The effect of trimethylamine on atmospheric nucleation involving H₂SO₄

Abstract. Field observations and quantum chemical calculations have shown that organic amine compounds may be important 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 10⁶−10⁷ cm⁻³; [TMA] of 180–1350 pptv). The threshold [H₂SO₄] needed to produce the unity J was from 10⁶−10⁷ 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 ammonia (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 findings imply that both amines and NH₃ are important nucleation 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 troposphere.