Dark green dots correspond to concentrations under the WHO reference level (0.12 ng/m3).
Pale green dots correspond to concentrations under the lower assessment threshold (0.4 ng/m3).
Orange dots correspond to concentrations between the lower and the upper assessment threshold (0.6 ng/m3).
Red dots correspond to concentrations above the upper assessment threshold but under the target value of 1 ng/m3.
Dark red dots correspond to concentrations exceeding the target value of 1 ng/m3.

References and footnotes