Fact file

Carbon monoxide (CO) is a colourless, odourless gas. It is produced during the incomplete combustion of materials containing carbon, an intermediate stage before the final stage of oxidation, which yields carbon dioxide (CO₂).

In a domestic environment, it causes frequent and sometimes fatal poisoning when the oxygenation of a home (stove, water heater, etc.) is insufficient, either due to a poor supply of fresh air or poor smoke extraction.

Naturally present in the atmosphere, it is also produced by many human activities, such as heating, transport and industry.

Origin of pollution

Carbon monoxide emissions are linked to combustion phenomena. In Wallonia, the residential sector is the largest emitter of carbon monoxide, with a share of 44% (in 2014). Transport and industrial sectors rank second and third, with 28% and 20% of emissions respectively. Between 2000 and 2014, emissions linked to the industrial sector fell by 94%, with a decrease of 69% for the transport sector. Over the same period, emissions from the residential sector have remained fairly stable.

Health effects

When it is inhaled, carbon monoxide enters the bloodstream and decreases the amount of oxygen carried by the blood. CO has, in fact, the capacity to displace the oxygen fixed in haemoglobin (which transports oxygen to the tissues) to form carboxyhaemoglobin (very stable) with the consequence of a reduction in the oxygenation of the tissues by reduction of the availability of haemoglobin able to fix oxygen. The most affected organs are tissues with high oxygen consumption, such as the brain, heart, muscles, or the fetus during pregnancy. The effects are proportional to the amount of carboxyhaemoglobin in the blood: cardiovascular disorders, neurological effects, headaches, dizziness and even, in extreme cases, coma and death.

For the protection of the population, including groups at risk, the World Health Organization recommends not to exceed a level of carboxyhaemoglobin of 2.5 to 3%.

Environmental impact

Carbon monoxide can participate in the ozone formation mechanism. In the presence of photochemical oxidants, it oxidises to carbon dioxide and thus contributes to the greenhouse effect.

The situation in Wallonia

In Wallonia, carbon monoxide is a pollutant which poses no problem concerning compliance with the European standard in force. Likewise, carbon monoxide concentrations are well below World Health Organization guide values.

Measurement methods

Carbon monoxide is measured continuously and in real time using monitors employing a NDIR (non-dispersive infra-red) technique.