Chemical processes in sea-salt chloride depletion observed at a Canadian rural coastal site Xiaohong Yao a , Leiming Zhang b, * a Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China b Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada article info Article history: Received 22 July 2011 Received in revised form 19 September 2011 Accepted 30 September 2011 Keywords: Chlorine chemistry Inorganic ions Nitrogen species Size-resolved aerosols abstract Chloride depletion in sea-salt aerosols was studied using size-segregated inorganic ions data collected at a Canadian rural coastal site during a summer (June 29eJuly 15, 2002) and a fall campaign (October 25 e November 15, 2002). Three samples collected in the fall campaign had high concentrations of sea-salt and ammoniated sulfate and nitrate aerosols and were used to study the relative importance of different chemical reactions contributing to the depletion. The percentage depletion (Cl  depletion (%)) increased substantially with decreasing particle size (up to 86% for particles in the size range of 1.0e3.1 mm). For particles >6.2 mm, the observed NO 3  was responsible for all the depleted Cl  ; but less than a quarter of the depletion was explained by the HCl-released reaction between NaCl and HNO 3 ; the rest of the depletion was likely due to the non-HCl-released reactions, e.g., between NaCl and N 2 O 5 . For particles in the size range of 3.1e6.2 mm, the NO 3  was responsible for nearly 80e90% of all the depleted Cl  via HCl-released and/or non-HCl-released reactions; the remaining depletion was likely due to the reactions releasing Cl 2 , HOCl, etc. Particles >3.1 mm were mostly neutral acidity while a portion of particles at 1.0e3.1 mm was acidic. SO 4 2 was only responsible for Cl  depletion (%) in acidic particles at 1.0e3.1 mm and the highest Cl  depletion (%) was observed in acidic particles of this size range. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. 1. Introduction Oceans cover approximately two-thirds of the earth’s surface and their emitted sea-salt aerosols play important roles in local, regional and global environmental and climate problems (Lewis and Schwartz, 2004; Simon et al., 2009, 2010; Finlayson-Pitts, 2010; Hara et al., 2010). In the polluted coastal and marine atmo- sphere, fresh sea-salt aerosols age rapidly through various physical and chemical processes such as heterogeneous reactions and cloud and fog processing (Zhuang et al., 1999; Yao et al., 2003; Lewis and Schwartz, 2004; Zhao and Gao, 2008; Kikuchi et al., 2009). In the last several decades, much attention has been paid to atmospheric chlorine chemistry associated with heterogeneous chemical reac- tions on sea-salt aerosols. It has been reported that heterogeneous reactions can release gaseous reactive chlorine compounds, including HCl, Cl 2 , ClNO 2 , HOCl, etc., from sea-salt aerosols (Finley and Saltzman, 2006; Osthoff et al., 2008; Keene et al., 2009; Kercher et al., 2009; Lawler et al., 2009). However, specific and sensitive methods used to measure these gaseous reactive chlorine compounds are not well established, limiting our understanding of these processes occurring in the atmosphere. The same can be said to the potential impact of these compounds on air pollution and climate change. Alternatively, analytical methods on particulate chloride, other inorganic ions and gases such as HNO 3 , NO x , NO y and SO 2 have been well established (Kerminen et al., 1998; Zhuang et al., 1999; Yao et al., 2003; Zhao and Gao, 2008; Keene et al., 2009; Zhang et al., 2010). A comprehensive analysis of these particulate ions, partic- ularly in different-sized aged sea-salt aerosol particles, together with HNO 3 , NO x , NO y and SO 2 gases would shed some light into the processes releasing gaseous reactive chlorine compounds. In this study, a suite of measurements made at a Canadian rural coastal site, including size-segregated inorganic ions and related ambient gases are used to explore possible chemical reactions and their relative contributions to the chloride depletion in different-sized sea-salt aerosol particles. 2. Methodology The percentage of chloride depleted in aged sea-salt aerosols is conventionally defined as: * Corresponding author. E-mail address: leiming.zhang@ec.gc.ca (L. Zhang). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.09.081 Atmospheric Environment 46 (2012) 189e194