ARB Research Seminar

This page updated October 10, 2013

In-duct air cleaning devices: ozone emission rates and test methodology

Photo of Glenn Morrison, Ph.D.

Glenn Morrison, Ph.D., Missouri University of Science and Technology

November 08, 2013
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


The Air Resources Board's (ARB) air cleaner regulation limits ozone emissions from portable air cleaning devices, but in-duct devices were exempted due to the lack of test data and a test method. Dr. Morrison will share the results of a collaborative study, which examined emission rates from electrically connected in-duct devices and resulting indoor concentrations of ozone in buildings. In their study, a detailed standard test method was developed in parallel with the construction and development of a laboratory test apparatus. Eleven electrically connected in-duct air cleaners (seven models) were tested on the laboratory test apparatus using the newly developed test method. Ozone emission rates in laboratory tests ranged from undetectable, to greater than 350 mg/hr. With some exceptions, emission rates were generally not sensitive to flow or temperature.

Field tests of electrically connected devices were completed in seven residential buildings (1 in Tulsa, OK, 6 in the Davis/Sacramento area of California). One commercial unit was tested in a classroom. The incremental increase in the ozone concentration due to the operation of these devices ranged from undetectable to greater than 150 ppb, with devices operating normally. Similarly, estimated emission rates in field sites ranged from undetectable to greater than 400 mg/hr. Two intentional ozone generators increased the ozone concentration in field residences by greater than 50 ppb. For a typical house, the mass-balance model predicts that an emission rate of approximately 150 mg/hr would raise the indoor concentration by about 50 ppb. A dynamic (time-dependent) multi-zone model found that separate rooms can have very different and elevated, indoor air concentrations even when the air handler is off, but the device is operating. Based on model analysis, laboratory testing and field studies, the project team concluded that the use of electrically connected in-duct air cleaners of the types studied in this research can increase residential indoor concentrations of ozone above the current California limit set for other ozone generating devices.

Speaker Biography

Glenn Morrison, PhD., is a Professor of environmental engineering at the Missouri University of Science and Technology. Dr. Morrison has worked for 25 years on environmental chemistry and environmental engineering problems, focusing primarily on the indoor environment. In laboratory and field research, he has extensively studied the chemistry of ozone with indoor and human surfaces and the impact that chemistry has on occupant exposure to ozone and chemical reaction products. Professor Morrison is an NSF CAREER awardee, a Fellow of the Academy of the International Society of Indoor Air Quality and Climate (ISIAQ), current Vice President (and President as of July 2014) of ISIAQ.

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