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API and Air Monitoring Background Information
Air Pollution Index Background Information
API Calculation
Method API is the conversion
of the ambient respirable suspended particulate (RSP), sulphur dioxide
(SO2), carbon monoxide (CO), ozone (O3) and
nitrogen dioxide (NO2) concentrations measured at our
air quality monitoring network to a
scale of 0 to 500. An index of 100 corresponds to the short-term
Hong Kong Air Quality Objectives (HKAQO) estabished
under the Air Pollution Control Ordinance. Real time air
quality data from each monitoring station are transferred via telephone
line to the air quality data processing centre of EPD in Revenue
Tower for calculation of API. API is calculated by first computing
the subindices of scale extending from 0 to 500 for each air pollutant
measured at each air quality monitoring station based on the 1-hour,
8-hour and/or 24-hour average concentrations. Subindex
levels have been related to ambient pollutant concentrations
over a 24 hour period based on the potential health effects of pollutants.
A subindex level of 100 corresponds to the short-term Hong Kong
Air Quality Objectives (HKAQO) below which there is no adverse acute
health effect to human while a level of 500 corresponds to significant
harm to human health. API is subsequently calculated for each air
quality monitoring station by taking the maximum of the subindices
among all the parameters measured at that station to indicate the
overall pollution level.
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