Air quality fact sheet
Department of the Environment and Heritage, 2005
Biomass burning is the combustion of organic matter. Burning can be from natural or manmade fires. Examples are the burning of crop stubble, forest residues and vegetation burnt for land clearing. Information about smoke from the combustion of wood in woodheaters is available in our factsheet on woodheaters and woodsmoke.
'Prescribed burning' is a term used to describe the deliberate use of fire for management purposes. Fire is used as a tool to reduce the risk of wild fires by clearing out highly flammable leaves and branches shed by native vegetation in parks, reserves, on farms and bush blocks.
Biomass burning is a major source of many air-borne particles and trace gases that influence the concentration of ozone at ground level. (See our fact sheet on ozone.)
When a fire is first lit the moisture is driven off. As it gets hotter, chemical reactions occur that produce gases. Smoke contains the unburnt portion of these gases. Smoke is a complex mixture of many chemicals including carbon dioxide, water vapour, carbon monoxide, particles, hydrocarbons, nitrogen oxides and thousands of other compounds. The actual composition of smoke depends on the type of wood and vegetation being burnt, the temperature of the fire and the wind conditions.
Particles from smoke tend to be very small – less than one micrometer in diameter. In comparison, a human hair is 70 micrometers in diameter. (See our fact sheet on particles.)
Biomass burning also produces carbon monoxide. (See our fact sheet on carbon monoxide.) The concentrations of carbon monoxide are highest when the fire is smouldering. Benzene and formaldehyde are present in smoke but at much lower levels than particles and carbon monoxide.
Thick smoke from biomass burning does not necessarily cause health problems for everyone exposed to it. Most healthy people recover quickly from exposure to smoke and do not suffer long-term effects. There are a number of factors that determine whether exposure to smoke results in health problems: the concentrations of the air pollutants, the length of exposure, age, individual susceptibility and whether or not there is pre-existing lung or heart disease.
Smoke has a range of health effects – from eye and respiratory tract irritation to serious disorders such as breathing problems, bronchitis, increased severity of asthma, cancer and premature death. The very fine particles in smoke can go deep into the lungs and fine particles, by themselves or in combination with other air pollutants, can make pre-existing diseases of the heart and lungs worse. Where there is short-term exposure to smoke, the particles are the most significant threat to public health.
High levels of carbon monoxide are poisonous to humans. However, carbon monoxide arising from smoke events does not usually reach levels that pose a risk to the general population, although firefighters and people with heart disease can be at risk.
Most healthy people, including children, recover quickly from exposure to smoke and do not suffer long-term consequences. However, certain sensitive groups can experience more severe short-term and chronic effects. It appears that the same population groups that are susceptible to particles in cities are also susceptible to particles from biomass burning. These groups are: people with asthma and other respiratory disease, people with cardiovascular disease, children and the elderly. Pregnant women and unborn children are potentially susceptible, given that smoke from biomass burning contains many of the same compounds found in cigarette smoke.
Bushfires are a part of the Australian way of life. All States and Territories have experienced catastrophic fires over the years and observed the adverse effects on air quality as one of the consequences.
Smoke from prescribed burning is also common in Australia and the levels of smoke from this source vary depending on the nature of the vegetation and the extent of the fire. Smoke from prescribed burning can be minimised if fires are lit at the right time of year and managed correctly. Smaller hotter fires are preferred, as this minimises air pollution.
Fire is also a common land management practice in many agricultural areas of Australia where it is used to burn the by-products of some agricultural crops, eg sugar cane waste, wheat or rice stubble and forest residues. Extensive areas of crop residues are burnt each year across Australia which can create large amounts of smoke for extended periods.
There are many initiatives to reduce the use of fire in agriculture. Alternatives to burning are now encouraged because they have less impact on air quality and are more environmentally sustainable. Wheat stubble is used to produce straw board or it can be returned to the soil to reduce erosion and moisture loss. Ethanol production from a range of agricultural waste products such as wheat and rice straw and sugar cane waste is in the early stages. Land managers now routinely use tools to model dispersion of smoke in the atmosphere. This helps to manage and predict air quality outcomes from biomass burning in their areas.
Related publications are available from the Community Information Unit of the Department of the Environment and Heritage, phone 1800 803 772. These include Air Quality fact sheets on: lead, nitrogen dioxide, carbon monoxide, ozone, particles, sulfur dioxide, air toxics; woodheaters and woodsmoke; and National Standards for Criteria Air Pollutants in Australia.
See also our website at Air quality.