The graph is based on the annual mean concentration values for each Member State; the boxes present the range of
concentrations at all stations types (in μg/m3) officially reported by the EU Member States and how the concentrations relate
to the limit value set by EU legislation (marked by the red line).
The diagram indicates the lowest and highest observations, the means and the lower and upper quartiles. The lower quartile
splits the lowest 25 % of the data and the upper quartile splits the highest 25 % of the data.

References and footnotes