POWER June 2012 - 44

AIR QUALITY
PSD Requirement: PM2.5 NAAQS
Compliance Demonstration. For sources
that trigger PSD review for PM2.5, a compliance
demonstration for the PM2.5 NAAQS
is required. NAAQS compliance demonstrations
typically involve the estimation of
ground-level concentrations (GLCs) that
consist of two components:
■ Calculated predictions of GLCs that are
based, in part, on emission factors for the
source being permitted, as well as other
stationary sources in the region, which are
input to computer-based air pollutant dispersion
models, and
■ Measured GLCs or background levels of
the pollutant of interest, which are recorded
by ambient monitors.
These two components-the model predictions
at numerous points (that is, receptors) over
a wide geographic region and the existing background
pollutant level in the region-are added
together and compared against the NAAQS to
assess compliance at each receptor.
One of the key components of a modeling
analysis is the development of an inventory of
emission sources. Sources of PM have historically
modeled only primary or direct PM emissions,
and in recent years, primary emissions
were required to include the condensable PM
component in addition to the filterable PM component
of emissions. Now, consideration also
must be given to secondary formation of PM for
NAAQS compliance demonstrations. The EPA
is expected to issue PM2.5 modeling guidance in
the late spring/early summer of 2012, with which
it will likely provide suggestions for how to account
for both primary and secondary PM2.5.
With regard to secondary PM2.5, this accounting
could be of a qualitative nature,
using a " weight-of-evidence " type of discussion;
however, the potential dilemma for some
larger combustion sources is that they could
be required to conduct a quantitative analysis
involving the use of complex photochemical
modeling, depending on the magnitude of NOx
and/or SO2
emissions.
That EPA guidance also is expected to address
the development of PM2.5 background
concentrations. Typically, background concentrations
are derived from actual monitored ambient
concentrations of the pollutant(s) of interest.
However, in many areas of the country that are
currently in attainment of the PM2.5 NAAQS,
monitoring data show background concentrations
very close to the 24-hour and/or annual
NAAQS; in other words, there isn't much " buffer "
available for modeled sources' GLCs. With
the inclusion of condensable PM in the sources'
primary emissions and the addition of the secondary
contribution of PM2.5, NAAQS compliance
demonstrations could become significantly
more problematic for sources in a location where
only a very small buffer is available. The buffer
will be further reduced should the EPA administrator
further tighten the annual PM2.5 NAAQS
compliance requirements for those sources still
located in attainment areas.
Those applying for a new permit will be
challenged to supply the required information
given the uncertainty of the qualitative versus
quantitative analysis for secondary PM2.5
formation that will be required to demonstrate
compliance with PM2.5 NAAQS, as well as the
required background concentrations of PM2.5.
Affected sources will need to work closely with
their state/local regulators to develop a plan that
conforms with the EPA's new PM2.5 modeling
guidance, along with a potentially more restrictive
NAAQS. This burdensome process is sure
to generate much discussion and debate over the
coming months.
The energy service business
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Closing Thoughts
The permitting of emission sources of PM2.5,
whether located in an attainment area or a nonattainment
area for PM2.5, will continue to be
challenging. The key to permitting a new source
will be an assessment of available emission factors
to determine the representativeness of the
factors based on source operating parameters,
operating modes, and fuel type, especially in
consideration of the documented issues with
EPA RMs. The recent requirement by the EPA
to account for condensable PM emissions makes
it even more imperative that applicants carefully
evaluate representativeness of the emissions data
and, where necessary, propose alternative, more
appropriate emission factors. Nonrepresentative
data can have significant project-altering effects
(with regard to costs and schedules) with regard
to PSD and NNSR applicability analyses, the
number of emission " offsets " that need to be acquired
(for NNSR sources), and NAAQS compliance
demonstrations (for PSD sources).
The combination of the EPA's new modeling
Un l i k e s e r v i c e p r o v i de r s t ha t h a v e e n t e r e d
t he e n e r g y s e r v i c e bu s i n e s s f r om o t h e r
i n d u s t r i e s , T u r boCa r e ha s a l wa y s f o c u s e d
o n t h e un i que need s o f t h e u t i l i t y
an d i n d u s t r i a l t u r boma c h i n e r y o p e r a t o r .
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POWER | June 2012
guidance for PM2.5 and potentially lower 24-hour
PM2.5 NAAQS will further increase the complexity
of NAAQS compliance demonstrations
while simultaneously increasing the uncertainty
of the results of such analyses. The ramification
will surely be to extend the permitting process
period and make it more costly. Therefore, it is
imperative to evaluate projected PM2.5 emissions
and potential permitting challenges early in
the design phase of a project to avoid unexpected
and expensive permit delays. ■
-Louis Corio (lcorio@zephyrenv.com) is
a senior air quality scientist and Robert
Newman, PE, BCEE (rnewman@zephyrenv.com)
is a principal at Zephyr Environmental
Corp., Columbia, Md.
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POWER June 2012

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