Extended Data Fig. 4: Comparison of growth rates and chemical composition in four simulations at +5 °C and −10 °C with the thermodynamic model MABNAG.
From: Rapid growth of new atmospheric particles by nitric acid and ammonia condensation
The simulation points are shown in Fig. 3a (filed diamonds, with activation; open diamonds, without activation). a, c, e, g, Temporal evolution of the particle diameter. b, d, f, h, Temporal evolution of the particle-phase chemical composition. The left-hand column (a, b, e, f) shows simulations without activation. The right-hand column (c, d, g, h) shows simulations with activation. We set the HNO3 mixing ratios at 80 pptv and 400 pptv with 1,500 pptv NH3 at +5 °C, and set the HNO3 mixing ratios at 20 pptv and 0.5 pptv with 1,500 pptv NH3 at −10 °C, to simulate unsaturated (a, b, e, f) and supersaturated (c, d, g, h) conditions, respectively. All other conditions were held constant for the simulations, with the [H2SO4] at 2 × 107 cm−3 and relative humidity at 60%. Activation corresponds to a rapid increase in the nitric acid (nitrate) mass fraction; the simulations for activation conditions suggest that water activity may be an interesting variable influencing activation behaviour. The activated model results (c, d, g, h) confirm that supersaturated nitric acid and ammonia lead to rapid growth of nanoparticles. The simulated activation diameter at +5 °C is roughly 4 nm, similar to that from the chamber experiment (4.7 nm, Fig. 3a); at −10 °C the simulated activation diameter is less than 2 nm, smaller than observed.
