1. What is an Air Pollution Index (API)?

An API comes from transforming many complicated air quality data measured at an air quality monitoring station into a single number ranging from 0 to 500, for the easy understanding of the public. Depending on the type of air quality monitoring station it relates, an API can either be a General API or a Roadside API.

The range of an API is divided into five bands: Low (0 to 25), Medium (26 to 50), High (51 to 100), Very High (101 to 200) and Severe (201 to 500).

2. What purpose does the API and Forecast System serves?

The API and Forecast System serves to give timely air quality information to the public in a simple manner, to advise people before the onset of high air pollution levels, and to enhance the awareness of the community on air pollution.

3. How is an API calculated and forecasted?

An API is calculated from comparing concentrations of five air pollutants (nitrogen dioxide, sulphur dioxide, ozone, carbon monoxide, respirable suspended particulates) against air pollution levels with reference to the Hong Kong Air Quality Objectives (AQO). Four specific API numbers are set to correspond to the different AQO levels as follows:

The Environmental Protection Department calculates and releases the APIs every hour, and at 4 p.m. everyday makes a forecast on the range of API numbers expected for the next 24 hours.

Please click here for an explanation on the AQOs.

4. Where can I get the latest APIs and the forecast?

You can find the latest APIs every hour and the forecast by visiting the Environmental Protection Department web site at http://www.epd.gov.hk/epd/ and clicking 'Air Pollution Index'. If you do not have an access to the Internet, you can alternatively call the API hotline on 2827 8541 for either a verbal advice, or a fax copy of the information on demand. The service is available 24 hours a day, 365 days a year.

You may also watch or listen to the API reports on the TV or radio.

5. What does the API mean to me?

You get the most updated API so that you can decide whether you want to engage in or to take special precautions before you engage in rigorous outdoor activities particularly if you are sensitive to air pollution.

6. Does the API reflect the air pollution level for a particular hour or a longer period?

The API of each monitoring station is determined every hour from the air pollution levels measured in the past 24 hours or in the past hour, whichever is the higher. The 24-hour and the one-hour period are of concern because air pollution health effects for different air pollutants are observable over exposures to either one or both of these periods.

7. What are the health implications associated with the different API bands?

A broad guide to the health implications corresponding to the different API bands is as follows:

8. What is the General API and the Roadside API?

The General API reflects the level of air pollution which you are exposed to most of the time. It comes from measurements at 11 general air quality monitoring stations of the Environmental Protection Department.

On the other hand, the Roadside API tells you the level of air pollution at the roadside with very heavy traffic and tall surrounding buildings. There are altogether three roadside air quality monitoring stations.

9. Where are the General and the Roadside API stations?

The locations of the 11 general air quality monitoring stations and the characteristics of the area each station represents are as follows:

The locations of the three roadside air quality monitoring stations and the type of roadside conditions each station represents are as follows:

10. Which one of the APIs is more relevant to me - General or Roadside?

If you spend most of your time away from roadside, the General API is more relevant. The adverse health effects of air pollution usually come about after longer than just a brief exposure to moderately high pollution levels at roadside.

The Roadside API is more relevant to people spending most of their time daily at roadside which is very heavy in traffic and surrounded by tall buildings.

11. Which General APIs should I refer to if no API is reported for the district I am living in?

You may refer to the APIs of those stations with development characteristics closest to the area you live in.

12. Is the API an average of the pollution levels measured at a monitoring station?

It is not an average. It is the highest API number calculated from the concentrations of the different air pollutants recorded at the monitoring station in the past one-hour or 24-hour whichever is the higher.

13. Are there any other countries using the same or a similar API system?

Yes. API systems are similar throughout the world, such as in the USA, Canada, Australia, Taiwan, Singapore, the Philippines, Korea, Mexico and Finland. Some cities report API more frequent than daily. For example, Singapore reports API every three hours, and Melbourne and Taipei report API every hour.

14. What should I do if the hourly API or its forecast is higher than 100?

Don't panic. When the API is between 101 and 200, the health effects are mild and mainly those people who are susceptible to air pollution (e.g. those with breathing or heart problems) may be affected. If you are one of them, you should reduce physical exertion and outdoor activities (especially in areas with poor air quality such as at busy roadside). When the API is between 201 and 500, a normal person may feel uncomfortable and you should reduce physical exertion and outdoor activities. If you are a cigarette smoker, you should stop smoking. Please seek advice from a medical doctor if you feel uncomfortable.

15. What precautionary measures should I take if the Roadside API is greater than 100?

If the Roadside API exceeds 100, people who are the most likely to be affected are those with existing heart and respiratory diseases. If you are one of them, you should avoid staying in busy streets with heavy traffic for extended periods. If the Roadside API is above 200, all of the population should avoid staying for extended periods in busy streets with heavy traffic.

16. Do I need to do anything when the API is between 51 and 100 in the "high" band?

The 'high' band serves as a reminder that air pollution with an API between 51 and 100 is not satisfactory and may cause long-term health effects if people are exposed to it persistently. As the air pollution at this level would not lead to significant immediate health effects, precautionary response action is not necessary.

17. The visibility can be quite poor on days with API higher than 100. Is visibility a better indicator of our air pollution than the API?

Visibility is not a good indicator of air pollution. Although air pollution affects visibility, there are other factors such as relative humidity, fog, mist and precipitation contributing to poor visibility.

18. Are air cleaning devices useful to reduce the air pollution at home during unhealthy air pollution incidents?

Properly designed and operated air cleaners may help to reduce the level of fine particles. If you decide to use an air cleaning device, you may like to read the Consumers Council's article published in their magazine "Choice" of 15 May 1997 on the performance of air cleaners.

19. Is wearing masks useful when the API is higher than 100?

Some special masks known as "respirators", designed for the protection of workers exposed to occupational health hazards, have good collecting efficiency in filtering respirable suspended particulates (but not gaseous air pollutants such as nitrogen dioxide and ozone). However, as they are uncomfortable and increase the effort of breathing, you may need to seek the advice of your doctor as to whether you are able to wear these respirators.

Given that our API seldom exceeds a level that warrants the adoption of protective measures, we do not consider it necessary and effective for a normal person to wear masks.

20. What can I do if I still have other queries or require further information on API?

Please feel free to contact us by writing to the following address or giving us a call or a fax.

Air Science Group,

Environmental Protection Department,

33/F., Revenue Tower, 5 Gloucester Road,

Wan Chai, Hong Kong.

Telephone: 28278541, 25946413

Fax: 28278040