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.

Methods
This dataset was produced by doi: 10.5281/zenodo.2629580

Briefly, NO2 column densities from the Berkeley High Resolution (BEHR) NO2 product, v3.0B (daily) were aligned according to wind direction and integrated in the across-wind direction to product line densities. These line densities were fit with exponentially modified Gaussian functions, and NOx lifetimes derived from the characteristic distance of the exponential and the average wind speed.