United States
              Environmental Protection
              Agency     	
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
              Research and Development
                                               EPA/600/SR-93/088  July 1993
EPA       Project  Summary

               Development of  Sampling  and
               Analytical  Methods  for the
               Measurement of Nitrous  Oxide
               from  Fossil  Fuel Combustion
               Sources
               Jeffrey V. Ryan and Shawn A. Karns
                The combustion of fossil fuels is sus-
               pected to contribute to measured in-
               creases in ambient concentrations of
               nitrous oxide (N2O). Accurate and reli-
               able measurement techniques would
               help to assess the relative contribution
               of fossil fuel combustion N2O emissions
               to the increase in ambient concentra-
               tions. The characterization of NO emis-
               sions from  fossil fuel  combustion
               sources has been hindered by the lack
               of suitable and acceptable grab  sam-
               pling and on-line monitoring method-
               ologies. Grab samples have been
               shown to be compromised by a  sam-
               pling artifact where N2O is actually gen-
               erated in the sample container in the
               presence of SO2, NOx, and moisture.
               On-line monitoring techniques are lim-
               ited and, of those available, instrument
               costs are often prohibitive,  detection
               levels are often insufficient, and the
               techniques are often susceptible to in-
               terferences present in combustion pro-
               cess effluents. The report documents
               the technical approach and results
               achieved while developing a grab sam-
               pling method and an automated, on-
               line gas chromatography method
               suitable to characterize N^O emissions
               from fossil fuel combustion sources.
               The two methods developed have been
               documented  as  EPA/Air and Energy
               Engineering  Research  Laboratory
               (AEERL) Recommended Operating Pro-
               cedures (ROPs).
                   This Project Summary was  devel-
                oped by EPA's Air and Energy Engi-
                neering Research Laboratory, Research
                Triangle Park, NC, to announce key find-
 ings of the research project that is fully
 documented in a separate report of the
 same title (see Project Report ordering
 information at back).

 Introduction
    Nitrous oxide (N2O) has been a great
 concern to  the combustion  community
 largely because the combustion of fossil
 fuels has been proposed as a  potential
 contributor to measured increases in ambi-
 ent N20 concentrations. Currently,  atmo-
 spheric N2O concentrations are increasing
 at nearly 1 ppbv annually from a present
 level of approximately 303 ppbv. This in-
 crease is significant because N2O is con-
 sidered  a  "greenhouse" gas and  is
 associated with stratospheric ozone deple-
 tion. Studies  tracking atmospheric in-
 creases of carbon dioxide (CO2)  over time
 reveal that the increases of both N2O and
 CO2 occur similarly and that increases of
 both these anthropogenic pollutants corre-
 late well with increases in industrial activ-
 ity.
     Early efforts to characterize N2O emis-
  sions from fossil fuel combustion sources
  focused on identifying a relationship be-
  tween nitrogen oxides (NOX) and N2O emis-
  sions. Data were nominally collected in a
  "piggy back"  manner,  where N20 grab
  samples were collected during NOX perfor-
  mance tests. Considerable data exist on
  N2O emissions from diverse combustion
  sources  and techniques firing on various
  fossil fuels. Much of the data reported on
  N2O measurements from fossil fuel com-
  bustion sources were obtained using grab
  sampling methods conducive to a sam-
  pling artifact that biases the measured val-
                                                              Printed on Recycled Paper

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ues of actual emissions. The grab sam-
pling artifact is  a situation where N20 is
actually generated in grab sample contain-
ers in the presence of NOX, sulfur dioxide
(SO2), and moisture (H2O). N2O generation
approaching 200 ppm in grab sample con-
tainers has been observed.
   Realizing that accurate and reliable N2O
measurements were essential to emissions
characterization research, the Combustion
Research Branch (CRB) of EPA's Air and
Energy Engineering Research Laboratory
(AEERL) initiated  a program to concur-
rently develop grab sampling and on-line
monitoring methodologies suitable for char-
acterizing N2O emissions from various com-
bustion sources and processes. As a result
of this program, two AEERL Recommended
Operating Procedures  (ROP) were gener-
ated.  ROP No.  45: "Analysis of Nitrous
Oxide from  Combustion Sources" details a
gas chromatography/electron capture de-
tector (GC/ECD) method suitable for grab
sample analysis as well as on-line monitor-
ing. ROP No. 56: "Collection of Gaseous
Grab Samples from Combustion  Sources
for Nitrous  Oxide Measurement" details a
grab sampling method suitable for collect-
ing gaseous grab samples from combus-
tion sources to screen N2O emissions. This
report documents  the approach and re-
sults obtained while developing these pro-
cedures.

Analytical Method
   The GC/ECD backflush method devel-
oped was found to be suitable for measur-
ing N2O from  a variety of combustion
sources and applications. In addition, the
method was found to  be equally suitable
for on-line monitoring or grab sample analy-
sis. Analytical interferences, present in com-
bustion  process effluents, were  negated
through the use of a  backflushing tech-
nique.  The backflushing  method uses a
single, 10-port  valve  to  divert/direct the
flow of carrier and sample gas  streams
through the chromatographic system. This
technique employs a precolumn to isolate
the analyte of interest  from slower eluting
interferences such  as  SO2 and moisture.
Once the analyte  of interest has eluted
from the precolumn to the secondary ana-
lytical column, the carrier gas flow through
the precolumn  is  reversed, flushing the
undesirable  components  from  the
precolumn. Other common flue gas com-
ponents—oxygen, carbon monoxide (CO),
CO2, NOX,  total unburned  hydrocarbons
(THCs), and ammonia (NH3)—were found
not to interfere  with the  analytical proce-
dure.
   To eliminate the need for manual valve
switching, an air actuator, controlled by the
GC electronic hardware, was used. Electri-
cally energized solenoid valves were used
to control actuator operation. The valving
system was automated by interfacing the
GC and integrator to a timed event control
module that converted digital commands
from the integrator to time controlled elec-
trical  switches.  The  integrator could be
programmed to turn the solenoid valves on
or off at specific times. The solenoid valves,
when actuated, allowed compressed air to
pressurize the air actuator. When  pressur-
ized,  the air actuator rotates the 10-port
valve to the desired position.
   The developed system is also  capable
of unattended, continuous operation, by
incorporating the programmed timed events
into a separate BASIC program capable of
loop functions. At the end of the analytical
run, the system is capable of automatically
re-initiating the sequence of timed events.
Using this  method for on-line monitoring
allows a semicontinuous measurement
approximately every  8 min.  The system
can be easily incorporated into most con-
tinuous emission monitoring sample deliv-
ery/conditioning systems,  with the only
requirements being the removal of particu-
late and moisture from the sample stream
by a refrigeration condenser. The sample
stream should be diverted to the analytical
system before further moisture condition-
ing by a desiccant. Figure 1 is a schematic
diagram of  the automated system.
   N2O is quantified  from the linear rela-
tionship between  N2O concentration and
integrated peak area. A least squares lin-
ear regression of the calibration variables
is used to establish the linear relationship.
To improve quantitative accuracy as well
as expand the linear range of quantitation,
alternative mathematical approaches to lin-
earize detector response were investigated.
The  linear  regression approach  enables
the determination of  quantitative  bias on
an absolute basis. With this approach, er-
ror can be reported as less than a certain
concentration, often reported as a  percent-
age of full scale or as deviation  from the
true or known value. A problem arises in
that the estimated bias for low concentra-
tions will be very large relative to the mea-
sured or true concentration. By performing
a linear regression of natural log (In) trans-
formed calibration variables, error is ca-
pable of being reported on a relative basis.
   Table 1  compares the relative bias of
calculated concentrations (relative to the
true concentration) using both quantitative
approaches. The linear regression of the
transformed calibration variables  was ef-
fective in minimizing  the relative  error of
calculated concentrations. Less than 10%
bias was observed over the entire quanti-
tative range as opposed to as  much as
700% relative bias for the non-transformed
quantitative approach.
   The automated, on-line GC/ECD sys-
tem was evaluated extensively on a num-
ber of diverse EPA/AEERL fossil fuel
combustion test facilities. Initially, the ana-
lytical system was used exclusively during
the development of the N2O grab sampling
method. On-line and grab sample mea-
surements were performed on gases gen-
erated by the Flue Gas Simulation System
(FGSS). The on-line concentrations mea-
sured were compared to grab sample mea-
sured  concentrations to assess artifact
generation.  For AEERL's Gas  Cleaning
Technology Branch (GCTB), the N2O moni-
toring system was used to measure N2O
emissions resulting from the combustion of
various coals during parametric SO2 re-
moval testing.  The  N2O concentrations
measured 0.5-10 ppm.
   During these tests, quality control span
checks were performed nearly every hour
over the 8-h test period. The quality control
checks were used to assess method ana-
lytical bias and  precision  over the course
of the entire test period. The average bias
observed (2.9%) was well within the tar-
geted level of less than 15%. Similarly, the
precision observed (2.7%), expressed as
percent relative  standard deviation (RSD),
was well  within  the targeted level of less
than 10%.

Grab Sampling Method
   The discovery of the N2O sampling arti-
fact attenuated  the need for a standard-
ized, reliable sampling method in order to
accurately assess the N2O emissions from
fossil  fuel combustion sources.  Realizing
that consistently eliminating the  sampling
artifact entirely  would be extremely diffi-
cult,  if not impossible, the AEERL/CRB
believed that minimizing N2O generation to
consistent levels within aged sample con-
tainers would be suitable to screen for high
N2O-emitting combustion sources. Specifi-
cally,  AEERL researchers felt that consis-
tently  minimizing  N2O  generation within
grab sample containers to  less than 10
ppm over a  1-2  week period would be
more  than acceptable to screen for high
N2O-emitting fossil  fuel  combustion
sources.  The screening technique  could
then be used to direct on-line monitoring
efforts.
   The screening of intended fossil fuel
combustion sources would require the vol-
untary cooperation of commercial and re-
search  combustion  facilities  alike.
Therefore, the grab sampling equipment
and technique must be easy  to use and
pose  minimal imposition to those partici-

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                                                      To CEMs
                                                                          12:fr
                                                                        Analytical':
                                                                         Column —'-
A/2O
Span
Gas

Air
or
House
Air

P5
Carrier
Gas
                                                                                                     Sample Event
                                                                                                     Control Module
                                                                                                     Integrator
                   (') 1 ft = 0.305 m
Figure 1.  Automated, on-line GC/ECD N2O monitoring system.
Table 1. Comparison of Relative Bias Using Differing Mathematical Approaches
                        Linear Regression
                     (Untransformed Variables)
  Linear Regression
(Transformed Variables)
N2O Known
ppm
0.5I
0.97
1.99
5.03
9.85
19.4
40.4
80.1
128
N2O Calc.
ppm
-3.11
-2.13
-0.40
4.58
11.35
23.18
45.74
83.36
123.68
% Bias
-705. 1
-319.6
-120.1
-8.9
15.2
19.5
13.2
4.1
-3.4
N2O Calc.
ppm
0.47
0.99
2.02
5.36
10.41
20.11
40.45
77.74
120.79
% Bias
-8.6
2.1
1.5
6.6
5.7
3.7
0.1
-2.9
-5.6
pating  in screening surveys.  Specifically,
the grab sampling method should not re-
quire a great degree of sampling exper-
tise. In  addition, the grab sample should
be obtainable in a manner compatible with
commonly employed continuous emission
monitoring (CEM) sample delivery systems.
   SO2, NOX,  and H2O,  components
present in most fossil fuel combustion pro-
cess emissions, were identified as the key
artifact reactants. The selective removal of
any  or all of these reactants was targeted
as an  approach to eliminating the  sam-
pling artifact. The use of a desiccant alone,
phosphorus pentoxide (P2O5), was effec-
tive  in drastically reducing the artifact gen-
eration but was unable  to  eliminate  it
completely. A calcium hydroxide/sand mix-
ture was found to be extremely effective at
neutralizing high concentrations of SO2.
   The method  developed was designed
to be  used compatibly  with  continuous
emission monitoring sample delivery/con-
ditioning systems or as a stand-alone pro-
cedure. Specifically, the developed method
uses reactant-specific dry sorbents  to re-
move the gaseous components, SO2 and
H2O, to the degree that H2O generation in

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stored sample containers  (1-2 weeks) is
consistently minimized to less than 10 ppm.
Sequentially, SO2 is neutralized and H2O
removed from a fossil fuel combustion pro-
cess flue gas sample stream before enter-
ing a Teflon-lined stainless steel container.
The neutralization of SO2 requires H2O in
the flue gas stream. Therefore, the flue
gas sample must be collected upstream of
any moisture conditioning devices such as
condensers and/or desiccants that may be
present in CEM sample delivery/condition-
ing systems.
   The flue gas sample is extracted from
the combustion source using a vacuum
pump which  pushes the gaseous-sample
                     through  the two-cartridge, solid  sorbent
                     system and ultimately through the grab
                     sample container or "sample bomb." The
                     sampling system was designed to  be used
                     upstream of any pollution control equip-
                     ment  or on combustion  facilities where
                     pollution control equipment did not exist.
                     The grab  sampling system is shown in
                     F:igure 2.
                        During  the  development of this sam-
                     pling method, tests were conducted to de-
                     termine the fossil fuel combustion  process
                     flue gas nitric oxide (NO), SO2, and H2O
                     concentration ranges where N2O  genera-
                     tion in aged (1-2 week) samples would be
                     consistently minimized to less than  10 ppm.
                     This method was found suitable for use on
         combustion systems with flue gas concen-
         trations in the following ranges:
             SO2: 0-2,500 ppm
             NO: 0-1,000 ppm
             H2O: 5-25% (by volume)
            These flue gas concentration ranges
         were verified  under  simulated and actual
         combustion conditions. An example of the
         method's effectiveness to  minimize  N2O
         generation is shown in Figure 3. Flue gas
         components of CO, CO2, and THCs,  typi-
         cally present in fossil fuel combustion pro-
         cess streams, were found not to interfere
         with sampling method performance. Other
         common flue gas components, such as
         hydrogen chloride (HCI) and NH3, were not
         evaluated and may act as interferences.
                                                                              Inlet
         From Stack
                                                                                                      Outlet
                                                                 H2O Sorbent
                                                                    Sample Container
                                                                                                            Meter
                   Sample Pump
Figure 2. Sorbent/sample container schematic.
                                                Flue Gas Simulation System
                                         A/;?O Artifact Generation of Samples Collected
200


150
                   §:  so
                                       165 ppm
                                                       0.8 ppm
                                                  0.5 ppm
                           I Without Sorbents
                           \Sample Flow = 11 LPM
                          Sample Bombs Aged 6 Days

•                               With Sorbents (X10)
                               Sample Flow = 9 LPM
On-Line N#O Cone.
(X10)
                    Sorbent (10:1 Sand, Ca(OH)2 and P&$
                    1,200 ppm SO2, 600 ppm NO, 10% Moisture
                    NgO Initial = 0.5 ppm
Figure 3. Comparison of on-line N2O concentration to N2O sample container generation with and without use of sorbents.
                                                                       •fru.S. GOVERNMENT PRINTING OFFICE: 1*93 - 730-071/80024

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J.V. Ryan and SA /Cams are with Acurex Environmental Corp., Research
  Triangle Park, NC 27709.
William P. Linak  is the EPA Project Officer (see below).
The complete report, entitled "Development of Sampling and Analytical Methods
  for the Measurement of Nitrous Oxide from Fossil Fuel Combustion Sources,"
  (Order No. PB93-194330; Cost: $17.50; subject to change) will be available
  only from
        National  Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at
        Air and Energy Engineering Research Laboratory
        U.S. Environmental Protection Agency
        Research Triangle Park, NC 27711
   United States
   Environmental Protection Agency
   Center for Environmental Research Information
   Cincinnati, OH 45268

   Official Business
   Penalty for Private Use
   $300
     BULK RATE
POSTAGE & FEES PAID
         EPA
   PERMIT No. G-35
   EPA/600/SR-93/088

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