Indoor Photochemical Radical Production: Wavelength-Resolved Photon Fluxes and Rate Calculations

Date of Award

May 2018

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Tara F. Kahan


Air Quality, Artificial Light Sources, Indoor, Photochemistry, Photon Flux, Radicals

Subject Categories

Physical Sciences and Mathematics


Photochemical reactions indoors have largely been ignored due to an assumed lack of high energy photons. We have measured wavelength-resolved photon fluxes of several indoor light sources (various standard consumer lightbulbs, fluorescent tubes, and sunlight). Light was detected in the actinic region (wavelengths < 400 nm) for the majority of these sources. Measured photon fluxes were used to calculate production rates of hydroxyl (OH) and peroxy (HO2) radicals (collectively referred to as HOx) from the photolysis of trace compounds found indoors. Our results indicate that most light sources indoors can initiate photolysis of compounds indoors. However, under ambient conditions, only the photolysis of nitrous acid (HONO) by sunlight and the photolysis of formaldehyde (HCHO) by fluorescent tubes will contribute significantly to HOx concentrations indoors.

We extended our calculations of indoor radical production rates to evaluate a potentially unforeseen risk with hospital decontamination processes. More advanced cleaning techniques, developed for the elimination of harmful pathogens, utilize photolabile compounds. Some of the chemicals can photolyze to form HOx or chlorine radicals (Cl). We determined that radical concentrations may be orders of magnitude higher than background levels after the use of these cleaning processes. This could lead to lowered air quality within the room where disinfection occurred and cause adverse health effects for occupants.

The few photon flux measurements performed indoors have been done under a limited range of conditions. We present the first photon fluxes from inside a residence and two consumer vehicles, along with measurements in an academic building. We evaluated the influence of several factors on indoor photon fluxes from sunlight. We predicted OH production rates from HONO photolysis indoors under different illumination conditions to assess the importance of photochemistry on indoor air composition. OH production rates are likely to be relatively high under a number of conditions indoors.


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