Laboratory-measured H2so4-H2O-NH 3 ternary homogeneous nucleation rates: Initial observations

Abstract

We have measured nucleation rates of sulfuric acidwater-ammonia (H 2SO4-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 [H2SO 4] 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 sim;1,000 depending on [H2SO4], [NH3] and RH; EF also exponentially increases with decreasing RH and decreasing initial [H2SO4]. The numbers Of H 2SO4 (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. Copyright 2009 by the American Geophysical Union.