Field observations and quantum chemical calculations have shown that organic amine compounds may be important for new particle formation involving H<sub>2</sub>SO<sub>4</sub>. Here, we report laboratory observations that investigate the effect of trimethylamine (TMA) on H<sub>2</sub>SO<sub>4</sub>-H<sub>2</sub>O nucleation made under aerosol precursor concentrations typically found in the lower troposphere ([H<sub>2</sub>SO<sub>4</sub>] of 10<sup>6</sup>−10<sup>7</sup> cm<sup>−3</sup>; [TMA] of 180–1350 pptv). The threshold [H<sub>2</sub>SO<sub>4</sub>] needed to produce the unity <i>J</i> was from 10<sup>6</sup>−10<sup>7</sup> cm<sup>−3</sup> and the slopes of Log <i>J</i> vs. Log [H<sub>2</sub>SO<sub>4</sub>] and Log <i>J</i> vs. Log [TMA] were 4–6 and 1, respectively, strikingly similar to the case of ammonia (NH<sub>3</sub> ternary nucleation (Benson et al., 2011). At lower RH, however, enhancement in <i>J</i> due to TMA was up to an order of magnitude greater than that due to NH<sub>3</sub>. These findings imply that both amines and NH<sub>3</sub> are important nucleation species, but under dry atmospheric conditions, amines may have stronger effects on H<sub>2</sub>SO<sub>4</sub> nucleation than NH<sub>3</sub>. 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.