Author: John Lee, Antonio Da Roza

Originally: Department of Community Medicine, HKU

Date: 8/8/10

Originally 27 November 2006

How does air pollution affect health?

- Causes damage to body tissues – especially eyes, nasal passages, lungs, blood vessels and the heart.

- Causes severe illness episodes and shortens life expectancy. Longer term effects include cardiopulmonary problems and increase the risk of lung cancer.

- Impairs normal development of lung function in young people – a lifetime defect by the time they reach 18 years old.

- Most of the current evidence in HK is based only on short term effects which are likely to underestimate the total health impact of air pollution on the population.

- Pollutants enter the blood circulation of pregnant mothers and damage unborn infants.

- Also increases susceptibility to infection, development of atherosclerosis in blood vessels, and interfe res with the normal neuro-electrical control of the heart.

- Complex chemicals common in pollutant mixtures damage body tissues through oxidative stress, because of the presence of several highly reactive free radicals. Oxidative stress is a series of reactions which may be caused by smoking, alcohol abuse, radiation, exposure to cold and air pollution.

- Free radicals produce an inflammatory response in lungs first and later throughout the body. Our lungs have a surface area approximately the size of a tennis course and they are the first target of inhaled environmental pollutants.

Which pollutants are harmful to health?

“Criteria pollutants” are used to estimate health effects: respirable suspended particulates (RSP or PM10), nitrogen dioxide (NO2), sulphur dioxide (SO2) and ozone (O3). All four pollutants show significant associations with adverse health effects.

However, for adverse health outcomes in terms of hospital admissions and death risk, estimates are consistently higher for nitrogen dioxide and sulphur dioxide than for particulates.

Most of the estimated bad health outcomes are occurring at levels of pollution which are well below the present Hong Kong Air Quality Objectives.

Who is most affected?

The greatest health risks air pollution presents are to young children and older people from middle age (eg. 45 years old) onwards, as well as those who have other health risks (i.e. active or passive smoking, poor nutrition, heart or lung disease).

The current situation

Unfortunately, at present any proportional reductions in concentrations are small in relation to the high average levels of are pollution. Uncertainties in the data (omissions of monitoring data) and yearly fluctuations in pollutants are not properly taken into account, which could lead to flawed policies if formed on the basis of that data. Trends in emissions from power generation, marine and civil aviation sources (58% of the total) all reflect increases. Extrapolating from these current trends in pollutant levels indicate that there will be no reasonable health protection from air pollution in Hong Kong in the foreseeable future.

Community costs of air pollution

The difference between Hong Kong’s average pollution levels and much lower levels which are close to the new WHO Guidelines is estimated to be the cause of a large scale epidemic of disease. Losses include 6.8 million doctor visits for respiratory complaints alone, over 60,000 hospital bed days and about 1600 deaths, which translate into annual direct (health care) and indirect (lost productivity) costs of about $2 billion and a further $19 billion for the intangible costs.

AQOs and Air Pollution Index

The current Air Pollution Index (API) is derived from the AQOs. Our lax AQOs lead to lower API values, which are in turn misleading for the public as they under-represent the health impacts of the ambient air. Hence, with or without the revision of AQOs, the API should immediately be revised according to the WHO AQGs.

AQOs and Environmental Impact Assessment (EIA)

While EIA approval is currently anchored with the AQOs, the use of verifiable emission offsets could be considered for new projects (similar to the emissions trading scheme). Further, initially, the EIA approval can be modified to anchor with a set of WHO Interim Targets, rather than the WHO AQGs.

The ultimate benchmark must be the WHO AQGs, and if we adopt the Interim Target(s), we must also have a clear time-table for the EIA anchors to converge to the WHO AQGs.

Long-term Air Quality Management Strategy

Tightening our AQOs is just the first step. We need a comprehensive study to map out a long-term air quality management strategy. While highlighting the substantial cost for improving air quality, the study must also look at and document clearly the tangible and intangible impacts for Hong Kong (and the Pearl River Delta) if we fail to act.

Any action plans to be developed must have a clear time-frame, and be associated with health-based milestones. These health-based milestones must ultimately converge to the WHO AQGs. We must be prepared to go beyond simple control measures for emissions reductions to include planning measures, new policies and life-style changes if we are to achieve better air quality.


  1. - last accessed 8/8/10

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