Abstract
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.
Highlights
New particle formation (NPF) is a global phenomenon (Kulmala et al, 2004) that can impact the nature and amount of clouds through formation of cloud condensation nuclei (CCN) in the atmosphere (Merikanto, 2009)
Since the particle measurements with CPC have size dependent detection efficiencies and the formed particles grow by condensation in addition to nucleation, the observed slope of Log J vs. Log [H2SO4] included both nucleation and condensation effects and condensation growth made the slope appear higher than the actual values
We provide the first comprehensive laboratory investigation of multicomponent aerosol nucleation involving TMA, as a function of aerosol precursor concentrations
Summary
New particle formation (NPF) is a global phenomenon (Kulmala et al, 2004) that can impact the nature and amount of clouds through formation of cloud condensation nuclei (CCN) in the atmosphere (Merikanto, 2009). While there are thousands of organic compounds in the atmosphere, amines have become increasingly important, since recent quantum chemical calculations have shown that they can form neutral and ion clusters with H2SO4 molecules more efficiently than NH3 (Kurten et al, 2008), even though amine concentrations are lower than that of NH3. This is further supported by a recent experiment which shows that amines can substitute ammonium to aminium in sub-3 nm ammonium sulfate clusters (Bzdek et al, 2010). More evidence on the possible role of amines in NPF was found in field measurements which showed the presence of aminium ions in nanoparticles (Makela et al, 2001; Smith et al, 2004, 2008)
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