Carbon monoxide

How carbon monoxide gets in the air and its effects on health. Usual levels in New Zealand. Standards and guidelines values to protect human health.

Chemical formula and description

The chemical formula for carbon monoxide is CO.

Carbon monoxide is a colourless, odourless and tasteless gas.


The most common source of carbon monoxide is human activities, such as the incomplete combustion of fossil fuels (eg, petrol in cars, and wood and coal burnt in home heating).

Carbon monoxide is also produced by natural processes (eg, volcanoes, fires and metabolism of organisms). 

Effects on health

When you breathe in carbon monoxide, it attaches to haemoglobin molecules in your bloodstream, which carry oxygen around your body to your tissues, and reduces the amount of oxygen your body tissues receive. This can have adverse effects on your brain, heart and general health.

Low exposure to carbon monoxide can make you feel dizzy, weak, nauseous, confused and disoriented and can also reduce your performance while doing exercise. The higher the level of carbon monoxide in your blood stream, the worse the effects. So at very high levels coma, collapse, loss of consciousness and death can occur.

Groups most sensitive to carbon monoxide

  • middle-aged and elderly people with heart disease
  • foetuses of pregnant mothers.

Standards and guideline values to protect health

The national environmental standard for carbon monoxide is 10 mg/m3 as an 8-hour average. 

The national ambient air quality guideline for carbon monoxide is 10 mg/m3 as a 1-hour average.

Usual levels in New Zealand

Levels of carbon monoxide have significantly reduced over the past 15 years and are generally well below the ambient standard.

Areas where carbon monoxide may affect health

Carbon monoxide concentrations are generally highest around congested roads. It can be an urban-wide problem when winter smog traps carbon monoxide discharged from domestic fires and vehicles during temperature inversion conditions.