11846 Phys. Chem. Chem. Phys., 2011, 13, 11846–11857 This journal is c the Owner Societies 2011 Cite this: Phys. Chem. Chem. Phys., 2011, 13, 11846–11857 Internal structure, hygroscopic and reactive properties of mixed sodium methanesulfonate-sodium chloride particles Y. Liu,w a B. Minofar,z b Y. Desyaterik,y a E. Dames, c Z. Zhu, a J. P. Cain, c R. J. Hopkins,z d M. K. Gilles, d H. Wang, c P. Jungwirth e and A. Laskin* a Received 20th February 2011, Accepted 19th April 2011 DOI: 10.1039/c1cp20444k Internal structures, hygroscopic properties and heterogeneous reactivity of mixed CH 3 SO 3 Na/ NaCl particles were investigated using a combination of computer modeling and experimental approaches. Surfactant properties of CH 3 SO 3  ions and their surface accumulation in wet, deliquesced particles were assessed using molecular dynamics (MD) simulations and surface tension measurements. Internal structures of dry CH 3 SO 3 Na/NaCl particles were investigated using scanning electron microscopy (SEM) assisted with X-ray microanalysis mapping, and time- of-flight secondary ion mass spectrometry (TOF-SIMS). The combination of these techniques shows that dry CH 3 SO 3 Na/NaCl particles are composed of a NaCl core surrounded by a CH 3 SO 3 Na shell. Hygroscopic growth, deliquescence and efflorescence phase transitions of mixed CH 3 SO 3 Na/NaCl particles were determined and compared to those of pure NaCl particles. These results indicate that particles undergo a two step deliquescence transition: first at B69% relative humidity (RH) the CH 3 SO 3 Na shell takes up water, and then at B75% RH the NaCl core deliquesces. Reactive uptake coefficients for the particle–HNO 3 heterogeneous reaction were determined at different CH 3 SO 3 Na/NaCl mixing ratios and RH. The net reaction probability decreased notably with increasing CH 3 SO 3 Na and at lower RH. Introduction Over the last few decades, the fundamental kinetics and mechanisms of heterogeneous reactions on atmospheric particles have been of interest due to their impact on the atmospheric environment and climate change. Sea salt aerosol, generated by wave action and bubble bursting at the ocean surface, have the second largest global burden by mass. 1 Airborne sea salt particles undergo heterogeneous reactions with trace atmospheric species, including OH, HNO 3 ,O 3 , NO 2 ,N 2 O 5 and ClONO 2 . In some of these reactions, photo- chemically inert halides present in sea salt can be converted to reactive halogen species X  and XO  (X = Cl and Br). These halogen species can impact the ozone budget and oxidative capacity of the atmosphere. 2 A noticeable halide deficit in sea salt aerosols is reported in a number of field studies at various geographic locations. 3–9 In regions where sea salt particles are impacted by anthropogenic pollutants, the reaction of gas-phase nitric acid with sodium chloride NaCl(s,aq) + HNO 3 (g) - NaNO 3 (aq) + HCl(g) (R1) is regarded as a major contributor to halide depletion and nitrate enrichment. 10–24 Reaction 1 is also a net sink of atmospheric nitric acid, and hence regulates the gas-particle partitioning of HNO 3 and consequently impacts the atmospheric and aquatic environments. 2,25 Similarly, sea salt particles also react with biogenic sulfur- containing acids through corresponding aqueous chemistry in deliquesced particles. Dimethyl sulfide (CH 3 SCH 3 , DMS) produced by marine phytoplankton is the largest source of a William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P. O. Box 999, MSIN K8-88, Richland, WA 99352, USA. E-mail: Alexander.Laskin@pnl.gov; Fax: (509) 376-6139; Tel: (509) 371-6129 b Institute of Systems Biology and Ecology of the Academy of Sciences of the Czech Republic and Institute of Physical Biology, University of South Bohemia Zamek 136, Nove Hrady, Czech Republic c Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453, USA d Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA e Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, and Center for Complex Molecular systems sand Biomolecules, Flemingovo nam. 2, Prague 6, CZ-16610, Czech Republic w Present address: Department of Chemistry, University of Colorado, Denver, CO 80217, USA. z Present address: Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka city, 6-10-1,812-8581, Japan. y Present address: Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA. z Present address: Detection Department, The Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire, SP4 0JQ, U.K. PCCP Dynamic Article Links www.rsc.org/pccp PAPER Published on 13 May 2011. Downloaded by Princeton University on 07/01/2015 18:11:31. View Article Online / Journal Homepage / Table of Contents for this issue