Nitrogen oxides include:
- nitrogen monoxide (NO) from high temperature combustion phenomena by oxidation of the nitrogen in the air;
- nitrogen dioxide (NO2), which is called secondary pollutant because it mainly comes from atmospheric oxidation of NO.

Their presence on the premises is due to:
- outdoor sources: fireplaces for industry and heating, automobile traffic ;
- indoor sources: gas appliances (cookers, boilers, water heaters, oil heaters) and to a lesser extent, wood or gas stoves and cigarette smoke.

Although experimental studies on animals and humans show actual toxicity of nitrogen dioxide, the results of epidemiological studies are not as conclusive. In fact, pulmonary effects of controlled exposure to high concentrations of nitrogen dioxide are known in humans and animals, but the effect on health of low levels is not as clearly demonstrated in epidemiological studies.

However, asthmatics are a group sensitive to nitrogen dioxide: NO2 exposure leads to impaired lung function and an increase in airway sensitivity to broncho-constrictors.

In order to contain the accumulation of nitrogen oxides in our homes, it is advisable to:

• entrust the installation and maintenance of combustion systems to licensed professionals and use them in accordance with the instructions given by the manufacturer;
• get the boiler checked before the onset of winter by a licensed professional and get it completely overhauled annually;
• check that the flue gases are discharged outside the building and that the chimney is in good condition and not blocked;
• not install a hood connected to the outside in a room where there is also a device connected to a chimney. This may severely affect the working of the device. In this case rather use an air recirculating hood and consult an installer;
• clean the burners on your gas stove regularly (flames of each hole should be blue and short). A well-adjusted flame does not blacken the bottom of the pans;
• use small water heaters and small cooking appliances not connected to the outside only intermittently and for a short time (max. 8 minutes) in sufficiently large and airy rooms (minimum 8 m³ for a cooking appliance and 15 m³ for a small water heater). They are not allowed in bathrooms, bedrooms, living rooms and in studio flats;
• use mobile heaters fuelled with butane, propane or oil only in ventilated areas. Make sure they are fitted with safety devices with atmosphere control;
• never warm yourself with the oven of cooking range (door open), a radiator for camping outdoors, a brazier, a radiator for site use, etc.;
• never operate a generator or a barbecue in a closed area.