Index (x_zamdh) and reference concentration (r_zadh) at index measurement station m and LZ z in observation period II with active LEZ (a = 1) and in observation period I with inactive LEZ (a = 0): matched quadruplets consisting of two index measurement values and two reference measurement values.

<p>The time difference between compared measurement values at day d of the year in period 2 and d+1 of the year in period 1, always with starting time h, is not a full year but 364 days to keep the weekday constant.