Laboratory‐measured H2SO4‐H2O‐NH3 ternary homogeneous nucleation rates: Initial observations

We have measured nucleation rates of sulfuric acid‐water‐ammonia (H2SO4‐H2O‐NH3) ternary homogeneous nucleation (THN), with a fast flow nucleation reactor attached to two chemical ionization mass spectrometers (CIMSs) to measure H2SO4 and NH3 concentrations simultaneously. Under our experimental conditions with a temperature of 288 K and RH from 4–42% and initial [H2SO4] in the 108–109 cm−3 range and [NH3] from 10–50 ppbv (∼2 × 1011–1 × 1012 cm−3), the enhancement factor (EF) compared to the binary system ranges up to ∼1,000 depending on [H2SO4], [NH3] and RH; EF also exponentially increases with decreasing RH and decreasing initial [H2SO4]. The numbers of H2SO4 (9–10) and H2O molecules (6–15) in the critical clusters are reduced in the presence of NH3 [(6–8) and (4–10), respectively]; the number of NH3 molecules in the critical clusters is smaller than 2, under our experimental conditions.