AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Laboratory Observations of Temperature- and Humidity- Dependencies of Nucleation and Growth Rates of Sub-3 nm Particles
Huan Yu, SHANHU LEE, University of Alabama in Huntsville
Abstract Number: 33 Working Group: Aerosol Chemistry
Abstract Temperature and relative humidity (RH) are the most important thermodynamic parameters in aerosol formation, yet laboratory studies of nucleation and growth dependencies on temperature and RH are lacking. Here we report the experimentally observed temperature and RH dependences of sulfuric acid aerosol nucleation and growth of sub-3 nm particles. Based on our laboratory observations, we provide empirical algorithms that show nucleation and growth rates as function of relative acidity (RA) of sulfuric acid, RH and temperature together. Experiments were performed in a flow tube in the temperature range from 248-313 K, RH from 1% - 80%, and RA of sulfuric acid from 6×10-5 - 0.38 (corresponding to 2×107 - 109 cm-3). The impurity levels of base compounds were determined to be ammonia less than 23 pptv, methylamine less than 1.5 pptv and dimethylamine less than 0.52 pptv. Our results show that low temperatures favor nucleation at fixed sulfuric acid concentrations, but impede nucleation when RA is fixed. The nucleation mechanism based on collision-limited condensation of free sulfuric acid fails to predict the observed growth rates in the sub-3 nm size range, as well as its dependence on temperature and RH. This suggests that evaporation, sulfuric acid hydration and possible involvement of other ternary species should be considered for the sub-3 nm particle growth.
Yu, H., L. Dai, V. P. Kanawade, S. N. Tripathi, X. Ge, M. Chen, and S-H. Lee, Temperature and RH dependence of aerosol nucleation and growth rates of sub-3 nm particles, J. Geophys. Res., Doi:10.1029/2016JD025619 (2017).