POWER November 2012 - 57

AIR QUALITY
Hazy Timetable for EPA's Proposed
Tighter PM2.5 Standards
On June 15, in response to a court order, the U.S. Environmental Protection Agency
(EPA) proposed new lower limits on particulate matter (PM) emissions that
are scheduled for release in mid-December. Even with implementation delays,
now is a good time to start paying closer attention to the requirements
of the proposed standard.
By Angela Neville, JD
P
articulate matter (PM) is a complex
mixture of extremely small particles and
liquid droplets. PM comprises a number
of components, including acids (such as nitrates
and sulfates), organic chemicals, metals,
and soil or dust particles. The size of particles
is directly linked to their potential for causing
health problems. The U.S. Environmental
Protection Agency (EPA) is concerned about
particles that are 10 micrometers in diameter
or smaller (PM10) because those are the ones
that generally pass through the throat and nose
and enter the lungs. Once inhaled, these particles
can affect the heart and lungs and cause
serious health effects (Figure 1).
Particles may be emitted directly or formed
in the atmosphere by transformations of gaseous
emissions such as sulfur oxides (SOx),
nitrogen oxides (NOx), and volatile organic
compounds (VOCs). Examples of secondary
particle formation include the following:
■ The conversion of sulfur dioxide (SO2
) to
sulfuric acid droplets that further react with
gaseous ammonia to form various sulfate
particles such as ammonium sulfate.
■ Reactions involving gaseous VOC yielding
organic compounds with low ambient
temperature (saturation) vapor pressures
1. Particulate policy. Particulates of different
diameters have different effects on the
human body and often originate from different
sources. PM10 and PM2.5 particles are easily
inhaled and penetrate airways and lungs.
Source: California Environmental Protection
Agency Air Resources Board
Hair cross section (60 mm)
that condense on existing particles to form
secondary organic aerosol particles.
The EPA groups particle pollution into
two categories:
■ Inhalable coarse particles, such as those
found in industries handling dusty materials
like coal, are larger than 2.5 micrometers
and smaller than 10 micrometers in diameter.
These particles are classified as PM10.
■ Fine particles (PM2.5), such as those found
in smoke and haze, are 2.5 micrometers in
diameter and smaller. These particles can
be directly emitted from sources such as
forest fires, or they can form when gases
emitted from power plants react in the air.
Due to environmental concerns, coal-fired
power plants are required to operate a particulate
collection system to control the release
of particulate emissions. These systems
include inertial collectors (cyclone collectors),
fabric filter collectors (baghouses), wet
scrubbers, and electrostatic precipitators.
POWER has published a variety of articles
about PM standards and PM control technologies.
The most recent examples (available in
the archives at www.powermag.com) include
" Particulate Matter Air Quality Standards
Continue to Evolve " (June 2011) and " EPRI
Bridges Industry R&D Gaps " (January 2012).
Regulating Particulates in the Past
The first rules regulating PM were promulgated
in 1971 under the Clean Air Act (CAA).
Since that time, the EPA has continually updated
the PM standards (Table 1) to better
2. The air is getting cleaner. This graph illustrates the reduction in the amount of the
six common pollutants (SO2, NOx, PM, CO, ozone, and lead) in relation to other key economic
indicators over the past two decades. Source: EPA
220%
200%
180%
160%
140%
120%
100%
80%
60%
40%
20%
0%
-20%
-40%
-60%
-80%
Human hair
(60 mm diameter)
November 2012 | POWER
PM10
(10 mm)
PM2.5
(2.5 mm)
95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11
Year
www.powermag.com
57
Gross domestic product
Vehicle miles traveled
Population
Energy Consumption
CO2 emissions
Aggregate emissions
(Six common pollutants)

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POWER November 2012

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