Lydia Wegman/RTP/USEPA/US 

12/20/2007 06:03 PM

	

To

hking@omb.eop.gov, mschwab@omb.eop.gov, rjohansson@omb.eop.gov

cc

richmond.harvey@epa.gov, martin.karen@epa.gov, Tricia
Crabtree/RTP/USEPA/US@EPA, wegman.lydia@epa.gov

Subject

Response to 2 issues from teleconference with OMB on ozone NAAQS









Hi folks,

Please find Harvey and John's response to two questions you raised in
our last discussion about the ozone risk and exposure assessments. 

----- Forwarded by Lydia Wegman/RTP/USEPA/US on 12/20/2007 06:01 PM
-----

Harvey Richmond/RTP/USEPA/US 

12/20/2007 05:52 PM

	

To

Lydia Wegman/RTP/USEPA/US@EPA

cc

Rosalina Rodriguez/RTP/USEPA/US@EPA, Karen Martin/RTP/USEPA/US@EPA, John
Langstaff/RTP/USEPA/US@EPA, Dave Mckee/RTP/USEPA/US@EPA

Subject

Re: response to 2 issues from teleconference with OMB on ozone NAAQS









Lydia,

Below are responses to 2 issues/questions raised by OMB.  These can be
forwarded to OMB.

1.  Is there anything that the APEX exposure modeling output can tell us
about the relationship between the distribution of ambient
concentrations measured at the monitors and the distribution of personal
ozone exposures?

Response: The exposure modeling performed (APEX) for ozone looked at
population distributions of exposure for each urban area and did not
provide information that can address the question raised about the
ratios of ambient concentrations to personal exposures for individuals
or populations living around each monitor in the urban area.

2.  Can you explain the difference between the ratio of 1.33 given in
the Rochester workgroup report relating 8-hr ozone and 24-hr ozone and
the ratio of about 2 given in the OAQPS Staff Paper?

Response:  The ratio discussed on p.35 of the Rochester report relates
to converting the average of 24-hr averages across all monitors in an
urban area to the average of 8-hr averages across all monitors in an
urban area.  In contrast, the ratio of about 2 discussed in the OAQPS
Staff Paper is relating the average of the 24-hr averages across all
monitors in an urban area with the 8-hr average at the highest monitor
within that same urban area.   Clearly, these are two very different
comparisons which are being done for different purposes.

Harvey

    Harvey M. Richmond

    Ambient Standards Group

    Health and Environmental Impacts Division

    U.S. EPA

    C504-06

    RTP, NC  27711

    (office) 919-541-5271

    (fax) 919-541-0237

    (email)  richmond.harvey@epa.gov

