A Status Report to the Community: Living Cities – Air Toxics Program

Environment Australia, June 2002
ISBN 0 6425 4738 6


Indoor and outdoor air

The quality of indoor air is influenced by the quality of outdoor air, how much outdoor air gets in, and by the amount of pollution that is emitted from indoor sources. The relatively free movement of air means that, potentially, any air pollutant originating outdoors-for example from cars, factories or fires-can move to become a problem indoors.

Despite this close relationship between indoor and outdoor air quality, indoor air and outdoor air have traditionally been considered separately when assessing the effects of exposure to air pollutants, and for introducing controls to reduce levels of pollutants. However, it is becoming more common to consider both indoor and outdoor air when developing air quality controls.

For the purposes of control, indoor air can be defined as any non-industrial indoor space where a person spends a period of an hour or more in any day. This can include the air space in the office, classroom, motor vehicle, shopping centre, hospital and home.

Air pollutants

There are two categories of air pollutants-criteria pollutants and air toxics.

Criteria (or common) pollutants

There are six criteria or common air pollutants that are known to have harmful effects on our health. They are carbon monoxide, nitrogen dioxide, ozone1, sulfur dioxide, lead and particles. These criteria pollutants are used to give an overall indication of Australian air quality. They have been extensively studied and monitored and Australia has set national standards for them in our outdoor (or ambient) air.

Air toxics

Air toxics are sometimes referred to as 'hazardous air pollutants'. They include several types of chemicals, including metals and metal compounds, polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and persistent organic pollutants. Air toxics usually occur at lower concentrations than criteria pollutants.

The Living Cities – Air Toxics Program defines air toxics as 'gaseous, aerosol or particulate pollutants that are present in the air in low concentrations with characteristics such as toxicity or persistence so as to be a hazard to human, plant or animal life'.

Air toxics play an important role in smog formation and, in certain circumstances, they can be a significant air pollution problem. Sources of air toxics include motor vehicle emissions, the products of burning fuels and materials such as paints and adhesives in new buildings.

Air toxics have been less studied than the criteria pollutants and their harmful effects at likely ambient exposure levels are less well established. However, air toxics have the potential to cause serious harm to human health and the environment. For this reason, the Commonwealth, States and Territories have been working to assess the risks posed by these pollutants.

Health effects of air pollutants

People respond to air pollutants in different ways. Air pollution has been associated with health effects that can range from serious conditions like asthma, allergic responses and increased risk of cancer to more general symptoms such as sore throat, headache, irritated eyes and running nose.

Some effects can show up years after exposure has occurred, after long periods of exposure, or after repeated exposures. Other effects are more immediate. Studies in Australia have found that where buildings fail to meet ventilation standards occupants can experience headaches, drowsiness and irritability.

Certain groups of people are particularly sensitive to pollutants. Sensitive groups include newborn babies, young children, the elderly, heart patients, people with bronchitis, asthma, hay fever and emphysema, and smokers. Most asthmatics have allergies, and many allergy-causing agents (for example dust mites, fungi and insects) are important biological pollutants of indoor air.


1  Ozone is a secondary pollutant. It is formed from the reaction of nitrogen oxides and volatile organic compounds. Ozone is often used as a measure of photochemical oxidants found in smog.

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