Fact file
Nitrogen oxides (NOx) are made up of a mixture of nitric oxide (NO) and nitrogen dioxide (NO2). They are produced during combustion phenomena by the high-temperature oxidation of nitrogen (N2) in the air and, to a lesser extent, of the nitrogen contained in fuels. The majority of these emissions come in the form of nitric oxide (NO), which has a short lifespan in the atmosphere and can oxidise to nitrogen dioxide (NO2). Monoxide and nitrogen dioxide thus form a dynamic equilibrium and that is why they are studied together.
NO2 is used for the calculation of the Belgian air quality index, BelAQI
Origin of pollution
Anthropogenic emissions come mainly from combustion processes and the main sources of nitrogen oxides are energy-intensive sectors. In Wallonia, the transport sector is responsible for half of anthropogenic emissions, compared with approximately 30% for the industrial sector. In urban areas, where traffic emissions are predominant, the concentrations of nitrogen oxides in the air can even be considered to be characteristic of traffic density and conditions.
Health effects
At the concentrations usually found in air, nitric oxide is not considered toxic.
Nitrogen dioxide is an oxidant and an irritant to the respiratory tract, especially the bronchi. People suffering from asthma or chronic respiratory pathologies form the at-risk population when it comes to this pollutant. In children, it increases sensitivity to pathogens.
Epidemiological studies have shown that an increase in nitrogen dioxide concentrations was accompanied in particular by an increase in the number of deaths from cardiovascular causes.
In addition to its direct impact on health, nitrogen dioxide is a precursor to ozone (see ozone fact file). In addition, in the atmosphere, it can turn into nitric acid and react with ammonia NH3 to form secondary aerosols.
Environmental impact
Nitrogen oxides participate in the acidification of the environment and their fallout promotes environmental eutrophication. Indeed, the nitrogen supply exceeds the absorption capacity of certain ecosystems and creates an imbalance by favouring certain species with, consequently, an exhaustion of biodiversity.
As a precursor to ozone, nitrogen dioxide has an indirect impact, through the formation of ozone, on crop yields.
The situation in Wallonia
Nitrogen oxides participate in the acidification of the environment and their fallout promotes environmental eutrophication. Indeed, the nitrogen supply exceeds the absorption capacity of certain ecosystems and creates an imbalance by favouring certain species with, consequently, an exhaustion of biodiversity.
As a precursor to ozone, nitrogen dioxide has an indirect impact, through the formation of ozone, on crop yields.
Measurement methods
Nitric oxides are measured continuously and in real time using monitors using the principle of chemiluminescence.
Find out more :http://www.awac.be/index.php/2017-03-28-09-19-01/emission-de-nox
