Proposal for the calculation of the high percentiles of concentrations necessary for the execution of Directive 1999/30/EU
Directive 1999/30/EC demands that we determine the 19th highest hourly concentration value of NO2 occurring within a year. Analysis of data from field measurements and wind-tunnel experiments show, that due to the natural variability of 1 hour mean values of concentrations, one cannot expect good agreement between mathematical model results and measurements. It is also pointed out that very good input data are the absolute requirement for using any model. As these data are usually not available for operational purposes, it is suggested that we use an empirical relationship between the 98th percentile and the 19th highest concentration value of NO2, deduced from measurements. First results are given, but more research is necessary to substantiate this idea and to quantify its accuracy.
Keywords: air pollution, Directive 1999/30/EC, limit value, NO2, percentiles, urban air quality