Photochemistry is a largely unconsidered potential source of reactive species such as hydroxyl and peroxy radicals (OH and HO, "HO") indoors. We present measured wavelength-resolved photon fluxes and distance dependences of indoor light sources including halogen, incandescent, and compact fluorescent lights (CFL) commonly used in residential buildings; fluorescent tubes common in industrial and commercial settings; and sunlight entering buildings through windows. We use these measurements to predict indoor HO production rates from the photolysis of nitrous acid (HONO), hydrogen peroxide (HO), ozone (O), formaldehyde (HCHO), and acetaldehyde (CHCHO). Our results suggest that while most lamps can photolyze these molecules, only sunlight and fluorescent tubes will be important to room-averaged indoor HO levels due to the strong distance dependence of the fluxes from compact bulbs. Under ambient conditions, we predict that sunlight and fluorescent lights will photolyze HONO to form OH at rates of 10-10 molecules cm s, and that fluorescent lights will photolyze HCHO to form HO at rates of ∼10 molecules cm s; rates could be 2 orders of magnitude higher under high precursor concentrations. Ozone and HO will not be important photochemical OH sources under most conditions, and CHCHO will generally increase HO production rates only slightly. We also calculated photolysis rate constants for nitrogen dioxide (NO) and nitrate radicals (NO) in the presence of the different light sources. Photolysis is not likely an important fate for NO indoors, but NO photolysis could be an important source of indoor O.

Indoor oxidizing capacity in occupied residences is poorly understood. We made simultaneous continuous time-resolved measurements of ozone (O), nitric oxide (NO), nitrogen dioxide (NO), and nitrous acid (HONO) for two months in an occupied detached home with gas appliances in Syracuse, NY. Indoor NO and HONO mixing ratios were higher than those outdoors, whereas O was much lower (sub-ppbv) indoors. Cooking led to peak NO, NO, and HONO levels 20-100 times greater than background levels; HONO mixing ratios of up to 50 ppbv were measured. Our results suggest that many reported NO levels may have a large positive bias due to HONO interference. Nitrous acid, NO, and NO were removed from indoor air more rapidly than CO, indicative of reactive removal processes or surface uptake. We measured spectral irradiance from sunlight entering the residence through glass doors; hydroxyl radical (OH) production rates of (0.8-10) × 10 molecules cm s were calculated in sunlit areas due to HONO photolysis, in some cases exceeding rates expected from ozone-alkene reactions. Steady-state nitrate radical (NO) mixing ratios indoors were predicted to be lower than 1.65 × 10 molecules cm. This work will help constrain the temporal nature of oxidant concentrations in occupied residences and will improve indoor chemistry models.

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

Urban grime can be an important substrate for heterogeneous reactions in cities. Studies performed using laboratory-prepared urban grime proxies and urban grime collected from the field indicate that the physicochemical properties of urban grime can greatly affect heterogeneous reaction rate constants. We investigated several properties of urban grime collected from two cities in the north-east region of the United States of America. Optical and Raman microscopy indicated that urban grime collected from these regions consists primarily of particles as opposed to a uniform film. Total carbon analysis and ion chromatography were used to determine the bulk composition of the urban grime from both cities. Comparing these results to reported compositions of urban grime from cities in Canada and Europe showed strong similarities between different locations, with some variations for specific ions, such as higher chloride levels in North American cities and higher sulfate levels in some European cities. Absorbance spectra demonstrated that urban grime can absorb sunlight across the ultraviolet region. It may therefore be able to participate in photochemical reactions (either hindering them via processes such as the inner filter effect or enhancing them via processes such as photosensitization).

Solutes can greatly affect pollutant photodegradation kinetics in atmospheric aqueous phases such as surface waters, atmospheric aerosols, and cloud and fog droplets. We have measured photooxidation rate constants of the polycyclic aromatic hydrocarbons (PAHs) pyrene and anthracene in aqueous solutions containing environmentally relevant concentrations of halide salts (NaCl, NaBr, and NaI) and in seawater. Chloride, bromide, and iodide did not affect pyrene photodegradation kinetics but increased anthracene photodegradation rate constants at low halide concentrations. The largest anthracene rate constant measured, in the presence of 0.2 M NaCl, was 3.4 times larger than that in deionized water. Smaller enhancements were observed in the presence of NaBr and NaI, with maximum rate constants observed at concentrations of 1 × 10 −5 and 1 × 10 −8 M, respectively. We determined that this enhancement was due to singlet oxygen ( 1 O 2 ) generation resulting from interactions between halides and electronically excited anthracene. Interactions between pyrene and halides also formed 1 O 2 , but this did not affect pyrene's observed photodegradation rate constant. At higher halide concentrations, anthracene photodegradation rate constants showed a weak negative dependence on halide concentration, likely due to quenching of anthracene's excited triplet state. Our results suggest that the fates of some PAHs in saline environments could differ from those predicted by kinetics measured in deionized water in the absence of solutes.