The effect of trimethylamine on atmospheric nucleation involving

Field observations and quantum chemical calcula- tions have shown that organic amine compounds may be im- portant for new particle formation involving H2SO4. Here, we report laboratory observations that investigate the effect of trimethylamine (TMA) on H2SO4-H2O nucleation made under aerosol precursor concentrations typically found in the lower troposphere ((H2SO4) of 10 6 10 7 cm 3 ; (TMA) of 180-1350 pptv). The threshold (H2SO4) needed to produce the unity J was from 10 6 10 7 cm 3 and the slopes of Log J vs. Log (H2SO4) and Log J vs. Log (TMA) were 4-6 and 1, respectively, strikingly similar to the case of ammo- nia (NH3) ternary nucleation (Benson et al., 2011). At lower RH, however, enhancement in J due to TMA was up to an order of magnitude greater than that due to NH3. These find- ings imply that both amines and NH3 are important nucle- ation species, but under dry atmospheric conditions, amines may have stronger effects on H2SO4 nucleation than NH3. Aerosol models should therefore take into account inorganic and organic base compounds together to fully understand the widespread new particle formation events in the lower tropo- sphere.