Solar photons in the high-energy ultraviolet (UV) region are responsible for the photolysis of gas molecules leading to the production of highly reactive atoms and radicals, which are the main drivers of oxidation chemistry in the atmosphere. Hydroxyl radicals (OH), which react rapidly and indiscriminately with most atmospheric trace compounds and determine the lifetimes of many atmospheric constituents, are generated in the troposphere primarily via ozone photolysis in a narrow wavelength band between 290 and 320 nm. 1,2 Nitrous acid (HONO) photolysis is an important source of OH in the early morning and late evening, when photons at wavelengths shorter than ~320 nm are attenuated by the atmosphere. 1 Photolysis reactions of reactive chlorine gas species such as hypochlorous acid (HOCl), nitryl chloride (ClNO 2 ), and molecular chlorine (Cl 2 ) can be important sources of chlorine atoms (Cl), which rapidly oxidize volatile organic compounds. 3 Considerable effort has been expended to study photochemistry in the ambient atmosphere. Conversely, the role of photochemistry in indoor air has received little attention, 4 despite the fact that people spend more than 85% of their time

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