29. To improve clarity, it would be useful to move the request for
information to the beginning of the document and include the rest as
background.  

Response:  We do not understand this comment and the specific language
it’s referring to.  

30. When will the Santa Monica Study be ready?

Response:  The Santa Monica study conducted by the South Coast Air
Quality Management District is completed and the draft final report is
expected to be ready this Spring.  The Santa Monica study conducted by
EPA was recently finalized and is now available at: 
www/epa.gov/otaq/aviation.htm.

31. We recommend that EPA include the following questions, to help EPA
collect useful information on how regulation of avgas may cause
commercial disruptions:

How many companies manufacture AvGas today?

Do we have to import AvGas to meet current demand?

How is AvGas transported to airports? (either piped into airports or by
truck)

For companies developing alternatives, what is the best estimate as to
when they’d be able to meet current demand?

Where does the research stand on a standard for unleaded fuel for
high-performance engines?

To what extent are U.S. operators of general aviation aircraft concerned
that any changes made to U.S. avgas requirements (such as, for example,
requiring manufacturers to produce engines that consume non-leaded
fuels), could disrupt their ability to fly to/from locations outside the
United States because of a potential lack of those non-leaded fuels?

To what extent are U.S. manufacturers and other sellers of general
aviation aircraft concerned that a change in U.S. avgas requirements
could affect the international competitiveness of their products by, for
example, decreasing the demand for U.S. aircraft overseas if they are
not compatible with avgas used in those non-U.S. markets? 

Response:  In consultation with industry it is understood that any
near-term or long-term unleaded avgas or low lead would provide
equivalent performance to 100LL (i.e, equivalent octane performance);
the fuel would need to meet the ASTM specification for 100LL.  We
currently ask for comment on potential problems with the approach we
outline in this section of the ANPR. We’re willing to add another
sentence requesting comment on avgas issues, but it will be more
generally worded than what is suggested here, in order to be consistent
with the level of detail in our other requests for comment.  We can get
you some suggested text tomorrow.

Page 13 line 12:  It is indicated that 100LL is the most commonly
available type of avgas but it is not clear here if this is the most
commonly used.  Suggest noting this here and not later in the paragraph
as it is presented.

Response:  We will add the note regarding the dominant use of 100LL
where suggested.  

Page 14 line 6:  It is noted that if all avgas was 100LL, it would
account for approximately 34,000 tons of lead emitted to the air.  Would
this be double if 100 octane only were used as indicated by the doubling
of the concentration of lead in 100 octane relative to 100LL?  

Response:  Yes.  

Page 17 line 8:  It is mentioned that EPA has discussed it
“endangerment finding” authority at length in recent notices.  It
should be noted here that these endangerment findings are with respect
to green house gases and not lead.

Response:  We will add that these recent findings refer to greenhouse
gases.  

Page 17 line 18:  Concentrations of the standard are presented in text
unites of micrograms per cubic meter but in previous and future text
units are presented as µg/m3.  We suggest notations be used
consistently throughout the document.

Response:  We have corrected this.

Page 20 line 10:  It is noted that EPA has found that air pollutant
emissions that amount to 1.2 percent of the total inventory met the
statutory test for contribution.  How does this value compare to the
value for lead in avgas? (What percent of Pb in avgas contributes to the
total inventory of Pb?)

Response:  As noted in the ANPR, avgas lead contributes to 50% of the
total inventory for lead in 2005.  For future actions we will be
evaluating, as noted in Section VI.A.2., the contribution of avgas lead
to areas that are designated nonattainment for lead.

Page 29 line 12:  It is noted that particles size influences the amount
of time spent in [insert “the”] aerosol phase.  It should be noted
as well this influences their residence time in the atmosphere.  

Response:  We have made this correction.  The next sentence, beginning
with “In general, larger particles tend to deposit more
quickly,…..” describes particle size as a factor in residence time
in the atmosphere.

Page 30 line 6:  It is noted “Once deposited to surfaces, lead can
subsequently be resuspended into the ambient air and, because of the
persistence of lead, emissions of this metal contribute to environmental
media concentrations for many years into the future”.  It should be
added that the emissions contribute to environmental media
concentrations for many years into the future “as it is cycled within
and between environmental media such as soil, air, and water”.  

Response:  We have added this phrase to the sentence as suggested.

Page 31 line 6:  Insert at the end of the paragraph “as described
above”.

Response:  We have made this addition.

Page 48 top:  Volume of avgas produced presented in gallons yet
concentrations of Pb in avgas are presented in g/L.  We suggest the
gallon notation also be converted to liters here and present the
concentrations in g/L as well as g/gal as noted in the equation in the
next paragraph.

Response:  We will provide this information in a footnote in this
section.  

Page 51 last ¶:  General aviation and air taxi acronyms are presented
here but should be defined in the preceding paragraph where GA and TA
are listed with no definition.

Response:  We have corrected this.  The original acronyms were provided
on page 13 so we removed the definition of GA and AT on page 51.

Page 53 last ¶: What is the concentration of Pb in 100 Octane in units
of g/L so that one may compare to the 0.56 g/L presented for 100LL in
the previous sentence?  

Response:  We have added the information that Pb in 100 Octane is
present at a concentration of 1.12 g/L.

Page 57 line 17: typo: “an” should be “and”

Response:  We have made this correction.

Page 62 last ¶:  Particulate emissions from piston-engine aircraft are
presented as 10,000 µg/m3.  It would be helpful to put this value in
perspective with respect to ambient air TSP air quality standards (i.e.,
for particles less than 2.5 micron in diameter, the 24 hour attainment
standard is 35 µg/m3).

Response:  The particulate matter concentration of 10,000 µg/m3 was
extrapolated from exhaust measurements made in the air immediately
exiting the engine.  These concentrations are not directly comparable to
ambient air quality standards since the emissions have not undergone
dilution and dispersion in the ambient air.  

Page 63 ¶2:  “due to their “small” size”… We suggest an
(i.e., typically less than one micron in diameter).

Response:  We have added this parenthetical information.

Page 71 ¶1:  It is noted “We are requesting comment on the
availability of additional monitoring or modeling studies that evaluate
the air quality impact of lead emissions from piston-engine aircraft as
well as potential impacts on soil, house dust, surface water or other
environmental media”, we suggest adding a request for comment on
studies that will also assess potential impact on public health and
welfare.

Response:  We have added this request for comment on page 71 at the end
of ¶1.

Page 86 top:  There is a discussion of lead concentrations in fish.  In
an effort to put these numbers in perspective, fish advisory levels for
lead in fish should be presented too.

Response:  States establish advisory levels for pollutants measured in
fish.  We are intending to collecting state-specific information
regarding lead advisory levels and we have added a request for this
information on page 86.

Summary of interagency working comments on draft rule under EO 12866.  

These comments do not necessarily represent the views of OMB and are
subject to further policy review.

