NO2: Quadruplets of pooled continuous and diffuse sampler 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.

指标差值（Ind.diff）与参考差值（Ref.diff）分别表示指标测量值之间的差值与参考测量值之间的差值（后测值减前测值的差值为负值时，代表引入低排放区（Low Emission Zone，LEZ）后测量值更低）。浓度测量单位为微克每立方米（µg/m³）。其中，N 代表四元组数量，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。