Aircraft exhaust drives formation of ozone and is a dominant anthropogenic influence in the upper troposphere. These impacts are mitigated by non-linear chemistry inside the aircraft plume, which cuts off part of the ozone production pathway and reduces the long-term impact of aircraft in a way which is not captured by current models. The ice clouds which form in aircraft exhaust ("contrails") also play a role, converting emitted nitrogen oxides into more stable forms such as nitric acid.