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 10(8)-10(9) cm(-3) range and [NH3] from 10-50 ppbv (similar to 2 x 10(11)-1 x 10(12) cm(-3)), the enhancement factor (EF) compared to the binary system ranges up to similar 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. Citation: Benson, D. R., M. E. Erupe, and S.-H. Lee (2009), Laboratory-measured H2SO4-H2O-NH3 ternary homogeneous nucleation rates: Initial observations, Geophys. Res. Lett., 36, L15818, doi: 10.1029/2009GL038728.