Air and Noise

Nitrogen Dioxide Air Pollution

The "Nitrogen Dioxide Air Pollution" fact sheet analyses the progress towards the objectives imposed for this pollutant across the country, in order to safeguard the protection of human health.
Description: 

Nitrogen dioxide (NO2) is mainly produced by industrial and automotive combustion and the oxidation of nitrogen fertilizers, with potential health effects, which can result in increased susceptibility to respiratory diseases, especially in children, and in lung function, especially in asthmatics.

The determination of the NO2 annual average, resulting from the concentrations recorded in the monitoring stations in each zone, allows the respective comparison with the limit value (LV) stipulated in the legislation for the protection of human health.

The measured NO2 levels differ according to the type of station, whether by the surroundings (rural, suburban or urban) or by the influence of the pollution source (traffic, industrial or background). The analysis of the aggregated hourly average values according to this typology, allows the identification of the evolution trend according to the nature of the emission source, enabling a more optimized targeting of action for its reduction.

For this assessment, all stations with a measuring efficiency greater than 75% are used. For stations covered by the indicative measurement assessment strategy, measurements with an efficiency greater than 14% are also used.

This fact sheet concerns mainland Portugal, the Autonomous Regions of Madeira and the Azores and will be updated annually.

 

Objectives and targets: 
  • Ensure compliance with the EU-wide targets for ambient air quality, which aim to avoid, prevent or limit the harmful effects of air pollutants on human health and the environment;
  • Measure ambient air quality across the country, with a special focus on urban centres;
  • Preserve air quality where it is good and improve it in other cases;
  • As targets, the limit values set forth in the legislation are not to be exceeded  (Decree-Law no. 102/2010):
    • limit value for the average hourly concentration of 200 μg/m3 of NO2, not to be exceeded more than 18 times per calendar year;
    • Limit value for the average annual NO2 concentration of 40 μg/m3.
Progress analysis:

Exceedances to the annual threshold limit value of NO2 in areas and agglomerations monitoring them (background, traffic and industrial stations in 2016 and 2017)

Notas: (a) - Agglomeration (1) - Area with measurement efficiency <75 % in 2016 (2) - Areas and agglomerations for which suficient information was not obtained for assessment using air quality models in 2016 (3) - Areas and agglomerations for which information was obtained for assessment using air quality models in 2017
Source: APA, CCDR Norte, CCDR Centro, CCDR Lisboa e Vale do Tejo, CCDR Alentejo, CCDR Algarve, DRA Madeira, DRA Açores, 2018

The exceedances to the annual limit value (VL) in large urban agglomerations persist, with an increase in the levels measured in the agglomerations of the Lisboa Norte Metropolitan Area (from 57 μg/m3 in 2016 to 60 μg/m3 in 2017). The Northern Region agglomerations, maintained the exceedance of the VL, despite a large decrease in the average annual concentration of the Porto Litoral agglomeration (from 75 μg/m3 in 2016 to 54 μg/m3 in 2017). This situation may be related to the reduction in the measuring efficiency of the station monitoring this zone. The Entre Douro e Minho agglomeration maintained the level of exceedance to the VL (55 μg/m3).

The intensive use of the car in day-to-day commuting is maintained, and since the source of this pollutant is strongly associated with traffic emissions, which is boosted by the acknowledged deviation of the most demanding EURO standards applied to vehicles under real driving conditions, it is influencing the levels measured in large urban agglomerations.

It is also noticeable that in the remaining zones and agglomerations the magnitude of the measured levels was maintained, but in the Oeste, Vale do Tejo e Península de Setúbal, there was a significant increase of the measured levels of NO2, compared to 2016 (from 6 μg/m3 to 19 μg/m3).

The hourly VL of 200 μg/m3, not to be exceeded more than 18 times in one year, was significantly overtook in the AML Norte, Avenida da Liberdade station, with 74 exceedances, a situation that had not occurred since 2012.

 

Evolution of the average annual concentration of NO2 by type of station

Source: APA, CCDR Norte, CCDR Centro, CCDR Lisboa e Vale do Tejo, CCDR Alentejo, CCDR Algarve, DRA Madeira, DRA Açores, 2018

The trend analysis of the annual average values of NO2 per type of station shows a slight growth trend since 2014 in urban and suburban background stations, where the most significant population exposure to this pollutant occurs.

For the remaining typologies, there is a maintenance trend in the magnitude of the measured concentrations.

In the QualAr information system, measurements made at all the network stations and for all pollutants are available online and in real time. However, it should be noted that this data is provisional and for informational purposes only. Validated data is available from October of the following year.
 

Last update: 
Monday, 29 October, 2018
More information at: 

Portuguese Environment Agency - www.apambiente.pt
QualAr: National information system on air quality - qualar.apambiente.pt