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Health Effects
API levels have been related to concentrations of ambient respirable suspended particulate (RSP), sulphur dioxide (SO2), carbon monoxide (CO), ozone (O3) and nitrogen dioxide (NO2) over a 24-hour period based on the potential health effects of air pollutants.
API level at or below 100 means that any pollutant levels are in the satisfactory range over 24 hour period, which poses no acute or immediate health effects. However, air pollution consistently at 'High' levels (API of 51 to 100) in a year may mean that the annual HKAQO for protecting long-term health effects could be violated. Therefore, chronic health effects may be observed if one is persistently exposed to API of 51 to 100 persistently for a long time.
An API level in excess of 100 means that levels of one or more pollutant(s) is/are in the unhealthy range. The EPD has provided advice to public regarding precautionary actions to take for such levels.
| API |
Air Pollution
Level |
Health Implications |
| 0 to 25 |
Low |
Not expected |
| 26 to 50 |
Medium |
Not expected for the general population |
| 51 to 100 |
High |
Acute health effects are not expected but chronic effects may be observed if you are exposed to such levels persistently for a long time. |
| 101 to 200 |
Very High |
People with existing heart or respiratory illnesses may notice mild aggravation of their health conditions. Generally healthy individuals may also notice some discomfort. |
| 201 to 500 |
Severe |
People with existing heart or respiratory illnesses may experience significant aggravation of their symptoms. There will be also widespread symptoms in the healthy population (e.g. eye irritation, wheezing, coughing, phlegm and sore throats). |
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