Evaporation of sulphate aerosols at low relative humidity
Georgios Tsagkogeorgas1, Pontus Roldin2,3, Jonathan Duplissy2,4, Linda Rondo5, Jasmin Tröstl6, Jay G. Slowik6, Sebastian Ehrhart5,a, Alessandro Franchin2, Andreas Kürten5, Antonio Amorim7, Federico Bianchi2, Jasper Kirkby5,8, Tuukka Petäjä2, Urs Baltensperger6, Michael Boy2, Joachim Curtius5, Richard C. Flagan9, Markku Kulmala2,4, Neil M. Donahue10, and Frank Stratmann11Leibniz Institute for Tropospheric Research, 04318, Leipzig, Germany 2Department of Physics, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland 3Division of Nuclear Physics, Lund University, P.O. Box 118, 221 00, Lund, Sweden 4Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland 5Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438, Frankfurt am Main, Germany 6Paul Scherrer Institute, 5232, Villigen, Switzerland 7Fac. Ciencias & CENTRA, Universidade de Lisboa, Campo Grande, 1749 – 016, Lisboa, Portugal 8CERN, 1211, Geneva, Switzerland 9California Institute of Technology, Pasadena, CA 91125, USA 10Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA anow at: Atmospheric Chemistry Department, Max Planck Institute for Chemistry, 55128, Mainz, Germany
Received: 23 Nov 2016 – Accepted for review: 12 Dec 2016 – Discussion started: 16 Dec 2016
Abstract. Here we explore the vapour pressure of sulphuric acid at very low relative humidity, where evaporation of sulphuric acid from particles can be important in the atmospheres of Earth and Venus. We performed experiments in the CLOUD chamber at CERN forming sulphuric acid particles via nucleation and then measuring evaporation versus temperature and relative humidity. We modelled the experiments with the ADCHAM model to constrain the thermodynamic properties governing the evaporation of sulphuric acid. ADCHAM includes a thermodynamics module coupled to an aerosol dynamics module. We derived the mole fractions and activity coefficients of H2SO4, HSO4−, SO42− and SO3 in the particles and then simulated the condensation and evaporation of H2SO4 and SO3. We constrained the equilibrium constants for the dissociation of H2SO4 to HSO4− (KH2SO4) and the dehydration of H2SO4 to SO3 (xKSO3). Our results suggest that particle shrinkage is mainly governed by H2SO4 evaporation, however, we cannot dismiss a contribution from SO3 evaporation. We conclude that KH2SO4 = 2–4 ∙ 109 mol ∙ kg−1 at 288.8 ± 5 K and xKSO3 ≥ 1.4 ∙ 1010.
Tsagkogeorgas, G., Roldin, P., Duplissy, J., Rondo, L., Tröstl, J., Slowik, J. G., Ehrhart, S., Franchin, A., Kürten, A., Amorim, A., Bianchi, F., Kirkby, J., Petäjä, T., Baltensperger, U., Boy, M., Curtius, J., Flagan, R. C., Kulmala, M., Donahue, N. M., and Stratmann, F.: Evaporation of sulphate aerosols at low relative humidity, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1045, in review, 2016.