The graphs are based on the annual mean concentration values; they present the range of concentrations at all station 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.
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Around 10 million pairs of usable spectacles are discarded each year in Europe and North America. These can be used to help people in the developing world to afford glasses. Most opticians now act as collection points for old glasses, so drop yours off and give them a new lease on life.
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