Overview of low emission zones (LEZs) in German cities included for analysis: 17 LEZs in 6 federal states.

Number of index and reference stations per gaseous component (NO2, NO, NOx) suitable for analysis of the first tier of LEZs until Dec 31, 2009.acontinuous measurements, half-hour concentration averages.bdiffuse samplers, longer sampling periods (over weeks).call data combined (continuous, diffuse), adjusted to concentration averages over 4-weeks periods.dreference station used more than once in comparisons to index stations.