Comment Log Display

California Air Resources Board
1001 "I" Street
P.O. Box 2815
Sacramento, CA 95812


Re:  Premature deaths from fine airborne particulate matter

Dear Board Members:

I am writing to you concerning the October 24, 2008 staff report
entitled "Methodology for Estimating Premature Deaths Associated
with Long-term Exposure to Fine Airborne Particulate Matter in
California", which was subsequently cited in the November, 2008
report by Hall, Brajer, and Lurmann entitled "The Benefits of
Meting Federal Clean Air Standards in the South Coast and San
Joaquin Valley Air Basins".  My principal concerns are these:

1.  In neither document is the term "premature death" defined.  In
the section on public comments and staff responses (Appendix 5) of
the staff report, BNSF Railway expressed that same concern (Point #
19).  I found the staff response to be unsatisfactory.  Expected
based upon what?  Air pollution only a contributing factor and not
a cause of death?  Then why emphasize it?  Hall et al. claim a
reduction of 3860 such deaths in SC and SJ for age 30+ and 13 for
infants if the proposed standards are met. That degree of precision
is unwarranted.

2.  No "de minimus" value of PM 2.5 was ever provided.  (BNSF also
asked about that in Point #19.)  I think there should have been. 
Our air will never be perfectly pure.

3.  In parts of the report relative risks were reported as
increases of 10% and 3%, rather than the conventional values of
1.10 and 1.03 that are used in epidemiology.  And I take exception
to the response to Point # 26 raised by JDD: "It is interesting to
note that no epidemiological organization has agreed to this
standard of evidence [a RR of 2.0 or higher]."  See the attachment
to this letter. RRs of 1.1 and 1.03 are very much of a size that an
unmeasured confounder could be the cause of the RR.

4.  In the Executive Summary the authors referred to "uncertainty
intervals".  Do they mean confidence intervals?  (Confidence
intervals are not appropriate, since there was no random sampling. 
I taught statistics for 42 years and still serve as a statistical
consultant.)  Or are those intervals solely connected with the
various sensitivity analyses that were employed?  The “uncertainty
intervals”, whatever they are, should reflect the fact that
multiple factors are under consideration and the bounds specified
in the report are almost certainly too narrow.

5.  As suggested by several of the peer reviewers, the ÄÕ impact
equation for estimating numbers of premature deaths should have
been more carefully explained, especially how the value of â and
its bounds are estimated.  

The purpose for my writing to you now is my understanding that on
December 11th of this year a decision might be made to require
diesel-powered vehicles to meet standards for air pollution that
would cost the trucking industry billions of dollars.   I recommend
that the December 11th decision be deferred until a later time,
since there are so many technical problems that remain to be
resolved.

Respectfully submitted,

Thomas R. Knapp (Prof. Emer., University of Rochester and The Ohio
State University)

Att: