With the exception of emissions by aircraft, the NO_x produced by these activities is emitted into the boundary layer. Most of the NO_x produced is ultimately converted to HNO₃ and rained out of the atmosphere. However, thunderstorms, as well as making their own NO_x contribution from lightning, can transport NO_x from the boundary layer well into the troposphere.

The degree of NO_x transfer from the boundary layer to the free troposphere is difficult to evaluate and model.

Aircraft inject NO_x produced by high temperature combustion into the upper troposphere and lower stratosphere. Although the amount of NO_x generated by aircraft is small compared to that generated at the ground by other anthropogenic activities, it is probably important because it is injected at a sensitive altitude where only a small fraction of the ground-level NO_x is uplifted by convective storms. The significance of aircraft emissions of NO_x for the troposphere may therefore be greater than its low absolute value might suggest.

Because the lifetime of NO_x is short at the surface and much longer in the upper troposphere the altitude of the emission determines the lifetime of the NO_x.

In the boundary layer about 60% of NO_x is in the form of NO₂. At higher altitudes, however, the proportion of NO to NO₂ increases.