What is it?
Nitrogen dioxide is an irritant gas, which at high concentrations causes inflammation of the airways.
When nitrogen is released during fuel combustion it combines with oxygen atoms to create nitric oxide (NO). This further combines with oxygen to create nitrogen dioxide (NO2). Nitric oxide is not considered to be hazardous to health at typical ambient concentrations, but nitrogen dioxide can be. Nitrogen dioxide and nitric oxide are referred to together as oxides of nitrogen (NOx).
NOx gases react to form smog and acid rain as well as being central to the formation of fine particles (PM) and ground level ozone, both of which are associated with adverse health effects..
Sources of NOx Pollution
NOx is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. In areas of high motor vehicle traffic, such as in large cities, the amount of nitrogen oxides emitted into the atmosphere as air pollution can be significant. NOx gases are formed whenever combustion occurs in the presence of nitrogen – e.g. in car engines; they are also produced naturally by lightning.
NOx emissions in the EU -share of emissions by sector group, 2011
The pie chart below shows that road transport and energy production are the greatest sources of NOx emissions in the EU during 2011.
Source - European Union emission inventory report 1990–2011 under the UNECE Convention on Long-range Trans-boundary Air Pollution (LRTAP)
NOx emitted in the City of London
The anticipated relative proportion of emissions of NOx, from vehicles and gas boilers in the City during 2011, is shown in the pie chart below. A very similar picture is predicted for 2015.
Source of NOx in the City, 2011
Source - “City of London Air Quality Strategy 2011-2015”
Health Issues created by NOx
NOx mainly impacts on respiratory conditions causing inflammation of the airways at high levels. Long term exposure can decrease lung function, increase the risk of respiratory conditions and increases the response to allergens. NOx also contributes to the formation of fine particles (PM) and ground level ozone, both of which are associated with adverse health effects.
The impact of nitrogen dioxide on ecosystems
High levels of NOx can have a negative effect on vegetation, including leaf damage and reduced growth. It can make vegetation more susceptible to disease and frost damage. A study of the effect of nitrogen dioxide and ammonia (NH3) on the habitat of Epping Forest has revealed that pollution is likely to be significantly influencing ecosystem health in the forest. The study demonstrated that local traffic emissions contribute substantially to exceeding the critical levels and critical loads in the area. The critical level for the protection of vegetation is 30 µg/m3 measured as an annual average.
NOx also reacts with other pollutants in the presence of sunlight to form ozone which can damage vegetation at high concentrations.
Notes: Critical Level is the threshold level for the atmospheric concentration of a pollutant above which harmful direct effects can be shown on a habitat or species. Critical Load is the threshold level for the deposition of a pollutant above which harmful indirect effects can be shown on a habitat or species.
NOx Level Objectives
Twelve European Member States exceeded one or more of the emission limits set by the EU National Emission Ceilings (NEC) Directive, according to recent official data for 2010 reported to the European Environment Agency (EEA). In some instances the limits were exceeded by significant amounts. The pollutant for which most exceedances were registered was NOx.
The European Union sets Limit Values for a range of pollutants that are considered to be harmful to health and the environment. The European Commission can take action against any Member State if the air quality does not meet the Limit Values throughout its territory.
Read more about the NOx Level Objectives....