Extended Data Fig. 3: A typical measurement sequence.
From: Rapid growth of new atmospheric particles by nitric acid and ammonia condensation
Nucleation was carried out purely from nitric acid and ammonia, with no sulfuric acid (measured to less than 5 × 104 cm−3 or 2 × 10−3 pptv), as a function of coordinated universal time (UTC), at 60% relative humidity and −25 °C. a, Gas-phase ammonia and nitric acid mixing ratios. The run started with injection of the nitric acid and ammonia flow into the chamber to reach chosen steady-state values near 30 pptv and 1,500 pptv, respectively. The nitric acid flow was increased at 5:53 on 14 November 2018 to prove consistency. b, Clearing-field voltage and ion concentrations. Primary ions were formed from galactic cosmic rays (GCR). The clearing-field high voltage (HV) was used to sweep out small ions at the beginning of the run, and turned off at 05:21 on 14 November 2018 to allow the ion concentration to build up to a steady state between GCR production and wall deposition. c, Particle concentrations at two cut-off sizes (1.7 nm and 2.5 nm). Particles formed slowly in the chamber under ‘neutral’ conditions with the HV clearing field on and thus without ions present. The presence of ions (‘GCR’ condition) caused a sharp increase in the particle-number concentration by about one order of magnitude, with a slower approach to steady state because of the longer wall-deposition time constant for the larger particles. Particle numbers rose again with rising nitric acid.
