1Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland
2Finnish Meteorological Institute, P.O. Box 1627, 70211 Kuopio, Finland
3Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
4School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
5School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
Received: 10 Jun 2013 – Discussion started: 13 Sep 2013
Abstract. The effect of inorganic semivolatile aerosol compounds on the cloud condensation nucleus (CCN) activity of aerosol particles was studied by using a computational model for a DMT-CCN counter, a cloud parcel model for condensation kinetics and experiments to quantify the modelled results. Concentrations of water vapour and semivolatiles as well as aerosol trajectories in the CCN column were calculated by a computational fluid dynamics model. These trajectories and vapour concentrations were then used as an input for the cloud parcel model to simulate mass transfer kinetics of water and semivolatiles between aerosol particles and the gas phase.
Revised: 12 Mar 2014 – Accepted: 01 Apr 2014 – Published: 20 May 2014
Two different questions were studied: (1) how big a fraction of semivolatiles is evaporated from particles after entering but before particle activation in the DMT-CCN counter? (2) How much can the CCN activity be increased due to condensation of semivolatiles prior to the maximum water supersaturation in the case of high semivolatile concentration in the gas phase?
Both experimental and modelling results show that the evaporation of ammonia and nitric acid from ammonium nitrate particles causes a 10 to 15 nm decrease to the critical particle size in supersaturations between 0.1% and 0.7%. On the other hand, the modelling results also show that condensation of nitric acid or similar vapour can increase the CCN activity of nonvolatile aerosol particles, but a very high gas phase concentration (as compared to typical ambient conditions) would be needed. Overall, it is more likely that the CCN activity of semivolatile aerosol is underestimated than overestimated in the measurements conducted in ambient conditions.
Romakkaniemi, S., Jaatinen, A., Laaksonen, A., Nenes, A., and Raatikainen, T.: Ammonium nitrate evaporation and nitric acid condensation in DMT CCN counters, Atmos. Meas. Tech., 7, 1377-1384, doi:10.5194/amt-7-1377-2014, 2014.