Measurements of jet aircraft emissions at cruise altitude I: The odd‐nitrogen gases NO, NO 2 , HNO 2 and HNO 3

Using a novel aircraft‐borne automatic mass spectrometer, the odd‐nitrogen gases NO, NO 2 , HNO 2 and HNO 3 were for the first time measured in a young exhaust‐trail of a jetliner at cruise‐altitude. The measurements, which took place at an altitude of 9.5 km and a distance of about 2 km from a DC‐9 jetliner, revealed NO and NO 2 to be present with abundances as large as 780 and 150 ppbv, respectively. The acids HNO 2 and HNO 3 reached abundances of 0.52 and 0.46 ppbV, which implies that only about 0.05% of the emitted reactive nitrogen experienced rapid conversion to the stable odd nitrogen reservoir nitric acid. Hence, most of the emitted odd‐nitrogen remained in the reactive form NO and NO 2 , which affect ozone. Nitrous acid (HNO 2 ) turns out to be an excellent tracer for young jet‐aircraft plumes since it is short‐lived and reaches only a very low atmospheric background abundance. The low HNO 3 ‐emission implies that HNO 3 ‐H 2 O nucleation and condensation in jet‐aircraft plumes is hardly favoured by the additional HNO 3 . However, it may still occur due to H 2 O emissions.