Direct sulfuric acid formation from the gas-phase oxidation of reduced-sulfur compounds.

Sulfuric acid represents a fundamental precursor for new nanometre-sized atmospheric aerosol particles. These particles, after subsequent growth, may influence Earth´s radiative forcing directly, or indirectly through affecting the microphysical and radiative properties of clouds. Currently considered formation routes yielding sulfuric acid in the atmosphere are the gas-phase oxidation of SO 2 initiated by OH radicals and by Criegee intermediates, the latter being of little relevance. Here we report the observation of immediate sulfuric acid production from the OH reaction of emitted organic reduced-sulfur compounds, which was speculated about in the literature for decades. Key intermediates are the methylsulfonyl radical, CH 3 SO 2 , and, even more interestingly, its corresponding peroxy compound, CH 3 SO 2 OO. Results of modelling for pristine marine conditions show that oxidation of reduced-sulfur compounds could be responsible for up to ∼50% of formed gas-phase sulfuric acid in these areas. Our findings provide a more complete understanding of the atmospheric reduced-sulfur oxidation.