Photochemistry indoors has recently been recognized as an important factor affecting indoor air quality. A number of studies have shown that gas phase photochemical reactions can affect the oxidative capacity of the indoor environment by forming radicals: Gomez Alvarez et al. reported elevated hydroxyl radical (OH) levels in a sunlit classroom from nitrous acid (HONO) photolysis indoors, 1 and Lakey et al. reported enhanced OH radicals during bleach cleaning that can be largely explained by a cascade of reactions initiated via molecular chlorine (Cl 2 ) photolysis. 2 Gas-phase oxidant precursors such as formaldehyde (HCHO) and hydrogen peroxide (H 2 O 2 )have also been predicted to photolyze under illumination by indoor sunlight and electric lighting to form OH radicals, 1,3-10 whereas nitryl chloride (ClNO 2 ) and hypochlorous acid (HOCl) released during the use of sodium hypochlorite bleach-based cleaners can be photolyzed by indoor light leading to the production of Cl atoms that react efficiently with most volatile organic compounds (VOCs). 5,11,12