Figure A2.4: Summary of method for determining compliance with the NO2 standard
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Notes: For NO2 at a receptor site using information from local NOx emissions.
Text description of figure
This figure is a flow diagram of the two methods for estimating NO2 concentrations from modelled or measured NOx at a receptor location.
The first method is the total oxidation method. This method uses emissions, meteorological and topographical data to predict NO2 concentrations using dispersion modelling (by assuming all NOx is oxidised to NO2). It assumes background concentrations of NO2 are close to zero - if they are not, the second method (ozone-limiting) is recommended as a way forward. The total oxidation method is very conservative - if predicted NO2 concentrations are in compliance (i.e. within national environmental standards) then the results may be considered robust. If predicted NO2 concentrations are not in compliance, however, the second method (ozone-limiting) is recommended as a way forward.
The second method is the ozone-limiting method (which assumes 10% NO2 in NOx emissions). If predicted NO2 concentrations are in compliance (i.e. within national environmental standards) then the results may be considered robust for most urban/suburban sites. If predicted NO2 concentrations are not in compliance, monitoring may be necessary. Cases where monitoring may be necessary include industrial or congested traffic locations.
