A billboard blocks the view of a construction site against the backdrop of a polluted skyline in Beijing, May 2. A billboard blocks the view of a construction site against the backdrop of a polluted skyline in Beijing, May 2. (Oded Balilty/Associated Press)

Organizers of the Beijing Summer Games have another, unofficial Olympic motto as they try to combat air pollution in the days before the opening ceremony: cleaner, fresher, healthier.

It's a massive job for the city, cited as the world's 13th-most polluted in one measure of air pollution. Cars have been taken off the roads, factories shut and construction projects halted, all in the name of clearing the air.

How does Beijing compare?

Rankings of selected world cities based on annual readings of particulate matter (PM10), tiny airborne particles that enter the atmosphere through car emissions, burning of fossil fuels and other methods.

City PM10 level (2004)
Cairo 169
Delhi 150
Jakarta, Indonesia 104
Beijing 89
Mexico City 51
Rio de Janeiro 35
Los Angeles 34
Toronto 22
New York 21
Montreal 19
Vancouver 13
Other recent Olympic cities
Athens 43
Seoul 41
Sydney 20

Source: World Bank 2004 (PDF)

A great deal of progress has been reported. Beijing's air quality monitoring program noted a drop in pollution levels in recent months. There were 12 more "blue sky" days (where the air quality is fair or better) in the first half of the year than in the same period in 2007, according to the state-run Xinhua news agency.

A 2006 report from a United Nations environmental agency found levels of many pollutants, such as carbon monoxide, had dropped consistently in previous years. It praised China's efforts to clear the air and noted that levels of many pollutants dipped in the summer months — good news for officials promising an easy-breathing event.

But the report, which relied heavily on Chinese government statistics, noted that there were "legitimate concerns" about pollution in Beijing.

And less than two weeks before the opening ceremonies, hazy, grey conditions were reported over the city.

That blue skies are proving difficult to maintain should not be a surprise given the severity of the problem Olympic organizers have been trying to overcome.

An economic boom fueled by coal-powered industries and citizens' deepening love affair with automobiles are often blamed for Beijing's air woes. Geography also does the city no favours.

"The mountain ranges that surround Beijing block air circulation and prevent the dispersion of pollutants," said the 2006 UN report.

When winds do blow away the smog, the city risks being inundated with pollutants blowing in from factories in China's other industrial cities. In the spring, dust storms can blanket the city with sand blown in from encroaching deserts about 250 kilometres away.

A World Bank survey released in 2007 found that annual measurements in Beijing for three elements that contribute to the toxic soup known as smog — airborne particulate matter, sulphur dioxide and nitrogen dioxide — were well above guidelines set by the World Health Organization.

Noting that pollution levels vary widely by the day and location of measurement, the World Bank report used numbers from 1995 to 2004 to come up with a snapshot of air quality in the world's cities.

Map: Air pollutant levels in selected world cities

Click on a red dot above to see the city's pollution levels. Source: World Bank, 2007 World Development Indicators

Definitions

Particulate matter refers to fine, suspended particulates less than 10 microns in diameter (PM10) that are capable of penetrating deep into the respiratory tract and causing significant health damage.

Sulfur dioxide is an air pollutant produced when fossil fuels containing sulfur are burned. It contributes to acid rain and can damage human health, particularly that of the young and the elderly.

Nitrogen dioxide is a poisonous, pungent gas formed when nitric oxide combines with hydrocarbons and sunlight, producing a photochemical reaction. It is emitted by bacteria, motor vehicles, industrial activities, nitrogenous fertilizers, combustion of fuels and biomass, and aerobic decomposition of organic matter in soils and oceans.

Source: World Bank