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

Abstract

We have measured nucleation rates of sulfuric acid‐water‐ammonia (H 2 SO 4 ‐H 2 O‐NH 3 ) ternary homogeneous nucleation (THN), with a fast flow nucleation reactor attached to two chemical ionization mass spectrometers (CIMSs) to measure H 2 SO 4 and NH 3 concentrations simultaneously. Under our experimental conditions with a temperature of 288 K and RH from 4–42% and initial [H 2 SO 4 ] in the 10 8 –10 9 cm −3 range and [NH 3 ] from 10–50 ppbv (∼2 × 10 11 –1 × 10 12 cm −3 ), the enhancement factor ( EF ) compared to the binary system ranges up to ∼1,000 depending on [H 2 SO 4 ], [NH 3 ] and RH; EF also exponentially increases with decreasing RH and decreasing initial [H 2 SO 4 ]. The numbers of H 2 SO 4 (9–10) and H 2 O molecules (6–15) in the critical clusters are reduced in the presence of NH 3 [(6–8) and (4–10), respectively]; the number of NH 3 molecules in the critical clusters is smaller than 2, under our experimental conditions.