Analysis of Chemical and Physical Effects of Ultraviolet Bulbs on Cooking Emissions

Abstract

There is a growing recognition of the risks to health, fire hazard, and air quality from cooking emissions. Recent research has identified what is emitted when foods are cooked. Some of the emitted mass is captured in the exhaust system. The balance is expelled into the atmosphere. The outlet of the exhaust system is a demarcation point—upstream the captured mass is the operator or building owner's concern, whereas downstream into the atmosphere, it affects air quality. Building codes have long required operators to deal with the upstream section. More recently, regulations are being placed on what kitchens can emit to the atmosphere. The industry is responding to this challenge with product innovations. Recently gained understanding of cooking emissions supports much of the innovation—but not all. This paper evaluates the purported benefit of adding better filtration and ultraviolet C (UVC) bulbs in kitchen hoods. A “UV hood” claims a two-step process to reduce emissions: better filters capture more emitted mass, and UVC photons and ozone drive photo-decomposition and oxidation reactions of some of the remaining greasy constituents. Adding UV to a hood at least doubles the cost compared to an equivalent non-UV hood. There is evidence that UV hoods do reduce some emissions. The essential question is whether improved performance is due to UV or relatively inexpensive, improved filters. Experimentation exposed an oleic acid aerosol, representative of cooking emissions, to UVC energy and ozone at higher concentrations and for longer exposure times than can occur in a UV hood. Particle-size and chemical changes were measured on samples collected with UV bulbs off and on. Results strongly indicate little change is happening and most emission reductions are caused by better filtration and not UV. The conclusion is that UV hoods fall short of claimed performance, and unreacted ozone may increase air pollution. IMPLICATIONS Commercial cooking emissions present problems in certain locations because of odors, fine particles, and volatile organic compounds (VOCs). Air quality regulations are increasingly requiring emission reductions. One attempted innovation is to place improved filters and ultraviolet bulbs in kitchen hoods. UV and the accompanying ozone are claimed to photo-decompose and oxidize much of the emitted organic constituents to smaller components. Testing with a representative emission constituent demonstrates that UV has little effect in reducing the mass or composition of the emissions, and that relatively inexpensive, better filters are responsible for most reduction. Additionally, air pollution, due to created ozone, may be increased. © 2011 Air and Waste Management Association.