Fresno Bee Newsroom Blog

Exceedances v. violations of air standard

Pop quiz: When the Valley’s air breached the federal ozone standard earlier this month, was it an exceedance or a violation?

In federal air-speak — a legal language invented over the past few decades — it was an exceedance, not a violation

Air quality was a concern during this Cross City Race several years ago.

I called it a violation, which I think is easier to understand when we’re speaking in general terms. I sparingly use the term exceedance when I’m explaining the law or its consequences.

But maybe it’s time to start using both exceedance and violation, and explaining the difference each time for clarity. What do you readers think?

So, let’s talk about difference. You need three exceedances at a monitor to get an official violation. You can see why people who know the difference are upset when I write that the Valley’s two March breaches — now I’ve invented my own air-speak — are violations.

In the legal world, it’s an important distinction. Exceedances are cause for concern. Violations can knock your community out of compliance with the standard. That can lead to penalties and expense for the community involved.

How does a community achieve the federal standard? A federal official emailed me this several years ago:

“A community will meet the eight-hour standard when the three-year average of the annual fourth highest daily maximum eight-hour ozone concentration measured at each monitoring site is less than 76 parts per billion (ppb).”

I’ve just been writing that we need zero violations. I’m pretty sure that would work — for both exceedances and violations.

Honestly, I’ve never been able to write a sentence about the “three-year average of the fourth annual highest daily maximum” and really make it sing.

But I am now seriously thinking of switching from my conversational use of “violations” to the combination of exceedances and violations. Maybe there is value in making the distinction each time I refer to it.

For those who are still awake after reading this, let me know what you think.


8TM says:

For clarity, I suppose you’d better succumb to that ugly bit of bureaucratese. I always notice how the spell check in MS Word doesn’t even recognize exceedance. (Neither does the spellcheck on this posting block.) Even my 1991 fine print OED hadn’t caught on to this bit of jargon, which I’d assumed was lifted from engineering, exceedance flows or exceedance curves, but apparently the on-line OED lists a use of it from 1836. I think breach, rather inspired for everyday parlance, which I hope you’ll continue to use as it has a nicely alarming connotation. That has my vote.

8TM says:

But could you clarify, please, on the ozone standard, this has been vexing me since you posted it: if there are three readings in excess at a site, that is a violation; and yet, one is in compliance, is one not, despite the three excesses when “the three-year average of the annual fourth highest daily maximum eight-hour ozone concentration measured at each monitoring site is less than 76 parts per billion.” Doesn’t this mean, then, the compliance standard makes allowance for three breaches (a violation) at each and every site, since it’s only the fourth highest reading that is averaged? I thought a violation tripped one out of compliance.

David Lighthall says:

Yes Mark, a welcome distinction, thanks. The larger logic behind the distinction is this: EPA recognizes from past experience that vulnerable regions like the SJV are going to experience a certain number of “perfect storm” days when ozone values in this case exceed the daily 8 hr. or 1 hr. standard. In this case, they are allowing us three of those abnormally high days (or hours) and instead counting the 4th highest as being more representative of a typical exceedance day. So can I suggest that you do a second installment that brings the “design value” term into the context of this discussion?

Mark Grossi says:

I’m hoping David Lighthall, the science expert at the San Joaquin Valley Air Pollution Control District, will answer 8TM’s question. I’m interested to hear the answer as well.

As far as “design value,” I will only say that it’s a worthy subject. For now. When it’s 104 outside in a few months, I’ll tackle it. Again, I hope, with the help of David Lighthall.

David Lighthall says:

I took a shot in my previous post explaining the logic of what EPA calls the “form” of the standard, so I will try to build on that. The form of a national air quality standard specifies the particular number of exceedances that constitute a violation. In this case, EPA recognizes that in each ozone season there will be a couple of “outlier” days with very high ozone concentrations due to a “perfect storm” of atmospheric conditions that result in the importation of ozone into the Valley from outside sources that are beyond our contol. These outside sources typically can include (1) the impact of ozone entering the Valley from the SF Bay air basin, (2) elevated ozone from accidental wildfires, (3) ozone transported from ocean vessels in the Pacific, and, (4) last but not least, ozone transported to the Valley from Asia, China in particular.

8TM says:

Thanks, David, but my question is more to the rules of the game: If three exceedances is a violation, then can one simultaneously be in compliance and in violation?

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