Air pollution 'an invisible killer'

Outdoor air pollution is estimated to contribute to more than two-and-a-half million deaths each year, a study has suggested.
It calculated that, each year, 470,000 people died as a result of ozone and 2.1 million deaths were linked to fine particulate matter.
Air pollution increased respiratory and heart disease risks, with the young, elderly and infirm most vulnerable.
The findings appear in the Environmental Research Letters journal.
"Epidemiological studies have shown that ozone and PM2.5 (particulates with a diameter of less than 2.5 microns - about 30 times thinner than the width of a human hair) have significant influences on human health, including premature mortality," an international team of scientists wrote.
In order to reach their estimate, the researchers compared the results from a range of earlier mathematical models on deaths from air pollution.
They found that their total was lower than previous estimates.
But the team added: "Our methods likely underestimate the true burden of outdoor pollution because we have limited the evaluation to adults aged 30 and older.
"On the other hand, recent studies suggest that the relationship between PM2.5 and mortality may flatten at high concentrations, suggesting that we may overestimate PM2.5 mortality in regions with very high concentrations."
Global problem
The World Health Organization (WHO) says it is difficult to identify the world's most
polluted areas because many cities with high levels of air pollution do not have monitoring systems in place.
"Nevertheless, the available data indicates that air pollution is very high in a number of Asian cities (Karachi, New Delhi, Kathmandu, Beijing), in Latin American cities (Lima, Arequipa) and in Africa (Cairo)," it observes.
But the WHO adds that although most air pollution hotspots are located in developing nations, it says that developed countries are also at risk and the issue is a major environmental risk globally.
As air quality is largely beyond the control of an individual, the WHO says action needs to be taken by national and international bodies.