Year 1996 1997 1998 1999 2000 2001 2002 2003
% 2 1 6.30 15 7.92 11.23 11.23 14.52
Year 2004 2005 2006 2007 2008 2009 2010
% 23.84 13.15 13.70 19.50 25.20 29 38.90

Operational Definitions

The percentage of days in which air quality of Hong Kong, as expressed in terms of the Air Pollution Index, reaches a level of pollution of either “very high” or “severe”. Since June 1995, the Environmental Protection Department (EPD) has been reporting the API and making forecast for the following day. In Hong Kong, the API converts air pollution data from several types of pollutants into a value ranging from 0 to 500, which is divided into 5 bands (Low 0-25, Medium 26-50, High 51-100, Very High 101-200, Severe 201-500) according to the potential effects on health. Generally speaking, an API higher than 100 means that one or more pollutants may pose immediate health effects to some susceptible members of our community (for details, please go directly to The latest general and roadside APIs are reported hourly. These indices are calculated by comparing the measured concentrations of the major air pollutants with their respective health related Air Quality Objectives (AQOs) established under the Air Pollution Control Ordinance. These pollutants are nitrogen dioxide, sulphur, dioxide, ozone, carbon monoxide and respirable suspended particulates. APIs for each of these five pollutants are recorded and the highest API number is reported as the API of that hour.


All figures are collected from Environmental Protection Department since 1981.
Since the API was established in 1995, figures for years before 1995 are not available.

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