Gas-phase H2SO4 was measured with an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF, Aerodyne Research Inc. and TOFWERK AG) 27 equipped with a chemical ionization (CI) inlet (CI-APi-TOF) 28 employing nitrate reagent ions. All methodological details and calculations concerning the instrumental setup are already described in Rose et al. (2021) .