Extended Data Fig. 4: Aerosol formation from pure IP_0N products and mixture of IP_0N, IP_1-2N and H₂SO₄.

Evolution of vapour concentrations (a,b), particle-nucleation rates at 1.7 nm, J_1.7 (c,d), and naturally charged particle number size distribution (dN/dlogD_p) and growth rates measured between 3.2 and 8.0 nm, GR_3.2-8 (nm h⁻¹) (e,f). The black lines in panel f depict the linear fits of 50% appearance time of particles between 3.2 and 8.0 nm. The results show that pure IP_0N aerosol formation is feasible and atmospheric ions can enhance the nucleation rate by a few times. The addition of low concentrations of H₂SO₄ further enhances IP_0-2N nucleation by up to two orders of magnitude. The vertical dashed lines and labels indicate the start of a new stage in which the experimental conditions were adjusted. The dotted black curve in panel d shows the expected H₂SO₄–NH₃ nucleation rate, conservatively assuming that NH₃ is present at the 4 pptv limit of detection^44,93. Stages 1 and 3 are, respectively, under neutral (ion-free) and beam (ion-enhanced) conditions, whereas all of the other stages are under galactic cosmic ray (GCR; natural ion concentrations) conditions. The SO₂ concentration is increased in steps during stages 5–12. The experimental conditions for the right panels are: isoprene = 0.08–0.63 ppbv (2.4–20.0 × 10⁹ cm⁻³), O₃ = 189 ppbv (6 × 10¹² cm⁻³), OH = 2.4 × 10⁶ cm⁻³, HO₂ = 1.8 × 10⁸ cm⁻³, RH = 32% and temperature = −49 °C. The experimental conditions for the left panels are: isoprene = 0.05–0.50 ppbv (1.6–16.0 × 10⁹ cm⁻³), O₃ = 1.2 ppbv (3.8 × 10¹⁰ cm⁻³), SO₂ = 0–1.9 × 10⁸ cm⁻³, OH = 6 × 10⁷ cm⁻³, HO₂ = 1 × 10⁹ cm⁻³, NO = 0.12–0.81 ppbv, NO₂ = 0.57–0.84 ppbv, RH = 52% and temperature = −48 °C.