Two million people a year killed by air pollution

According to new research examined by the World Health Organization (WHO), air pollution in cities around the world causes roughly 2 million premature deaths each year.

The WHO warned that in order for some cities to meet its recommendations, levels of pollution would need to be cut by as much as three fold. Because many countries currently lack any air pollution standards and many countries are still developing, the WHO acknowledged its guidelines could be difficult to follow.

The organization's recommendations include reducing levels of particulate matter -- known as PM10 and produced mainly by the burning of fossil fuels -- to 10 to 20 micrograms per cubic meter. Many cities currently have PM10 levels in excess of 70 micrograms per cubic meter. PM10 has been linked to respiratory illness and heart disease, and the WHO says reducing these harmful particulate matter levels can reduce deaths from air pollution by 15 percent per year.

The daily limit for ozone -- a key component of smog -- will be reduced from 120 micrograms per cubic meter to 100 micrograms. The WHO notes that this reduction could be problematic for many cities, especially those with a high number of sunny days, when ozone concentrations are high and cause asthma attacks and other respiratory problems.

Finally, the organization recommends cutting levels of sulfur dioxide from 125 micrograms per cubic meter to 20 micrograms. Cutting this pollutant would result in fewer childhood diseases and deaths, the researchers say.