United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 2771
Research and Development
EPA/600/S8-88/079 July 1988
&EPA Project Summary
EPA/NOAA/NASA/USDA N2O
Workshop: Volume I.
Measurement Studies and
Combustion Sources
September 15-16, 1987,
Boulder, Colorado
John C. Kramlich, Richard K. Lyon, and W. Steven Lanier
On September 15-16, 1987, the
U.S. Environmental Protection
Agency, the National Oceanic and
Atmospheric Administration, the
National Aeronautics and Space
Administration, and the Department
of Agriculture jointly sponsored a
workshop on atmospheric nitrous
oxide (NgO) at Boulder, Colorado.
This meeting follows a previous
workshop which was held at Durham,
North Carolina, on February 13-14,
1986. These meetings served a
number of purposes. One important
objective was to provide an
opportunity for a more timely
exchange of information among
researchers than would otherwise be
possible through normal technical
channels. Another major purpose
was to prioritize the research that is
needed to determine if atmospheric
N2O is a problem, and to understand
the importance of the various
sources and sinks.
The technical discussion involved
three areas: (1) measurement
approaches, (2) combustion sources
of N2O, and (3) biogenic sources of
NjO. Within each area, the focus was
on using the best current
understanding to develop the
research priorities needed to assess
the severity of the N2O problem. This
volume focuses on the first two
areas; Volume II is to focus on the
third.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
This report summarizes a workshop
on the atmospheric emission of nitrous
oxide (N20) which was held at Boulder,
Colorado, on September 15-16, 1987,
under the joint sponsorship of the U.S.
Environmental Protection Agency (EPA),
the National Oceanographic and
Atmospheric Administration (NDAA), the
U.S. Department of Agriculture
(USDA).and the National Aeronautics and
Space Administration (NASA). This was
the second such workshop; the previous
workshop was held in Durham, North
Carolina, February 13-14, 1986. The
initial Workshop was summarized in EPA
report EPA-600/8-86-035 (NTIS-PB
87-113742).
These two workshops were held as
part of EPA's effort to develop an
appropriate research plan with respect to
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N20. The atmospheric concentration of
NgO is increasing at a rate of
approximately 0.25% per year. This is a
matter of concern since t^O is one of
several trace gases which cause ozone
depletion and contribute to the
greenhouse effect. Depletion of the
ozone layer will cause increasing
amounts of solar UV radiation to reach
the Earth's surface and result in
increasing incidence of melanoma and
other health problems. There is also
concern about adverse ecological effects
associated with increased UV-B
radiation; e.g. = decreased plankton in the
oceans. Since the lifetime of NgO in the
atmosphere is more than a century, by
the time such adverse health effects
became acute it would be too late for any
useful action. Similarly, the greenhouse
effect to which N2O contributes has the
potential for causing significant climate
changes.
While there are thus substantial
reasons for concern, many aspects of the
N2
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from N20 at high temperatures. Below
1150 K, the kinetics predict that Reaction
2 dominates HCN destruction, and little
N2O is produced.
One way that HCN may be introduced
in this region is devolatilization or
gasification of char nitrogen. A second
possibility is that HCN from the primary
flame is transported into the post-flame
region by imperfect mixing. This portion
of the mechanism remains in conjecture.
Early data suggest that NOX and N20
were correlated in practical combustion
devices. Approximately 1 mole of N20
was emitted for each 4 moles of NO,..
This is an important point because, if
true, the extensive N02 data base can be
used to estimate N2O production.
An enlarged data base was presented
by Fossil Energy Research Corporation
(FERCo) which showed considerably
more scatter than had been reported in
earlier data collections. The sense of the
session was that the data base was not
yet adequate to permit a scientifically
based extrapolation of worldwide NOX
data to worldwide N20 emissions. On
this point there was some dissent. One
viewpoint was that the NOX vs. N2O
correlation could at least be used as a
rough indicator for estimating.
FERCo also presented data on the
influence of natural gas reburning on
N2O from a pilot-scale cyclone
simulator. The results showed
approximately equivalent reductions for
N2O and NOX. The facility was also
noteworthy in that it produced the
highest N20 values reported to date from
a coal-fired combustor (484 ppm).
Work on the homogeneous chemistry
of N2O in flames was presented by
researchers from Stanford and Lawrence
Berkeley Laboratory (LBL). The general
conclusion was that most of the
chemistry is sufficiently understood to
not limit our understanding of the overall
N2O problem. The current state of
chemical kinetics was reviewed. Some
interesting results from LBL showed that
the quench region near the edge of a
flat-flame burner was capable of
producing high N2O. This may explain
the low N2O emissions observed from
industrial gas flames. Finally, work from
the Chemistry Department at Western
Michigan University showed the
spectrum of products that were
generated by flame-mode and sub-
flame oxidation of HCN. This included
significant amounts of N20.
Conclusions
A general conclusion of the workshop
members is that a significant amount of
rapid progress has been made in this
relatively new area. Measurement
continues to be a problem due to the
complexity of the various approaches.
Although gas chromatographic
techniques are well developed,
considerable skill and experience are
required to obtain reliable data. Also, the
instrument does not lend itself to real-
time, on-site measurements. It is hoped
that development of spectroscopic
techniques will continue, as these
promise the eventual development of
portable, user-friendly, real-time
instruments.
A broad outline of the N2O formation
mechanism in coal flames has been
developed. The first component of the
mechanism is a means by which re-
duced nitrogen is transported
downstream of the flame zone. If the
fixed nitrogen appears as HCN within the
1150 - 1500 K temperature window,
then a significant net N2O formation can
occur via homogeneous chemistry.
The following general statement of
needs was developed as a conclusion to
the discussions:
1. Given the critical nature of the
potential problem, there is a need to
establish a scientifically defensible
data base related to combustion-
generated N2O.
2. The current data base on emission
factors is inadequate to establish the
contribution of combustion-
generated N20 to the total global
budget.
3. There is a need to establish a
broad-based coordinated com-
bustion-generated N2O program
with:
• Full-scale -- Data base
- Emission factors
- Mechanistic insight
• Pilot-scale -- Guide and
interpret
Laboratory-scale ~ Guide
and interpret
Instrumentation ~
Standardize
Most attendees favored this statement.
Some members took issue with the
second item, and felt that the data base
did allow for a crude estimation of the
global contribution of combustion to
N20. A few members disagreed with the
third item, and felt that a large program is
not warranted until it is better understooc
if N2O is actually a critical problem.
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John C. Kramlich, Richard K. Lyon, and W. Steven Lanier are with Energy and
Environmental Research Corp., Irvine, CA 92718.
Joseph A. McSorley is the EPA Project Officer (see below).
The complete report, entitled "EPA/NOAA/NASA/USDA N2O Workshop: Volume
I. Measurement Studies and Combustion Sources, September 15-16, 1987,
Boulder, Colorado," (Order No. PB 88-214 91 HAS; Cost: $14.95, 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
y.S.OFflO£LMAAj:
Official Business
Penalty for Private Use $300
EPA/600/S8-88/079
0000329 |»S
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