Oxides of Nitrogen

Oxides of nitrogen, mainly nitrogen dioxide (NO2), are formed when air is involved in high temperature combustion (like what happens in power plants and engines). Nitric oxide (NO) is also formed but quickly oxidises to become NO2.

Nitrogen dioxide is bad for human health as it inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis. Long-term exposure increases the likelihood of respiratory problems in children and, along with sulphur dioxide; it leads to the formation of acid rain as outlined above.

 
NO2 2019 Map

Levels of Nitrogen Dioxide are strongly related to traffic emissions, this map produced by the EPA (2019) shows higher concentrations of the gas around the M50, with levels above the EU limit of 40 μg/m3.


The graph above shows annual average nitrogen dioxide concentrations recorded in urban and rural zones from 2003 to 2019. Zone A is Dublin, Zone B is Cork, Zone C represents 21 large towns and Zone D is the remainder of the country. There has been little change in rural levels during these years. Although most ambient levels have dropped recently in urban areas, they still remain close to the annual limit value. The higher levels in cities are due to emissions from vehicles. Levels in Dublin breached EU limits in 2019. If this trend continues and standards are breached, traffic may have to be restricted in some areas of city centres.
   


The graph below shows trends in Ireland's NOx emissions since 1990. Transport is the principal source of NOx emissions, contributing 40.6% of the total in 2018. Agriculture is the second biggest source, mainly from synthetic fertilizer application and emissions from grazing animals (urine and dung) (EPA, 2020). 


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