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Long-term Health Risk of Air Quality

The EPD has taken a health risk-based approach to assess the long-term air quality of Hong Kong that would better reflect the impact of air quality on members of the public. This approach makes reference to the methodology developed by a research team in Hong Kong. While the AQHI provides information about the risk of short-term exposure to air pollutants, the “long-term health risk of air quality” provides information about the risk of long-term exposure to air pollutants. The air quality of Hong Kong has significantly improved in recent years both in terms of air pollutants concentrations and their health risks.


Improvement trend of Long-term Health Risk of Air Quality(2004 - 2024)

Remark: The lines of WHO IT-1, IT-2, IT-3, IT-4 and AQG represents the health risk equivalent to the interim
and ultimate targets of World Health Organization Global Air Quality Guidelines 2021 version.


The Long-term Health Risk of Air Quality is calculated from the sum of the added health risks (%AR) attributable to the peak season concentration of ozone (O3) and the annual average concentrations of nitrogen dioxide (NO2) and particulate matters (PM10 or PM2.5, whichever poses a higher health risk).


The equations are as follows:

%AR = %AR(NO2) + %AR(O3) + %AR(PM) where %AR(PM) = %AR(PM10) or %AR(PM2.5), whichever is higher

%AR(NO2) = [exp(β(NO2) × C(NO2)) – 1] × 100%
%AR(O3) = [exp(β(O3) × C(O3)) – 1] × 100%
%AR(PM10) = [exp(β(PM10) × C(PM10)) – 1] × 100%
%AR(PM2.5) = [exp(β(PM2.5) × C(PM2.5)) – 1] × 100%

where %AR(NO2), %AR(O3), %AR(PM), %AR(PM10) and %AR(PM2.5) are the added health risk of NO2, O3, PM, PM10 and PM2.5 respectively;

C(NO2), C(PM10) and C(PM2.5) are annual average concentrations of the respective pollutants in microgram per cubic meter (µg/m3).

C(O3) is the peak season ozone (O3) concentration in microgram per cubic meter (µg/m3)*.

β(NO2), β(O3), β(PM10) and β(PM2.5) are long-term health risk factors (technically known as regression coefficients) of the respective pollutants.

β(NO2) = 0.0019802627; β(O3) = 0.0009950331; β(PM10) = 0.0039220713; β(PM2.5) = 0.0076961041

*Remark: The WHO Global Air Quality Guidelines of 2021 version defined peak season O3 concentration as “average of daily maximum 8-hour mean O3 concentration in the six consecutive months with the highest six-month running-average O3 concentration”.