POWER July 2016 - 28

ENVIRONMENTAL ISSUES
Table 1. Summary of PM measurement options. Source: TRC Companies Inc.
Options
Pros
Quarterly stack monitoring
No initial capital expense for
PM monitor and installation. No
maintenance costs.
Cons
Can only see a snapshot of emissions
once per quarter. It can be
challenging to schedule emission
testing firm during busy seasons.
Do not know results until a week
after the testing is complete.
PM CEMS: full continuous
emissions monitoring system
calibrated by a correlation
curve (PS-11)
Continuous data and can be used
over full calibration range, so
operating limit is the MATS PM
allowable.
Correlation testing (calibrating
monitor) can be difficult on highly
controlled sources. Have to conduct
tests over three distinct emission
levels. Correlation testing can be
expensive, especially if PM spiking
is necessary.
PM CPMS: continuous parameter
monitoring system
Continuous data and the correlation
testing (setting the source-specific
operating limit) is comparatively
easy.
These monitors, based on a range of analytical
detection technologies, can qualify and
quantify target compounds, and when quality
assurance and maintenance procedures
for the systems are defined, they can provide
defensible emissions data.
Gaseous monitors are the most common
CEMS, but recent technological advances
The source-specific operation limit
will always be set below the MATS
PM limit, so the source will not
have as much flexibility in emission
variation before corrective actions
must be taken.
have expanded the availability of PM monitors
beyond those used to measure opacity.
Importantly, modern PM monitors can express
PM emissions as a concentration, thus
allowing comparison to a PM emissions
limit.
Here's a condensed timeline of PM monitoring
development:
■ 1950s and 1960s: The Germans pioneered
and began studying PM detection
technologies.
■ 1970s: PM technologies came to the U.S.
in the form of opacity monitors. Opacity
was considered a surrogate for PM and
Performance Specification 1 (also known
as PS1) was promulgated in 1975.
■ 1996: The Hazardous Waste Combustion
MACT rule was the first to require the use
of PM monitors. The need for a performance
specification to validate PM monitor
data was proposed (PS-11).
■ 1999: The Portland Cement MACT standard
mandated PM monitors, but not until
PS-11 was promulgated (2004).
■ 2012: MATS was promulgated, allowing
certain PM CEMS detection technologies
for filterable particulate matter
(FPM) compliance demonstrations. The
PM monitors could be used as a true PM
CEMS or PM CPMS.
PM monitoring technologies include: light
scattering, beta attenuation (the two most
commonly deployed technologies), probe
electrification, optical scintillation, and light
extinction. From these measurement technologies
and the diligent work of instrument
vendors, today PM monitors can detect and
indicate changes in the amount of FPM in
exhaust gases and are accurate and durable
enough to be utilized as CEMS.
Unlike traditional gaseous monitors, PM
monitors cannot be calibrated like a CEMS
that measures gaseous pollutants. Instead of
using calibration gases, the monitor output
signal must be correlated to a physical PM
measurement that is obtained using an EPA
reference method stack test for PM.
In general, the PM detection principle is a
function of the size, shape, color, concentration,
and material of the PM and is therefore
source specific. Accordingly, PM monitors
must be evaluated for each source over a
range of operating conditions. Furthermore,
PM monitors are different from traditional
gaseous monitors.
It's important to note that MATS allows
choices in how the PM monitor can be used.
When the regulation was first enacted, power
companies had to quickly choose a compliance
strategy. Among the choices were
the use of a PM monitor as a full CEMS or
the use of a PM monitor as a CPMS. Now,
with the experience gained through various
approaches, the time is right to revisit compliance
demonstration strategies using continuous
PM monitors as CEMS or CPMS.
Three Options
Table 1 details the three options for power
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