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Information - Air Pollution Index (API)
The Air Pollution Index measures the amount of the 4 main greenhouses gases (sulphur dioxide, carbon monoxide, ozone and nitrogen dioxide) in a day based on the possible health effects of air pollutants. API is measured at Particulate Matter (PM) 10 or less.
Two API's are measured in Hong Kong: General API and Roadside API. Hong Kong is the first city in the World to issue a Roadside Air Pollution Index on a regular basis. Hong Kong has used the API since it was first introduced in 1995.
Below is the advice given out to the public in relation to the API level. Also compared are the Singapore/Taiwan Pollutant Standard Index (PSI) and the USA/Canada Air Quality Index (AQI).
| Hong Kong Air Pollution Level | Hong Kong Air Pollution Index (API) | Advice to Public | |||
|---|---|---|---|---|---|
| Hong Kong General API | Hong Kong Roadside API | Singapore/Taiwan Pollutant Standard Index (PSI) | USA/Canada Air Quality Index (AQI) | ||
| Severe | 201-500 | The general public are advised to reduce physical exertion and outdoor activities | The general public are advised to avoid prolonged stay in areas with heavy traffic. If it is necessary to stay in streets or roads with heavy traffic, they are advised to reduce physical exertion as far as possible. | PSI 201-300 PSI 301-400 Hazardous PSI 401-500 |
AQI 201-300 AQI 301-500
|
| Very High | 101-200 | Persons with existing heart or respiratory illnesses are advised to reduce physical exertion and outdoor activities | Persons with existing heart or respiratory illnesses are advised to avoid prolonged stay in areas with heavy traffic. If it is necessary to stay in streets or roads with heavy traffic, they are advised to reduce physical exertion as far as possible. | PSI 101-200 Unhealthy Mild aggravation of symptoms among susceptible persons. Those with underlying conditions such as chronic heart or lung ailments; transient symptoms of irritation. Eye irritation, sneezing or coughing in some of the healthy population |
AQI 101-150 AQI 151-200 |
| High | 51-100 | No immediate response action is suggested Long-term effects may, however, be observed if exposed at this level persistently for months or years |
PSI 51-100 Moderate Few or none for the general population |
AQI 51-100 Moderate Largely acceptable, poses risk to a minority. |
|
| Medium | 26-50 | No response action is required. | PSI 0-50 Good None |
AQI 0-50 Good Acceptable air quality; minimal risks |
|
| Low | 0-25 | No response action is required. | |||
Particlulate Matter (PM)
The term "particulate matter" (PM) includes both solid particles and liquid droplets found in air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as "fine" particles. Sources of fine particles include all types of combustion (motor vehicles, power plants, wood burning, etc.) and some industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse." Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.
Both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Adverse health effects have been associated with exposures to PM over both short periods (such as a day) and longer periods (a year or more).
- When exposed to PM, people with existing heart or lung diseases such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease are at increased risk of premature death or admission to hospitals or emergency rooms.
- The elderly also are sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases.
- When exposed to PM, children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath.
- PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.
Pollutant Standard Index (PSI)
PSI measures the concentrations of pollutants in the air, in parts per million. It measures particulate matter smaller than 10 (PM10) and is used mainly for media broadcasting. The PSI was developed by the United States Environmental Protection Agency (USEPA). In 1999, US EPA changed the PSI to the AQI so that it will be more accurate in calculating PM2.5 and ozone gases rather than just PM10.
Air Quality Index (AQI)
AQI measures mainly the ground-level ozone and volatile organic compounds (VOCs) in the presence of sunlight, which is brought about by mainly human activities. Particulates (fine particles of either solid or liquid suspended in the air) may also include sulphur dioxide and nitrogen dioxide, a gas poisonous to inhale, but is still a common air pollutant. It is more sensitive than PSI, measuring particulate matter smaller than 2.5 (PM2.5).
Depending on the PM level, different precautionary measures are required. PM2.5 typically lists more precautionary measures than PM10, due to the smaller size of the particles. For example, for an AQI of 101-150 (unhealthy for sensitive groups) and PM2.5, people with heart disease, the elderly and children are also recommended to limit prolonged exertion. PM10 for the same API states that only people with respiratory disease, such as asthma, should limit outdoor exertion.