"King, Heidi R." <Heidi_R._King@omb.eop.gov> 

03/12/2008 11:58 AM

	

To

Ron Evans/RTP/USEPA/US@EPA, Lydia Wegman/RTP/USEPA/US@EPA, Harvey
Richmond/RTP/USEPA/US@EPA

cc

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

Subject

edit for preamble









Harvey - suggested edit related to our conversation on FN 15 / 2001 air
qual or meteorological data, using language from Staff Paper:

 

[1][1] PRB O3 concentrations used in the O3 risk assessment were defined
in chapter 2 of the Staff Paper (EPA, 2007, pp. 2-48, 2-54) as the O3
concentrations that would be observed in the U.S. in the absence of
anthropogenic emissions of precursors (e.g., VOC, NOx, and CO) in the
U.S., Canada, and Mexico.  Based on runs of the GEOS-CHEM model (a
global tropospheric O3 model) applied for the 2001 warm season (i.e.,
April to September) monthly background daily diurnal profiles for each
of the 12 urban areas for each month of the O3 season were simulated
using meteorology for the year 2001.  Based on these runs from the
GEOS-CHEM model, the Criteria Document states that current estimates of
PRB background O3 concentrations are generally in the range of 0.015 to
0.035 ppm in the afternoon, and they are generally lower under
conditions conducive to high O3 episodes. They are highest during spring
and decline into summer. Higher values tend to occur at higher
elevations during spring due to contributions from hemispheric pollution
and stratospheric intrusions. The CD states that the GEOS-CHEM model
applied for the 2001 warm season report PRB O3 values for afternoon
surface air over the United States that are likely 10 ppbv too high in
the southeast in summer, and accurate within 5 ppbv in other regions and
seasons.

