We're about to get new ozone rules from the Environmental Protection Agency, which would tighten the so-called "8-hour standard" from 84 parts per billion to somewhere in the 70s.

Expect this to cost you, for the following reasons:

Neither of these is particularly disturbing — I mean, we're talking the actual air you breathe, fercryingoutloud — unless you wonder if maybe the research was carefully designed to give the results that the regulators wanted. It might go something like this:

The laboratory studies used by the EPA to justify a tougher standard fail to take into account the substantial difference between ambient concentrations and personal exposure. Federal, state, and local authorities use fixed ambient monitoring stations to measure ozone concentrations but this does not measure the amount of ozone people actually inhale. In other words, the EPA sets policy based upon ambient concentration but then uses laboratory studies based on personal exposure to validate the need for a more stringent ozone standard.

Since ambient monitors do not consider the time that people spend indoors, ambient concentration is 1.67 times to 2.5 times higher than personal exposure. When laboratory studies assess the health effects of a 60ppb to 80ppb personal exposure, the ambient concentration needed to have those effects is actually 100ppb to 134ppb. Thus, the ambient-based standards set by the EPA are automatically stricter than the levels recommended by the studies.

So there's a fudge factor. Nothing particularly unusual about that. But is it just a matter of who defines the scale?

There are no compelling data to warrant a stricter standard. In laboratory tests, only two out of 30 healthy college students experienced a temporary reduction of 10 percent in lung function at a personal exposure of 60ppb. Personal exposure of 51ppb, which most resembles the current standard of 84ppb, had no negative effects on those tested.

These findings suggest that the current standard is actually too stringent. Even the EPA recognizes that "using ambient concentrations to determine exposure generally overestimates true personal O3 exposures by approximately 2- to 4-fold in available studies, resulting in attenuated risk estimates."

And there's one further consideration: ground-level ozone in any given place at any given moment is highly dependent upon the actual weather at that time. It's the interaction of sunlight with volatile organic compounds that produces the stuff; which means that inevitably, we have less control over the matter than we think we do, especially in places like Oklahoma where the weather is, shall we say, capricious. We might be able to make a small dent in the VOCs — this is the whole point of the "ozone alerts" we get in the summertime and would presumably be the focus of future state ozone-compliance efforts — but we can't do a thing about sunlight, unless we ratchet up particulate emissions, which might be worse than ozone.

If, as expected, metropolitan areas in Oklahoma are found to be out of compliance with the new standards, the state will have to have a new ozone-mitigation progam in place within five years.

The Vent

  8 March 2008

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