Uptake of methanol vapor in sulfuric acid solutions

The uptake of gas-phase methanol by liquid sulfuric acid has been investiga ted over the composition range of 40-85 wt % H2SO4 and the temperature rang e of 210-235 K. Laboratory studies were performed with a flow-tube reactor coupled to an electron-impact ionization mass spectrometer to detect trace gases. While reversible uptake was the primary mechanism at low acid concen trations, an irreversible reaction between methanol and sulfuric acid at lo w temperatures, forming methyl hydrogen sulfate and dimethyl sulfate, was o bserved at all concentrations. At compositions >65 wt % H2SO4, more than 90 % of uptake was found to be reactive. On the basis of the uptake data and t he calculated liquid-phase diffusion coefficients, the product of the effec tive Henry's law constant (H*) and the square root of the overall liquid-ph ase reaction rate (k(1)) was calculated as a function of acid concentration and temperature. The results suggest that the reaction with sulfuric acid forming methyl hydrogen sulfate and dimethyl sulfate is the dominant loss m echanism of methanol and that the oxidation of methanol is only a minor sou rce of hydroxyl radicals in the upper troposphere.