Comment Log Display

The California Air Resources Board (ARB) has proposed to regulate
ozone emitting air cleaners. The effect of this regulation is to
reduce consumer exposure to ozone, a criteria pollutant recognized
to be associated with morbidity and mortality. The regulation has
the further benefit of reducing exposure to the byproducts of
ozone reactions with surfaces and some gas-phase compounds. I
support the California Air Resource Board’s efforts to reduce
Californian’s exposure to ozone and its byproducts.

Ozone is a very reactive compound that oxidizes compounds present
in the air and on indoor surfaces, releasing a wide variety of
chemicals. Commercial efforts to chemically improve indoor air
with ozone have been misguided at best, dangerous at their worst.
The fact that ozone can react rapidly to remove a small number of
organic compounds have led manufacturers of ozone generating “air
cleaners” to claim that their products effectively destroy organic
pollutants . The reaction rates with most indoor odors are far too
small to effect any significant change in exposure. For those
compounds that are “destroyed”, such as the “terpenes” used to as
scents, the chemical products of these reactions appear to be
worse than the original scent. Ozone also reacts with surfaces
with adverse outcomes. In early work, Weschler et al. (1992)
showed that adding ozone to a chamber with carpet actually
INCREASES the total mass concentration of inhalable compounds.
Ozone has been consistently shown to increase indoor
concentrations of aldehydes, ketones and carboxylic acids due to
reactions with materials that would be present in almost any
indoor environment. Most of these materials are themselves benign
and “natural”, including natural terpenes used as scent and 
triglycerides derived from vegetable oils. 

In the attached file, I briefly review the chemistry of ozone in
indoor environments. The growing literature on this subject shows
us that a substantial fraction of ozone injected into indoor
environments will raise indoor levels of reaction products that
are troubling. 

Given the clear benefits of reducing ozone exposure, and the
suspected and known hazards associated with ozone reaction
products, every effort should be made to reduce and eliminate
ozone emissions from consumer devices. The ARB regulation is a
step in the right direction. However, I echo the sentiments
expressed by Richard Corsi of the University of Texas, Austin: I
hope that the Air Resources Board reviews their proposed 50 ppb
limit and considers a lower value in the near future.