Infrared Studies of the Reaction of Methanesulfonic Acid with Trimethylamine on Surfaces

Abstract

Organosulfur compounds generated from a variety of biological as well as anthropogenic sources are oxidized in air to form sulfuric acid and methanesulfonic acid (MSA). Both of these acids formed initially in the gas phase react with ammonia and amines in air to form and grow new particles, which is important for visibility, human health and climate. A competing sink is deposition on surfaces in the boundary layer. However, relatively little is known about reactions after they deposit on surfaces. We report here diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies of the reaction of MSA with trimethylamine (TMA) on a silicon powder at atmospheric pressure in synthetic air and at room temperature, either in the absence or in the presence of water vapor. In both cases, DRIFTS spectra of the product surface species are essentially the same as the transmission spectrum obtained for trimethylaminium methanesulfonate, indicating the formation of the salt on the surface with a lower limit to the reaction probability of γ > 10(-6). To the best of our knowledge, this is the first infrared study to demonstrate this chemistry from the heterogeneous reaction of MSA with an amine on a surface. This heterogeneous chemistry appears to be sufficiently fast that it could impact measurements of gas-phase amines through reactions with surface-adsorbed acids on sampling lines and inlets. It could also represent an additional sink for amines in the boundary layer, especially at night when the gas-phase reactions of amines with OH radical and ozone are minimized.