2002-03-06
----- Original Message -----
From: "James Frysinger" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "U.S. Metric Association"
<[EMAIL PROTECTED]>
Sent: Wednesday, 2002-03-06 18:40
Subject: Re: [USMA:18584] Re: Pollution article:Weird fraction
> Believe it or not, that's pretty advanced for the EPA, John! A couple of
> years ago I came across one of their standards (lead dust?) that used
units
> of micrograms per square foot. Arghhh.
That is just as bad as grams per mile for NOX emmissions (or whatever
emmissions they are used for).
>
> You might also be surprised to find out how the EPA defines "2.5
micrometer
> particulate matter" ("PM_2.5" to them). It basically relates to a
> distribution of sizes that are detectable by a certain, specified
collector.
> This is not entirely new in the world of specifications, but it doesn't
mean
> what many people would assume on the face of it. I.e., 2.4 um particles
are
> nearly as "nasty" as are 2.5 um particles.
But, somehow I think 2.5 �m is based on 0.0001 inches. Everytime I see
something in metres that contains the numbers "2" and "5" together, such as
2.5 or 25 or 250, etc., I can't help think there is hidden FFU in them. And
if 2.4 �m particles are just as nasty, then why not set the limit at 2 �m?
At least 2 �m doesn't look like hidden FFU.
John
>
> Jim
>
> On Wednesday, 2002 March 06 1821, kilopascal wrote:
> > 2002-03-06
> >
> > The Environmental Protection Agency set average annual limits at 15
> > micrograms per cubic meter in 1997, when it tightened its standards to
> > include fine particulate matter - pollutants measuring less than 2.5
> > micrometers. That is about 1/28th the width of a human hair.
> >
> >
> >
> > That must mean the author figured the human hair is 70 �m thick.
> >
> > Yes, the need to compare 2.5 �m to the thickness of the human hair is
> > somewhat strange, as most people wouldn't know how thick hair is if
their
> > life depended on it. But, then again, one can see how thick hair is and
to
> > imagine that something can be 28 times smaller is awe inspiring. At
least
> > to the author.
> >
> > Also note the lack of using symbols. Why not write it as 15 �g/m^3?
> >
> > John
> ....
