POWER November 2015 - 68

COMMENTARY
Reduce Ozone When and
Where It Matters Most
Valerie Thomas
J
Paul Kerl
ust as we were drafting this commentary, the U.S. Environmental
Protection Agency (EPA) issued a new ground-level
ozone rule, tightening the standard from 75 to 70 ppb. The
projected human health and environmental benefits are substantial.
Yet there has been significant concern about tightening the
ozone standards because of compliance cost.
As it happens, our research team at the Georgia Institute of
Technology recently developed a new way to help meet air quality
standards that might reduce the costs of meeting the new
ozone rule. Our method is not an end-of-pipe air pollution control
technology. Rather, we take advantage of the fact that ozone
concentrations vary substantially by day and by hour, depending
on the emissions from local and regional sources as well as on
atmospheric chemistry and atmospheric conditions such as temperature
and mixing. Emissions from a specific hour of the day
can have a disproportionately large-or minimal-impact on the
pollution that forms, owing to the synergy with emissions from
other hours combined with the effects of changing winds, atmospheric
mixing, and sunlight.
What's interesting about this is that for a power plant operating
at full capacity, on some days and at some times the resulting
human health impacts may be low, whereas on other days-even
similar days at the same time-health impacts can be elevated.
Basically, our method, which we call APOM (for Air Pollution
Optimization Model), targets high-impact times, reducing health
impacts at a lower cost. During low-impact time periods, the operations
of power plants do not need to change, minimizing the
impact on electricity generation cost. During high-impact times,
some generation is either shifted to power plants that will have
less effect on ozone concentrations in highly populated regions
at that specific time, or generation is reduced using demand
management. Because this method can be used when its benefits
are greatest, and because it is managed entirely through
power system operations, without purchase of pollution control
equipment, it can reduce ozone levels at lower cost. (See www.
apom.gatech.edu for more details and an animation.)
Why Hasn't This Been Done Before?
Power systems use computer models to control the operations
of their power plants throughout the day, determining the level
at which each power plant should operate as the day progresses.
Our method allows a simplified air quality impact model to
be included as part of a power system's operation model. The
simplified " reduced form " air quality model is based on a very
comprehensive model, called CMAQ, used by the scientific community,
government agencies (including the EPA), and stakeholders
worldwide to simulate and study air pollution formation
and forecast air quality. CMAQ does a great job, but it is too slow
and complex to run the thousands of times needed for APOM.
Using a technique developed by our team called DDM-3D,
we can determine from one CMAQ simulation how air quality
across a region responds to emissions from power plants and
other targeted sources, without repeating CMAQ simulations for
68
each emissions scenario. This leads to a reduced form model that
responds almost exactly like CMAQ to changes in emissions, but
instead of taking days to run, takes less than a second.
New Method Still Under Development
In our first demonstration of this technique, we focused on reducing
health impacts in the state of Georgia by using mathematical
optimization to quickly sift through a huge number of possible
electricity generating patterns. By considering many ways to adjust
power plant operations as the day goes on, balancing ozone
impacts with power plant operation costs on an hourly basis
every day, the APOM method was able to search out and find
low-cost ways to improve air quality and human health.
More needs to be done before this method is ready for broad
operational deployment. Also, although our case study demonstration
was done for an electricity generation system, the same
method could be applied to industrial sources, transportation
sources, and residential sources of ozone-producing emissions.
There are examples of similar approaches that have successfully
been incorporated in the operation of electricity systems. One is
the use of congestion pricing. When the transmission system is
congested, the operator chooses alternative (often more expensive)
generating units to relieve system congestion in a given
region. These prices differ in terms of time and space. Pricing air
quality in the same way is now a possibility with this approach.
Facilitating a Broader Mix of Generation
The key advantage of this approach is that it can find low-cost
ways to improve air quality. A second advantage is that it can
be applied soon, for existing facilities. While pollution control
equipment or replacement of emission sources may be the best
approach, the APOM approach can be applied quickly. It can also
be applied anywhere in the world. In locations with significant
air quality challenges, this approach can provide benefits before
pollution control technology can become widespread. A third
advantage is that the APOM approach can allow different kinds
of emission sources to work together, using market-based approaches,
to reduce ozone levels at least cost.
The heart of the APOM approach is to find the lowest cost ways
to change operations when it matters most-times when ozone
concentrations would be highest. This approach can work with
high-emitting sources and, in fact, could allow high-emitting
sources to continue operating while contributing to meeting the
new air quality standards. Because of this, reliance on the APOM
approach is unlikely to be able to substitute for improved technology
that will reduce emissions permanently and comprehensively.
Yet, it can be an opportunity for electricity generators,
industrial facilities, and other sources to remain in operation and
meet emissions limits at lower costs than they have expected. ■
-Valerie Thomas, Paul Kerl, Juan Moreno Cruz, Athanasios
Nenes, Matthew Realff, Armistead Russell, and Joel Sokol are
at the Georgia Institute of Technology; Wenxiang Zhang now
works at Trinity Consultants.
www.powermag.com
POWER | November 2015
http://apom.gatech.edu http://www.powermag.com
POWER November 2015

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