"Johansson, Robert" <Robert_C._Johansson@omb.eop.gov> 

06/14/2007 05:32 PM

	

To

Lydia Wegman/RTP/USEPA/US@EPA

cc

Subject

another comment









Hi Lydia,

 

Last interagency review comment for page 147:

 

(4)  With respect to the uncertainties about estimated policy-relevant
background concentrations, as discussed in the Staff Paper (section
5.4.3), alternative assumptions about background levels had a variable
impact depending on the health effect considered and the location and
standard analyzed in terms of the absolute magnitude of the risk
estimates.  There was relatively little impact on either absolute or
relative changes in lung function risk estimates due to alternative
assumptions about background levels.  With respect to O3-related
non-accidental mortality, alternative assumptions about background
levels had a greater impact.  Estimates of risk remaining upon just
meeting the current or alternative standards were most affected, with
differences of +/-50 percent or larger observed in many of the areas. 
For example, the Staff Paper notes that “estimates assuming higher PRB
levels results in decreased estimates of non-accidental mortality
incidence per 100,000 that are 50% or greater less than the base case
estimates” (Staff Paper, pg. 5-82).  Alternative assumptions about
background levels had a greater impact on the nonaccidental mortality
risk estimates associated with more stringent 8-hour standards.  Notable
differences were observed for nonaccidental mortality in some areas,
particularly for more stringent standards. The overall pattern of
reductions, expressed in terms of percentage reduction relative to the
current standard, was significantly less impacted by alternative
assumptions for background than the absolute magnitude of the risks. 
Potential uncertainties with regard to policy-relevant background levels
may include: (1) stratospheric contributions to tropospheric ozone
levels which consist of long-lived (1 to 2 months) stratospheric ozone
which is well mixed with tropospheric ozone and diffuses downward over
time; (2) potential trends in stratospheric ozone levels due to changes
in stratospheric circulation or to reduction of ozone depleting
chemicals; (3) ozone levels due to lightning strikes in PRB
calculations; and (4) potential uncertainty with regard to PRB ozone
levels having to do with increases in ozone precursors elsewhere in the
world.  EPA asks for comments on these issues and on how they may relate
to PRB levels and to possible health effects.

 

Thanks,

Rob

 

________________________________________________

Robert Johansson, Ph.D.

OMB/OIRA/NREA

725 17th St. NW, Room 10202

Washington, DC 20503

(P) 202-395-7873

(F) 202-395-7285

(E) RJohansson@omb.eop.gov

 

