The effect of trimethylamine on atmospheric nucleation involving H 2 SO 4

Abstract. Field observations and quantum chemical calculations have shown that organic amine compounds may be important for new particle formation involving H 2 SO 4 . Here, we report laboratory observations that investigate the effect of trimethylamine (TMA) on H 2 SO 4 -H 2 O nucleation made under aerosol precursor concentrations typically found in the lower troposphere ([H 2 SO 4 ] of 10 6 −10 7 cm −3 ; [TMA] of 180–1350 pptv). The threshold [H 2 SO 4 ] needed to produce the unity J was from 10 6 −10 7 cm −3 and the slopes of Log J vs. Log [H 2 SO 4 ] and Log J vs. Log [TMA] were 4–6 and 1, respectively, strikingly similar to the case of ammonia (NH 3 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 NH 3 . These findings imply that both amines and NH 3 are important nucleation species, but under dry atmospheric conditions, amines may have stronger effects on H 2 SO 4 nucleation than NH 3 . 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.