Indoor air pollutants

Environmental tobacco smoke

ETS is a complex mixture that includes some carcinogens and respiratory irritants such as sulphur dioxide, formaldehyde and ammonia.

Formaldehyde

Formaldehyde, a pungent gas, is found in buildings with high quantities of particleboard, fibreboard and plywood (for example, mobile buildings and caravans). It is found in many households and offices in wood-based panels, furniture, glues, dyes, permanent-press clothes, markers, paints and cigarettes.

Nitrogen dioxide and carbon monoxide

These gases are present indoors where unflued gas appliances and wood stoves and heaters with indoor leaks are used.

Volatile organic compounds

VOCs cover a broad spectrum of organic compounds, ranging from about 20 to several hundred in any given sample of indoor air. They are found in new buildings and cars (usually for the first 6 to 12 months following construction).

VOCs are released from most materials, whether synthetic or natural. Highest emissions occur when products are new, and especially if the products are applied wet, such as paints, adhesives or sealants. Long-term emissions, greater than several months, occur from thick materials such as plastic floor coverings and furniture.

Cleaning agents and office equipment are some other indoor sources of VOCs. High indoor VOC levels have been observed in new or renovated buildings and houses with attached garages. Some wool carpets have also shown to produce VOCs.

VOCs are generally present in indoor air at concentrations greater than outdoor air. However, concentrations in homes and offices are generally much lower than in industrial buildings.

Levels of indoor pollutant

Within buildings there are many items, appliances and activities that emit air pollutants. Some air pollutants in buildings come from outdoors. Many outdoor pollutants do not remain airborne when they enter buildings because they become attached to indoor surfaces (called a ‘sink process’) from which they may or may not be later released. Potentially, indoor air pollutants can greatly exceed outdoor levels. It is important that people with asthma consider this when they seek to use their homes or other buildings as refuges from the effects of outdoor pollution.

Typical ratios for levels of pollutants indoors to outdoors are presented in the following table and show the importance of indoor pollutant sources.

Table 3 Levels of pollutants indoors to outdoors

(Note: Additions to Table 3 only available on this website)

Pollutant	Indoor/outdoor ratio of pollutant levels (range low to high)	Comment
Sulphur dioxide	0.1:1 to 1:1.0	Lowest ratios observed in winter when ventilation rate minimised

Sulfates, nitrates	0.5-1.0	Homes with gas stoves can exhibit nitrate ratio ~ 7

Ozone	0.1:1 to 0.7:1	No indoor sources at time of studies

Nitrogen dioxide	Approximately 1:1 (no unflued gas appliances) >1:1 to 5:1 (with unflued gas appliances)	~1 in absence of indoor sources; >1 if gas appliances present

Total Particulate Matter	0.1:1 to 1:3.5	Dependent on ventilation and indoor activities emitting particles (ratio 0.1-1.0 if no activities)

Particles	0.1:1 to 5:1 (depending on indoor particle generation)	High ratios associated with tobacco smoke

Carbon Monoxide	1.0 1.2:1 to 1:5.8	Long-term average in absence of indoor sources Buildings with gas stoves, heaters or smoking

Formaldehyde	5:1 to 30:1	Related to indoor products emitting formaldehyde

VOCs	2:1 to 100:1 (highest ratios in first few months after construction)	Related to indoor products emitting VOCs

In Australia, the National Health and Medical Research Council provides advisory goals for indoor air pollutants.
See Ambient air quality goals recommended by the National Health and Medical Research Council.

The impact of indoor emissions on air quality depends directly on ventilation and air mixing. Traditionally, ventilation rates have been set at levels sufficient to prevent stuffiness and odours from occupants, not to remove indoor emissions. This practice, together with recent efforts to conserve energy, has led to a situation in developed countries where the rate of exchange of indoor and outdoor air has been reduced, particularly in colder climates. Under such conditions, even low emission rates in houses can result in concentrations of indoor pollutants at levels of concern.

Air quality standards

Studies on indoor air quality in Australian buildings have established that people with asthma are likely to experience asthma symptoms where the goals for indoor air pollutants have been exceeded. For example:

Nitrogen dioxide levels in buildings with unflued gas appliances are estimated to exceed the National Environment Protection Measure (NEPM) standard set by the National Environment Protection Council in 1998.
Levels of particles (PM10) in most buildings where there is tobacco smoking or wood heating are likely to exceed the NEPM standard.
Formaldehyde levels in new homes using reconstituted wood-based panels (particleboard, medium density fibreboard, plywood) and in new and established mobile buildings (caravans, mobile homes, offices) have been found to exceed the National Health and Medical Research Council (NHMRC) indoor air goal.
Levels of VOCs in new and renovated buildings and new cars have been found to exceed the NHMRC goal, decreasing initially, then increasing, but not reaching goals for several weeks to months.

For more information see:
WHO. Air quality guidelines for Europe. Updated version. Geneva: World Health Organization, 2001.
Available at http://www.euro.who.int/document/e71922.pdf