Author: Candy Au, Antonio Da Roza

Originally: Department of Community Medicine, HKU; The Air Quality Objective Concern Group (published by Civic Exchange)

Date: 9/8/10

Originally: October 2007

Poor visibility is directly related to trends and episodes in air pollution. Loss of visibility is also a direct measure of illness and deaths caused by air pollution.

Timely and effective improvement in regional air quality needs to come from legislation and mandatory comprehensive interventions on emissions in all sectors, in a way which will reduce the pollutant concentrations of the air

A reduction of HK’s average annual pollutant levels down to the levels of WHO guidelines would avoid nearly 7 million doctor visits, over 60,000 hospital bed-days and up to 1,600 deaths each year. The attributable direct cost of health care and lost productivity is about $2 billion per annum. The intangible costs of pollution measured in terms of willingness-to-pay, to avoid a day of respiratory symptoms such as cough, a hospital admission for heart or lung problems and a premature death, all caused by breathing pollutants value around $20 billion each year. Damage to children’s lungs may be permanent and have lifelong effects on respiratory health and life expectancy. High Air Pollution alert days may prevent this.

Patterns of pollutant concentrations on very high pollution days show sharp divergent trends with the slope of the trend changing rapidly within an hour or two. The number of High Air Pollution alerts called will depend on the chosen criteria which could range from 1 day up to 359 days out of the year.

At present the High Air Pollution alert days would be signalled on the basis of an Air Pollution Index (API) calculated using the Hong Kong Air Quality Objectives (HKAQOs). The HKAQOs are now twenty years out of date as a scientific basis for health protection. It is scaled far too high with the effect that an API calculated on this basis will only trigger an alert when pollutants are well past harmful levels which cause both short and long term injury to heart and lungs.

It should be noted that the new WHO 24 hour guideline should not be exceeded on more than 3 days in a year. However applying this criterion in Hong Kong would result in alerts being called on 226 to 359 days a year.

The costs associated with mandatory measures during a High Air Pollution alert might be analogous to those incurred by a typhoon. An approaching storm is an uncertain business, leading to lost productivity and revenue, and may thus make it difficult for the community to accept another general warning system (they may view it as a source of reputational damage to Hong Kong).

The net gains to the community will be dependent on minimization of the impact on GDP and maximization of health protection.

Restrictions on private cars may not lead to significant reductions in regional pollutions because the major emission sources in HK are from marine and commercial vehicles and power generation – High Air Pollution alerts are not designed to reduce emissions from these sources. If High Air Pollution alerts keep more people indoors, power consumption may increase.

Moreover, staying at home is unlikely to confer any worthwhile health benefit for the majority of the public during a very high pollution episode. Those with the lowest and highest exercise levels have the highest pollution-related mortality risks after adjustment for other health risks. In the 1998 Hong Kong lifestyle and mortality study those who took no exercise had the highest mortality risks.

Any labelling schemes to identify employees at high health risk from air pollution are likely to be stigmatizing, may lead to prejudice and put the jobs of some at risk.

The principle cause of damage to children is caused by average daily high levels not simply the less common very high pollution days.


High Air Pollution alert days in Hong Kong would be a highly inefficient use of scarce resources. The estimated costs of any High Air Pollution alert system and the low level of benefits clearly indicate that these resources should be re-allocated to efficient pollution abatement strategies. They should particularly be allocated to mandatory actions on clean transportation and fuels and other interventions which need to be part of a comprehensive air quality strategy.

High Air Pollution alert days will not work and will be rejected by an informed public, legislature and government when they understand the implications of the cost-benefit equation.


  1. - last accessed 9/8/10