Chemical processes in sea-salt chloride depletion observed at a Canadian rural coastal site

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 29 July 15, 2002) and a fall campaign (October 25 - 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 (CI(-)depietion(%)) increased substantially with decreasing particle size (up to 86% for particles in the size range of 1.0-3.1 mu m). For particles >6.2 mu m, the observed NO3- 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 HNO3; the rest of the depletion was likely due to the non-HCl-released reactions, e.g., between NaCl and N2O5. For particles in the size range of 3.1-6.2 mu m, the NO3- was responsible for nearly 80-90% 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 mu m were mostly neutral acidity while a portion of particles at 1.0-3.1 mu m was acidic. SO42- was only responsible for Cl(-)depletion(%) in acidic particles at 1.0-3.1 mu m and the highest Cl(-)depietion(%) was observed in acidic particles of this size range. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.