Supporting data for \"Direct observation of changing NOx lifetime in North American cities\"

NOx lifetime can be directly observed from space, and has a nonlinear relationship with its own concentration. At high NOx concentrations, NOx lifetime decreases with decreasing concentration, but at intermediate concentrations, the reverse is true. Here we show that urban NOx lifetime in North America has changed between 2005 and 2014. The shape of these changes is qualitatively consistent with a steady-state model of NOx lifetime with decreasing NOx emissions. The pattern of change suggests that NOx-limited chemistry now controls urban NOx lifetime.氮氧化物（NOx）寿命可通过太空观测直接获取，且与其自身浓度呈非线性相关关系。在高氮氧化物浓度下，氮氧化物寿命随浓度降低而缩短；但在中等浓度区间，情况则恰好相反。本文证实，2005年至2014年间，北美城市区域的氮氧化物寿命发生了变化。该变化的整体趋势在定性上与氮氧化物排放降低情景下的氮氧化物寿命稳态模型相符。这种变化模式表明，当前城市区域的氮氧化物寿命由氮氧化物限制型化学反应主导。