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Ozone-Generating Air Cleaners and Indoor Air Chemistry
Ozone-generating air cleaners are marketed to homeowners as well as business establishments ostensibly to remove odors and other contaminants from indoor air. IEMB has characterized ozone and oxides of nitrogen (NOx) emissions from these devices in full-scale environmental chamber tests and characterized performance in a research test house. To date, findings demonstrate that, for those models tested, ozone generation rates are generally within the ranges stated by the manufacturers and some models have the capacity to generate ozone concentrations of 200 parts per billion (ppb) in the test house, well above EPA's 8-hour ambient ozone standard of 80 ppb. Additionally, ozone and nitrogen dioxide emission rates increase with decreasing relative humidity, and the relationship between ozone emission rate and NOx generation rate varies between different models of different manufacturers. Ozone-generating air cleaners equipped with an ozone sensor/controller designed to prevent activation of the ozone generator at concentrations above 50 ppb performed erratically in full-scale chamber tests but appeared to perform as designed in limited short-term (24 h) tests in a research test house. We conclude that more extensive testing is needed to characterize the sensor/controller. However, tests in the research test house clearly demonstrate that these devices are capable of producing ozone concentrations well above those of accepted health guidelines.
IEMB is currently investigating the impact of ozone generators on concentrations of volatile organic compounds (VOCs) in indoor environments. These experiments investigate the chemical reactions that take place when an ozone-generating air cleaner is operated in the presence of emissions from a typical source of VOCs, such as an air freshener or cleaning product. Results demonstrate that the ozone-generating air cleaners have little impact on airborne concentrations of solvents used in consumer products, but do impact concentrations of many of the fragrance compounds emitted by this type of product. Reaction products include formaldehyde and other oxygenated organics. The interaction between ozone and some of the product emissions, such as terpenes, triggers formation of ultrafine particles. IEMB is currently refining analytical approaches to better characterize the "soup" of particles and gases that results from operation of these devices in the presence of VOCs.