Fig. 1. Time series of radicals, trace gases and aerosol particles.
Measurements were performed on 23 January 2023 over the Amazon basin north of Manaus (RF 19). a, OH and HO2. b, Isoprene, sum of the first-generation isoprene oxidation products methyl vinyl ketone (MVK), methacrolein (MACR) and isoprene hydroxy hydroperoxide (ISOPOOH) and NO. c, Isoprene-derived organonitrates C5H11O4(ONO2) and C5H10O2(ONO2)2. d, Particle concentrations N2–4 and N4–5, as well as pressure altitude. The light-red bar (T9) indicates the period between 10:05 and 10:10 local time, during which the strongest NPF was detected. Grey bars (T1–T8) represent previous sampling periods of the air mass examined at T9, traced by backward trajectories originating from the position of the aircraft during that period. The ambient temperature was about −58 °C at a flight altitude of 12.3 km during T1–T9. During the 4–5 min of the NPF event encounters, the aircraft travels more than 50 km.