Atmos. Chem. Phys. Discuss., 10, 22395-22414, 2010
www.atmos-chem-phys-discuss.net/10/22395/2010/
doi:10.5194/acpd-10-22395-2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Ternary homogeneous nucleation of H2SO4, NH3, and H2O under conditions relevant to the lower troposphere
D. Benson, A. Markovich, and S.-H. Lee
Kent State University, Department of Chemistry, Kent, Ohio 44240, USA

Abstract. Ternary homogeneous nucleation (THN) of H2SO4, NH3 and H2O has been used to explain new particle formation in various atmospheric regions, yet laboratory measurements have failed to reproduce atmospheric observations. Here, we report laboratory observations of THN made under conditions relevant to the lower troposphere (H2SO4 of 106–107 cm−3, NH3 of 0.08–20 ppbv, and 288 K). Our observations show that NH3 can enhance atmospheric H2SO4 aerosol nucleation and the enhancement factor (EF) in nucleation rate due to NH3 increases linearly with increasing NH3 and increases exponentially with decreasing H2SO4 and RH. The critical clusters of ternary homogeneous nucleation contain 3–5 molecules of H2SO4, 1–4 molecules of H2O, and only 1 molecule of NH3. The composition of H2SO4 and H2O in critical clusters and the threshold of H2SO4 concentrations required for the unit nucleation rate both do not vary in the presence and absence of NH3. These observations can be directly used to improve aerosol nucleation models to correctly assess how man-made SO2 and NH3 affect aerosol formation and CCN production at the global scale.

Citation: Benson, D., Markovich, A., and Lee, S.-H.: Ternary homogeneous nucleation of H2SO4, NH3, and H2O under conditions relevant to the lower troposphere, Atmos. Chem. Phys. Discuss., 10, 22395-22414, doi:10.5194/acpd-10-22395-2010, 2010.
 
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