NO2: Quadruplets of continuous NO2-measurements: index stations (Ind), reference stations (Ref) before (pre) and after (post) introduction of LEZ.

Ind.diff and Ref.diff denote differences between index measurements and between reference measurements (negative post-pre differences indicate lower values after introduction of LEZ). Concentrations measured in µg/m3.N: number of quadruplets; Min: minimum, p5: 5th percentile, p50: median, mean: arithmetic average, p95: 95th percentile, max: maximum, unit:

Ind.diff与Ref.diff分别表示指标测量值间的差值与参考测量值间的差值（后减前差值为负值时，表明引入低排放区（Low Emission Zone, LEZ）后对应指标的数值更低）。测量浓度的单位为微克每立方米（µg/m³）。统计指标说明如下：N为四元组数量；Min为最小值，p5为5%分位数，p50为中位数，mean为算术平均值，p95为95%分位数，max为最大值，单位：