Homepage MNP Homepage CBS Homepage WUR

Relation between figures for emissions and environmental quality

Air quality measurements from the National Air Quality Measurement Network (LML) make it possible to conduct an independent validation test for trends in emissions and the concentrations calculated on that basis.

Both the emissions and concentrations of volatile organic compounds (VOC), nitrogen oxides (NOx), particulate matter, benzene and sulphur dioxide (SO2) appear to be falling.
  • The concentrations of VOC, NOX and benzene in busy streets are matching urban traffic emissions. It is only in recent years that the concentrations have been falling faster that the reported emissions.
  • This also applies to transboundary VOCs, a group of substances that contribute to ozone creation.
  • In the case of SO2, emissions and concentrations are declining to the same extent. The peaks in the concentration are caused by heightened concentrations during frosty spells.
  • With particulate matter, it is not as straightforward to make the link between emissions and concentrations and the comparison is therefore less reliable. Concentrations would appear to be dropping less quickly than emissions in North-West Europe. This may in part be attributable to the very large reductions in emissions in East Germany since they make a more limited contribution. Furthermore, there is a possible effect caused by particulate matter that is only formed in the air from gases. These formation processes are not always proportionate to emissions.

Ammonia concentrations follow the fall in the emissions trend, 1993-2001


Since 1993, the concentration of ammonia in the air has been measured at eight sites in the National Air Quality Measurement Network. Changes in the concentration over time were used to monitor the efficacy of the reduction measures (figure 2). The average concentration before 1997 was fairly constant at approximately 11 µg/m3 and fell after 1997 to approximately 8 µg/m3. Between 1993 and 2001, emissions fell by approximately 40%. Emission fluctuations are only roughly reflected in concentration fluctuations since the latter are partly subject to the influence of meteorological conditions. These conditions can vary considerably from year to year and may mask the trend in the emissions. These influences have not yet been analysed for the entire period.
Because the eight monitoring sites for ammonia in the National Air Quality Measurement Network only cover part of the Netherlands, check measurements were carried out at 159 locations. It emerged that there was a close spatial overlap between emissions and concentrations.
Previous Environmental Balances from the RIVM concluded that the calculated reduction in the emission of ammonia was not apparent from the measurements of ammonia concentrations during the period 1993-1997. This phenomenon was referred to at the time as the ammonia gap. On the basis of the longer series of measurements available to us now, it is possible to conclude that this phenomenon is a thing of the past. There is still an absolute difference between the measured ammonia concentrations and the concentrations calculated on the basis of the emission data (see below). The calculation of ammonia deposition for the Netherlands is adjusted for this difference.

Comparison of measured and calculated concentrations for ammonia, 1993-2001


Although the reduction trend for ammonia emissions is now reflected in measured concentrations, there is still an absolute difference of approximately 30% between measured and calculated concentrations of ammonia (figure 3). This difference can be explained by reference to the under-estimation of emissions and incorrect model parameters. There are indications that the model parameters in particular result in an over-estimation of dry deposition rates for ammonia. Research has been initiated into both areas.

Comparison of measured and calculated concentrations for particulate matter


Concentration calculations using dispersion models described, until recently, approximately half of the measured regional concentrations of particulate matter. This was largely due to the fact that natural sources were not adequately accounted for in the models. A study by Visser et al. (2001) established a reasonably accurate balance for the origin of particulate matter.

References


  • Visser, H. E. Buringh and P.B. Breugel (2001). Composition and origin of airborne particulate matter in the Netherlands. RIVM (report 650 010 029), Bilthoven.

Relevant sections and indicators in the Environmental Data Compendium
This page was last changed on November 22, 2005  (version 01).