Uncertainty assessment of local no2 concentrations

Local nitrogen dioxide concentrations near Rotterdam (Netherlands) were assessed for the year 2010, focusing on the uncertainties and the changes in exceedance of European air quality standards. In the first step of the 2-step assessment method, the background contribution was determined by error-in-variable external drift kriging, where measurements and dispersion model output in the 1987–2003 period were combined. The result was subsequently extrapolated using dispersion model output and an emission scenario for 2010. In the second step, the local traffic contribution was added on the basis of a local generic dispersion model with use of an emission scenario for 2010. This resulted in maps showing local nitrogen dioxide concentrations, upper and lower limits, and probabilities of exceeding the 40 µg/m³ air quality standard. The probabilistic measures were calculated in numbers and translated into words for easier communication. Using this method and scenario we found that within about 100 m from the highways near Rotterdam the mean nitrogen dioxide concentrations are likely to exceed the standard in 2010. The chance of exceeding the standard is unlikely up to 1 km from the highways, where the mean is expected to be below the standard in 2010.