Extended Data Fig. 3: Example new particle formation experiment at −50 °C with added HIO_x.

Evolution of vapour concentrations (a), particle-nucleation rates at 1.7 nm, J_1.7 (b), and naturally charged particle number size distribution (dN/dlogD_p) and growth rate measured between 3.2 and 8.0 nm, GR_3.2-8 (nm h⁻¹) (c). The black line in panel c depicts the linear fit of 50% appearance time of particles between 3.2 and 8.0 nm. The expected nucleation rates for HIO_x at the kinetic limit are less than 2 × 10⁻⁴ cm⁻³ s⁻¹. The results show that HIO_x enhances IP_0N nucleation in a similar way as H₂SO₄. Discontinuous lines show missing data. The experimental conditions are: isoprene = 0.07–0.16 ppbv (2.1–4.9 × 10⁹ cm⁻³), O₃ = 95 ppbv (3 × 10¹² cm⁻³), I₂ = 0.4–6.7 × 10⁷ cm⁻³, OH = 3.2 × 10⁶ cm⁻³, HO₂ = 7.4 × 10⁷ cm⁻³, RH = 63% and temperature = −49 °C.