Julin, Jan and Shiraiwa, Manabu and Miles, Rachael E. H. and Reid, Jonathan P. and Pöschl, Ulrich and Riipinen, Ilona (2013) Mass Accommodation of Water: Bridging the Gap Between Molecular Dynamics Simulations and Kinetic Condensation Models. Journal of Physical Chemistry A, 117 (2). pp. 410-420. ISSN 1089-5639 http://resolver.caltech.edu/CaltechAUTHORS:20130301-161033967
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The condensational growth of submicrometer aerosol particles to climate relevant sizes is sensitive to their ability to accommodate vapor molecules, which is described by the mass accommodation coefficient. However, the underlying processes are not yet fully understood. We have simulated the mass accommodation and evaporation processes of water using molecular dynamics, and the results are compared to the condensation equations derived from the kinetic gas theory to shed light on the compatibility of the two. Molecular dynamics simulations were performed for a planar TIP4P-Ew water surface at four temperatures in the range 268–300 K as well as two droplets, with radii of 1.92 and 4.14 nm at T = 273.15 K. The evaporation flux from molecular dynamics was found to be in good qualitative agreement with that predicted by the simple kinetic condensation equations. Water droplet growth was also modeled with the kinetic multilayer model KM-GAP of Shiraiwa et al. [ Atmos. Chem. Phys. 2012, 12, 2777]. It was found that, due to the fast transport across the interface, the growth of a pure water droplet is controlled by gas phase diffusion. These facts indicate that the simple kinetic treatment is sufficient in describing pure water condensation and evaporation. The droplet size was found to have minimal effect on the value of the mass accommodation coefficient. The mass accommodation coefficient was found to be unity (within 0.004) for all studied surfaces, which is in agreement with previous simulation work. Additionally, the simulated evaporation fluxes imply that the evaporation coefficient is also unity. Comparing the evaporation rates of the mass accommodation and evaporation simulations indicated that the high collision flux, corresponding to high supersaturation, present in typical molecular dynamics mass accommodation simulations can under certain conditions lead to an increase in the evaporation rate. Consequently, in such situations the mass accommodation coefficient can be overestimated, but in the present cases the corrected values were still close to unity with the lowest value at ≈0.99.
|Additional Information:||© 2012 American Chemical Society. Received: October 25, 2012; Revised: December 18, 2012; Published: December 19, 2012. This work was supported by the European Research Council ATMOGAIN (No. 278277). We thank PDC Center for high performance computing for the computational resources. M.S. is supported by the Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowship for Research Abroad. R.E.H.M. acknowledges support from the NERC for a postdoctoral fellowship, and J.P.R. acknowledges the EPSRC for support through a Leadership Fellowship.|
|Official Citation:||Mass Accommodation of Water: Bridging the Gap Between Molecular Dynamics Simulations and Kinetic Condensation Models Jan Julin, Manabu Shiraiwa, Rachael E. H. Miles, Jonathan P. Reid, Ulrich Pöschl, and Ilona Riipinen The Journal of Physical Chemistry A 2013 117 (2), 410-420|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||04 Mar 2013 15:33|
|Last Modified:||04 Mar 2013 15:33|
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