Heterogeneous reactions of gaseous methanesulfonic acid with NaCl and sea salt particles

Methanesulfonic acid (MSA) has been identified as one of the most important intermediate products of DMS reactions in the atmosphere. Although considerable amounts of MSA have been found in the marine boundary layer, little is known about the interaction of gaseous MSA with sea salt particles. To understand the fate of MSA in the atmosphere and its potential importance in atmospheric chemistry, the heterogeneous reactions of gaseous MSA with micron-scale NaCl and sea salt particles were studied using diffuse reflectance infrared Fourier transform spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The CH₃SO₃Na and CH₃SO₃ ⁻ were the major products of the condensed phase of the reaction of gaseous MSA with NaCl and with sea salt particles. The steady-state uptake coefficient was determined to be (5.94±2.32)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with NaCl particles and (2.23±1.25)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with sea salt particles. The heterogeneous reaction of MSA with NaCl particles was found to be first-order for MSA. The reaction mechanisms were discussed. Supported by the National Natural Science Foundation of China (Grant No. 40490265) and the National Basic Research Priorities Program (Grant No. 2002CB410802)