Index of air quality in the world's major cities: April 20

City

Average 19/04/2012

Average 20/04/2012

London

Madrid

Paris

Brussels

Berlin

Prague

Zurich

Beijing

Beijing

US embassy stats

Shanghai

Hong Kong

Brunei

Seoul

New York

San Francisco

Mexico City

Montreal

Toronto

New Delhi

Sydney

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.

Data for Beijing is taken from an average reading given across six districts by the Beijing Municipal Environmental Monitoring Center.

All data was collected at 9:30 am GMT on April 20.