Major gas phase products of the photooxidation of methyl sulfide (CH3SCH3) under atmospheric conditions are sulfur dioxide, formaldehyde, ozone and nitric acid, along with smaller amounts of methyl nitrate. Substantial formation of light-scattering aerosols was observed, with inorganic sulfate and methane sulfonic acid as major components of the aerosol. Experimental results are discussed in terms of reaction pathways initiated by reaction of methyl sulfide with the hydroxyl radical.