Nox Plotter (Expert mode)
The NOx plotter by Forschungszentrum Jülich uses hourly values of nitrogen oxide concentrations (NO: nitrogen monoxide, and NO₂: nitrogen dioxide) from the German air quality monitoring network. You can choose any station from this network and the web tool will calculate if the legal air quality threshold of 40 µg/m³ (annual mean value) has been exceeded, and by how much the emissions of nitrogen oxides must be reduced to meet the target value. The expert mode displays the data curves which are used for this calculation. To get a simpler graphical display of the results, please change to the standard mode.
The legal limit value of 40 µg/m³ NO₂ as annual mean is only exceeded at stations with a road traffic pollution signature. At these sites, nitrogen oxide emissions are dominated by road traffic and in particular by diesel combustion in passenger and transport vehicles. Therefore it is only possible to reduce NO₂ concentrations at these locations by reducing vehicle traffic emissions. It is not straightforward to estimate the required emission reduction based on the measured NO₂ concentration exceedance, however. Vehicle exhaust contains both NO and NO₂. Typically, the NO₂ fraction in the exhaust is only ~15% while the remaining NOx is emitted as NO. NO, NO₂, and ozone react with each other in an atmospheric chemical reaction cycle. Within minutes, NO reacts with ozone from the background air to form NO₂. During daytime NO₂ can photolytically dissociate to yield the NO and ozone back (see for example Tropospheric ozone).
One consequence of this chemical reaction cycle is the non-linearity of the relation between the emitted NOx and the measured NO₂ concentration. The more NO is contained in the air, the lower is the fraction of this NO that is converted to NO₂. This results in the necessity to apply over-proportional reductions of the NOx emissions, i.e. the higher the NO₂ exceedance, the more extra NOx emissions have to be avoided. The exact value can be obtained through the Jülich NOx calculator. It works by plotting the hourly measurements of NO₂ versus the sum of the NO and NO₂ concentrations. These curves are shown in the expert mode of the NOx plotter. In case you cannot find your favorite measurement location in the station dropdown list it is very likely that NO₂ concentrations at this station are measured through laboratory analysis of filter samples. Since the NOx plotter works with hourly data of NO and NO₂, it cannot make use of such measurements.
Usage:
Just enter the name of a city or a street address in the location field and select a measurement station near you. Click on “Create Plots” and you will obtain the graphical results.
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