task was to evaluate the air everyone breathes rather than focus on specific air pollutants," said the IARC's Dana Loomis.
"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," he added.
Although the composition of air pollution and levels of exposure can vary dramatically between locations, the agency said its conclusions applied to all regions of the globe.
It said pollution exposure levels increased significantly in some parts of the world in recent years, notably in rapidly industrialising nations with large populations.
The latest findings were based on overall air quality, and based on an in-depth study of thousands of medical research projects conducted around the world over decades.
Air pollution was already known to increase the risk of respiratory and heart diseases.
"Classifying outdoor air pollution as carcinogenic to humans is an important step," said the IARC's director Christopher Wild.
"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 data did not enable experts to establish whether particular groups of people were more or less vulnerable to cancer from pollution, but Kurt Straif of IARC said it was clear that risk rose in line with exposure.
Diesel exhaust and what is known as "particulate matter" - which includes soot - have been classified as carcinogenic by the IARC.
The IARC said that it was set to publish its in-depth conclusions on October 24 on the specialised website The Lancet Oncology.