Air Quality Objectives

Hong Kong’s Air Quality Objectives

The Government has set out Hong Kong’s Air Quality Objectives (AQOs) in the Air Pollution Control Ordinance (Cap. 311), and is required to review the AQOs at least once every five years and submit a report of the review to the Advisory Council on the Environment. 

Hong Kong Air Quality Objectives

Pollutant Averaging time Concentration limit [i]  (μg/m3) Number of exceedances allowed

Sulphur dioxide

10-minute

500

3

24-hour

40

3

Respirable suspended particulates (PM10) [ii]

24-hour

75

9

Annual

30

Not applicable

Fine suspended

particulates (PM2.5) [iii]

24-hour

37.5

18

Annual

15

Not applicable

Nitrogen dioxide

1-hour

200

18

24-hour

120

9

Annual

40

Not applicable

Ozone

8-hour

160

9

Peak season

100

Not applicable

Carbon monoxide

1-hour

30,000

0

8-hour

10,000

0

24-hour

4,000

0

Lead

Annual

0.5

Not applicable

 

Note:

 

[i]
All measurements of the concentration of gaseous air pollutants, i.e., sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide, are to be adjusted to a reference temperature of 293 Kelvin and a reference pressure of 101.325 kilopascal.
[ii]
Respirable suspended particulates (PM10) means suspended particles in air with a nominal aerodynamic diameter of 10 μm or less.
[iii]
Fine suspended particulates (PM2.5) means suspended particles in air with a nominal aerodynamic diameter of 2.5 μm or less.

Air Quality Management in Hong Kong

The overall policy objective for air quality management in Hong Kong is to achieve as soon as reasonably practicable and to maintain thereafter an acceptable level of air quality to safeguard the health and well-being of the community, and to promote the conservation and best use of air in the public interest. In this regard, we put in force an updated Hong Kong's AQOs on 11 April 2025 to further protect public health.

The prevailing AQOs are benchmarked against a combination of interim and ultimate targets under World Health Organisation's (WHO) WHO Global Air Quality Guidelines (AQGs). To continuously improve air quality, we have implemented a wide range of measures to control emissions from power plants, industrial and commercial activities, motor vehicles and marine vessels, as well as setting regional emission reduction targets for key air pollutants together with the Guangdong Provincial Government. The overall air quality of Hong Kong has been improving in recent years, with concentrations of major air pollutants continuously decreasing and remaining at low levels since Hong Kong’s return to the motherland.

The Government will review the AQOs at least once every five years to monitor the progress of air quality improvement and the effectiveness of measures. The Government’s ultimate goal, in the long run, is for Hong Kong’s air quality to fully meet the ultimate targets set out by the WHO.

Download the Table of AQOs

Historical Air Quality Objectives and Reviews

Air Pollution Control Strategies

 

Related Documents

WHO global air quality guidelines. particulate matter: (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide: executive summary (2021)

WHO global air quality guidelines. particulate matter: (PM2.5  and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide (2021)

WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulphur Dioxide, Global Update 2005

 

Links

Air Quality of Hong Kong

Air Quality Health Index

Air Quality Reports

Mainland China and Overseas Air Quality Objectives/Standards

The Mainland of China

Australia

Canada

EU

Japan

Korea

Singapore

USA

UK

 

 

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