Index of air quality in the world's major cities: January 19

(AFP PHOTO / NASA EARTH OBSERVATORY)

Daily air quality index of some of the world's major cities on January 19, using data from AirNow, CITEAIR, and the American Embassy in Beijing.

City	Average 18/01/2011	Average 19/01/2011
London (UK)	Good	Good
Madrid (Spain)	Moderate	NA
Paris (France)	Good	Good
Brussels (Belgium)	Good	Good
Berlin (Germany )	Good	Good
Prague (Czech Republic)	Good	NA
Zurich (Switzerland)	Good	Good
Beijing (China)	Good	Good
Beijing - US embassy stats	Moderate	Good
Shanghai (China)	Good	Good
Hong Kong (China)	Good	Moderate
Brunei (Brunei)	Good	Good
Seoul (South Korea)	NA	Moderate
New York (USA)	Moderate	Moderate
San Francisco (USA)	Moderate	Moderate
Mexico City (Mexico )	Moderate	Unhealthy for sensitive groups
Montreal (Canada)	Good	Moderate
Toronto (Canada)	Good	Good
New Delhi (India)	Unhealthy	Unhealthy
Sydney (Australia)	Good	Good

The Air Quality Index (AQI) or Air Pollution Index (API) measures the parts of pollutant in a specified volume of air. The lower the AQI the fewer particles of pollution are in the air. For a more detailed explanation see http://www.airnow.gov/index.cfm?action=aqibasics.aqi.

All results are color-coded following the American AQI standard shown below. For all countries outside of Europe, the US and Canada, that region's definition of AQI terms has been accepted.

Legend 

Air Quality
Good
Moderate
Unhealthy for sensitive groups
Unhealthy
Very Unhealthy
Hazardous

Data: Data relating to Europe, the US and Canada is taken from CITEAIR - Common Information to European Air ( http://www.airnow.gov / http://www.airqualitynow.eu); data concerning China is taken from both official Chinese government sources and the US Embassy's automated air index Twitter account. For all countries the data displayed falls within either that country's definition of the level of air quality or the international AQI index. Data for all European, US and Canadian cities refers to background, not roadside, levels of air quality.

All data was collected at 9:00am GMT on January 19.

http://www.airqualitynow.eu
http://www.airnow.gov