Carbon Monoxide: Definition, Composition and Risks for Health

Carbon monoxide (CO) is a colourless, odourless and tasteless gas that is highly toxic to humans and animals. It is produced from the incomplete combustion of carbon-containing fuels and is emitted from sources like vehicle exhaust, faulty furnaces, and burning biomass.

The chemical properties of carbon monoxide make it dangerous. Its molecule has one carbon atom bonded to one oxygen atom, with the carbon atom having two remaining bonding sites occupied by a pair of electrons. This allows carbon monoxide to bind over 200 times more tightly to haemoglobin in blood than oxygen, displacing oxygen and reducing the blood's ability to transport oxygen around the body.

Exposure to carbon monoxide poses significant health risks. At low concentrations, it can cause fatigue, headaches, nausea, dizziness and impaired vision. Higher concentrations can lead to confusion, loss of consciousness, coma and death. Foetuses, infants, elderly people and those with heart or respiratory conditions are most vulnerable to CO poisoning. Symptoms are often described as 'flu-like' making CO poisoning difficult to diagnose without a carboxyhaemoglobin test.

Environmentally, carbon monoxide contributes to air pollution both locally and globally. As an air pollutant, it produces tropospheric ozone which impacts human health. It also acts as a greenhouse gas, trapping heat in the atmosphere and contributing to climate change. Measures to reduce CO emissions including transitioning to cleaner energy sources will have co-benefits for both human health and the environment.

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What is Carbon Monoxide?

Carbon monoxide (CO) is a toxic gas that is classified as an air pollutant. It is produced from the incomplete combustion of carbon-containing fuels and materials when there is not enough oxygen present for full combustion. Sources of carbon monoxide emissions include vehicle exhaust systems, faulty furnaces, burning biomass, and industrial processes.

The chemical characteristics that define carbon monoxide are that it is a colourless, odourless and tasteless gas. Its molecule is composed of one carbon atom bonded to one oxygen atom, with two lone pairs of electrons occupying the remaining bonding sites on the carbon atom. This gives carbon monoxide very different chemical properties compared to oxygen. It allows carbon monoxide to bind tightly to haemoglobin in blood, reducing the blood's capacity to transport oxygen around the body.

Carbon monoxide's lack of colour, smell and taste makes it undetectable to humans. This makes carbon monoxide a very dangerous air pollutant, as people cannot rely on their senses to detect toxic levels before harmful health effects occur. Understanding the chemical characteristics of carbon monoxide helps explain why it poses such a significant health risk.

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What is the Composition of Carbon Monoxide?

The molecular structure of carbon monoxide is simple, with just one carbon atom bonded to one oxygen atom. The carbon atom has two remaining bonding sites occupied by lone pairs of electrons. This gives carbon monoxide the chemical formula CO.

Carbon monoxide forms when there is insufficient oxygen for the full combustion of carbon-containing fuels and materials. It is produced from both natural and human-induced processes. Incomplete combustion occurs when carbon in fuels reacts with oxygen to form CO rather than CO2.

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What are the Major Sources of Carbon Monoxide?

The major anthropogenic (human-caused) sources of carbon monoxide include:

• Vehicle exhaust - Petrol and diesel engines produce CO from inefficient combustion. Levels are higher in traffic congestion.
• Industrial processes - Metallurgy, petroleum refining and pulp/paper manufacturing emit CO from burning fuels.
• Residential heating - Malfunctioning furnaces, water heaters and wood-burning stoves release CO.

Natural sources also emit substantial quantities of CO:

• Wildfires - Large amounts of CO are emitted from the burning of vegetation in bushfires.
• Volcanic eruptions - Magma releases CO when it comes to the surface during volcanic activity.
• Oxidation of methane - Methane reacts with hydroxyl radicals in the atmosphere to produce CO.

Understanding where CO comes from allows mitigation strategies to be targeted at major emission sources.

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What are the Harmful Effects of Carbon Monoxide on Humans?

Exposure to elevated levels of carbon monoxide poses significant health risks. At lower concentrations, symptoms can include headaches, dizziness, weakness, upset stomach, confusion and impaired vision and coordination. Higher exposure can lead to loss of consciousness, coma and even death.

Common symptoms of carbon monoxide poisoning include:

• Mild exposure: Headaches, nausea, fatigue, flu-like symptoms
• Moderate exposure: Severe headaches, dizziness, confusion, fast heart rate
• Extreme exposure: Convulsions, unconsciousness, respiratory failure, death

Prolonged exposure to low levels can also have long-term health effects including increased risk of heart disease, brain damage and cognitive impairments. Foetuses, infants, elderly and those with anaemia or heart/respiratory conditions are most at risk.

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What are the Laws to Reduce Carbon Monoxide in Air?

The World Health Organization sets guidelines limiting carbon monoxide levels. In Australia, the National Environment Protection Measures set a maximum ambient CO level of 9.0 ppm averaged over 8 hours.

Policies targeting CO reduction in Australia include:

• Vehicle emissions standards to reduce exhaust from petrol and diesel engines.
• Improved efficiency standards for wood heaters and industrial combustion processes.
• Monitoring of air quality in cities to identify and mitigate hotspots.

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What is Australia Doing to Prevent Carbon Monoxide Exposure?

Australia has implemented a range of policies and regulations aimed at reducing carbon monoxide (CO) levels in the air. These efforts target both anthropogenic and natural sources of CO emissions.

For vehicle emissions, Australia's standards require petrol vehicles to have catalytic converters installed. These convert toxic gases like CO into less harmful ones. There are also national diesel vehicle emission standards in place. Many existing diesel vehicles are being retrofitted with particulate filters to reduce particulate matter and CO in exhaust fumes.

For residential wood heaters, new standards have been introduced requiring all new heaters sold to meet strict efficiency and emission limits. There are government schemes helping households replace old, highly polluting wood heaters with new, cleaner models that produce less CO.

Industrial emissions of CO are regulated through the National Pollutant Inventory. Facilities exceeding reporting thresholds must monitor and report CO discharges enabling targeted mitigation. More efficient combustion processes and pollution control devices help lower industrial CO emissions.

When large bushfires occur, alerts are issued warning about potentially hazardous CO levels in smoke. Public health messaging provides advice on reducing exposure. Post-fire programs assess impacts and implement strategies to reduce risks from future events.

Ongoing air quality monitoring in major cities measures ambient CO concentrations, informing policy development and allowing risk communication to the public. High pollution alerts trigger health warnings and advice to curb activities that increase exposure.

Combined, these policies and initiatives aim to lower CO emissions from Australian sources and minimise harmful population exposures through awareness and reduced activity when risks are elevated.