Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories

N2O EMISSIONS FROM ADIPIC ACID
AND NITRIC ACID PRODUCTIONA C K N O WL E D G E M E N T S
This paper was written by Heike Mainhardt (ICF Incorporated) and reviewed by Dina Kruger (USEPA).

ABSTRACT
Nitrous oxide (N2O) is generated as a by-product during the production of adipic acid and nitric acid. The mainuse for adipic acid is as a component of nylon-6/6; thus production trends are closely correlated with nylon
consumption trends. Worldwide, there are very few adipic acid plants. The U.S. is a major producer with threecompanies in four locations accounting for approximately forty percent of world production. Other producing
countries include Brazil, Canada, China, France, Germany, Italy, Japan, Korea, Singapore, Ukraine, and United
Kingdom. Most of these countries have only one adipic acid plant. Nitric acid is used primarily to make synthetic
commercial fertiliser. Worldwide, the number of nitric acid plants is somewhat uncertain. Estimates range from255 to 600 plants (Choe et al., 1993; Bockman and Granli, 1994). In 1990, adipic acid production was the largest
source of industrial N2O emissions. As of 1999, industrial sources report that all major adipic acid producers
have implemented N2O abatement technologies (Reimer, 1999). As a result, nitric acid production is currently
believed to be the largest industrial source of N2O emissions.
The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC Guidelines) outline astraightforward method for estimating emissions from both adipic acid and nitric acid, in which an emission
factor is multiplied by production data. Thus, the key factors regarding the accuracy of the estimate will be thequality of the emission factor and activity data used.
The accuracy and precision of N2O emission factors are directly correlated with the number of samples and thefrequency of sample collection. Countries have three broad options for obtaining emission factors: continuous
monitoring, periodic sampling, and the use of default factors. The chosen approach will depend on the desired
level of accuracy and resource availability, as well as plant-level characteristics such as the range of process
variability and the state of technology (including N2O abatement technology). The IPCC recommends using
plant-specific emission factors where possible.
Continuous emission monitoring is the most accurate approach, because it can account for the variability in theoverall process and directly capture the effects of control measures. It can be costly, however. The calculation ofplant-specific emission factors can be an accurate alternative to continuous monitoring if based on periodic
sampling under process conditions that are representative of routine operation. Ideally, plants should determine
the frequency of their sampling programme by conducting very frequent monitoring for a period of time in orderto determine the range of variability in the overall process. If periodic sampling is not feasible, the IPCC provides
default emission factors for both adipic acid and nitric acid production. These default emission factors, which are
currently used by most countries, introduce a large degree of uncertainty because they represent a relationshipbased on information from only a few plants.
Adipic acid and nitric acid production data are necessary to estimate N2O emissions regardless of the selected
estimation method. Countries should obtain plant-level data on an annual basis. Where such data are unavailable,
it appears that some countries have used plant capacity information as a proxy. However, since these data do not
represent actual annual production, they introduce uncertainty into the estimate. Producers may consider adipic
acid and nitric acid production data proprietary. Thus, it may be necessary to ensure that these data are notreleased to the public, or to publish them in a way that ensures that individual plants are not identified.
Reporting of these sources is quite clear, compared to other industrial process gases, because the IPCC
Guidelines call for adipic acid and nitric acid emissions to be reported individually.
Quality assurance and quality control activities should occur at several points in the emission estimation process. At
the plant level, key elements should include internal quality control on plant level measurements and production
data, documentation of data and methods for reviewers. The inventory agency must ensure the accuracy of plant
submissions as well as the compiled inventory. The agency will also be responsible for providing documentation andreporting sufficient information to the United Nations Framework Convention on Climate Change (UNFCCC)
Secretariat. One or more different types of external reviews and audits may also be appropriate.

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Background Paper

1

INTRODUCTION

1.1
1.1.1

Nature, magnitude, and distribution of source
Overview of N 2 O emissions

The main sources of industrial anthropogenic N2O potential emissions are adipic acid and nitric acid production,
each of which is discussed below.
Adipic acid is a white crystalline solid used primarily as the main constituent of nylon (nylon-6/6), representing
about half of the nylon molecule. It is also used in the manufacture of some low-temperature synthetic lubricants,
synthetic fibers, coatings, plastics, polyurethane resins, and plasticizers, and to give some imitation food productsa "tangy" flavour. In 1990, adipic acid production was the largest source of industrial N2O emissions. As of 1999,
industrial sources report that all major adipic acid producers have implemented N2O abatement technologies and,as a result, this source has been decreased substantially (Reimer, 1999). Adipic acid production also generates
emissions of non-methane volatile organic compounds (NMVOCs), carbon monoxide (CO), and nitrogen oxides (NO x).
Since the main use for adipic acid is as a component of nylon, adipic acid production trends are closely
correlated with nylon consumption trends. Rising demand for engineering plastics has sparked expansion inexisting adipic acid capacity in North America and Western Europe, as well as new facilities in the Asia-Pacificregion. Global adipic acid production is expected to total nearly 2.7 million metric tons (6 billion pounds) in2000 (CW, 1999) as compared to 1.8 million metric tons (4 billion pounds) in 1995 (CMR, 1998a; SRI, 1997).
Economic drivers include new housing starts and nylon engineering resins in the automotive and electronics
industries (CMR, 1998a).
Worldwide, there are very few adipic acid plants. The U.S. is a major producer with three companies in four
locations accounting for approximately forty percent of world production. Other producing countries include
Brazil, Canada, China, France, Germany, Italy, Japan, Korea, Singapore, Ukraine, and United Kingdom. Most ofthese countries have only one adipic acid plant except China (3), Germany (2), Japan (2), and U.S. (4) (SRI
Consulting, 1998).
Although global adipic acid demand is expected to increase, N2O emissions from this source are expected tocontinue to decrease substantially as they have since 1996. As reported by industrial sources, the decrease is a
result of nearly all adipic acid producers’ installation of N2O abatement technologies. Overall, N2O abatement isestimated to have improved from approximately 32% in 1990 to approximately 90% in 2000 (Reimer, 1999).
Abatement technologies’ current efficiency range is 90 to 99 percent reduction of N2O emissions.
Nitric acid (HNO3) is an inorganic compound used primarily to make synthetic commercial fertiliser. The raw
material is also used for the production of adipic acid and explosives, metal etching, and in the processing of
ferrous metals. Now that most adipic acid plants have implemented abatement technologies, nitric acidproduction is currently believed to be the largest industrial source of N2O emissions.
Since the main use for nitric acid is as a component of fertiliser, nitric acid production trends are closely
correlated with fertiliser consumption trends. Future trends in fertiliser production vary greatly depending on theregion. In parts of Western Europe, the use of nitrogen-based fertilisers is decreasing due to concerns overnutrient run-off. Other regions, such as Asia, South America, and the Middle East are building up their nitrogen
fertiliser production capacities (CMR, 1998b). In the U.S, fertiliser production is projected to increase by 4 percent
by 2000 (FAO, 1998). Other factors to consider are government programmes, weather conditions and general
economic growth. As a result of having many variables, it is very difficult to project future nitric acid production.
Worldwide, the number of nitric acid plants currently in operation is somewhat uncertain. Bockman and Granli(1994) report that there are approximately 500 to 600 nitric acid plants. While Choe et al. (1993) place thenumber at around 255 plants. This uncertainty may be due to the fact that nitric acid plants are often part of larger
production facilities, such as fertiliser or explosive manufacturing. As a result, only a small volume of nitric acidis sold on the merchant market.
Nitrous oxide emissions from nitric acid production will be influenced by the degree to which emission control
efforts are applied in both new and existing nitric acid plants. Since many nitric acid production facilities are
between 20 and 30 years old (CMR, 1995), there appear to be opportunities to install or update emissions control
technologies. However, it is unclear whether these improvements are actually taking place.

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1.1.2

N 2 O generation process

Table 1 summarizes factors that influence N2O generation for adipic and nitric acid production. Both production
processes are described in detail below.
TABLE 1FACTORS THAT POTENTIALLY INFLUENCE N2O GENERATION
FactorSpecific Examples/Description

Adipic Acid Production
Oxidizing Agent

Nitric Acid Oxidation vs. Hydrogen Peroxide Oxidation (currently this is not a costeffective commercial option)

N2O Abatement Technologies

Thermal destruction, catalytic destruction, recycle to adipic acid, and recycle to nitricacid. Technologies currently range from 90 to 99 percent N20 emission reduction.

Abatement System Utility

The total reduction in N2O emissions from abatement technology depends on thesystem’s tility rate. Therefore, the technology’s N20 destruction factor should be
multiplied by an abatement system utility factor in order to account for any down time ofthe emission abatement equipment (i.e., time the equipment is not operating).

Nitric Acid Production
Type of Facility

Nitric acid plants are often part of a larger production facility, such as fertiliser or
explosive manufacturing, which can cause significant operating variations between
facilities. Emissions will vary substantially depending on the specific type of nitric acidplant (e.g., high pressure, medium pressure, double absorption; see Table 3).

Production Factors

Catalyst type, catalyst age, metal gauze type, and reactor operating conditions. In general,
N2O generation decreases with increasing gauze temperature, and increases withincreasing inlet ammonia concentration (Choe et al., 1993).
1

N2O Abatement Technologies

BASF N2O Decomposition (catalytic destruction) , Norsk Hydro Agri (processintegrated N2O destruction), and thermal destruction.

NOx Abatement Technologies

Nitric acid plants with NOx control measures impact N2O emissions. Emission factors up
to 19 kg N2O/tonne nitric acid have been reported for plants not equipped with nonselective catalytic reduction (NSCR) technology (Choe et al., 1993). Choe et al. (1993)
estimate that approximately 80% of nitric acid plants do not employ NSCR technology.
Also, some nitric acid plants may recycle N2O for use in other phases of the facility.

Abatement System Utility

Please see abatement system utility explanation above.

Manufacturing process of adipic acid: Adipic acid is a dicarboxylic acid manufactured by a two-stage process.
The first stage of manufacturing usually involves the oxidation of cyclohexa2 to form a cyclohexanone/cyclohexanol
mixture. Generally, the second stage involves oxidizing this mixture with nitric acid to produce adipic acid. N2O isgenerated as a by-product of the nitric acid oxidation stage, as illustrated below:(CH2)5CO + (CH2)5CHOH + wHNO3 ⇒ HOOOC(CH2)4COOH (Adipic Acid) + xN2O + yH2O
Process emissions from the production of adipic acid will vary with the types of technologies and level ofemissions controls employed by a facility. Recently, researchers at Nagoya University developed a new method
for adipic acid production. The Nagoya process substitutes 30 percent aqueous hydrogen peroxide for nitric acid,producing adipic acid in over 90 percent yield and eliminating N2O as a by-product (Sato, 1998). However,commercial application of this process will depend on finding cheaper ways to produce hydrogen peroxide.
A facility can employ a number of activities to control emissions. These activities include implementing thermaland catalytic destruction technologies, and recycling activities. Table 1 summarizes factors that influence N2O
generation from adipic acid production.
Manufacturing process of nitric acid: The production of nitric acid (HNO3) generates nitrous oxide (N2O) as aby-product of the high temperature catalytic oxidation of ammonia (NH3).
1

Currently unavailable to other nitric acid producers.

2

Or sometimes cyclohexanone.

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Background Paper

Nitric acid production involves three distinct chemical reactions:
4NH3 + 5O2 ⇒ 4NO + 6H2O
2NO + O2 ⇒ 2NO2
3NO2 + H2O ⇒ 2HNO3 + NO
Although nitrous oxide generation during the production of nitric acid is not well documented. The steps ofnitrogen oxidation are considered to be potential sources of N2O. Nitric oxide (NO), an intermediate in the
production of nitric acid, readily decomposes to N2O and nitrogen dioxide (NO2) at high pressures for atemperature range of 30-50°C (Cotton and Wilkinson, 1988). Table 1 summarizes factors that influence N2O
generation from nitric acid production.

1.2

The current state of inventory methodologies

The IPCC Guidelines describe a simple method for estimating N2O emissions from both adipic and nitric acidproduction, in which an emission factor is multiplied by production data to yield an emission estimate. The IPCC
Guidelines encourage plant level measurement programmes, but provide default emission factors for both sources.
Currently, most Parties appear to be using these default values as opposed to conducting monitoring programmes.

2

METHODOLOGICAL ISSUES

2.1

Selection of the estimation method

The IPCC guidelines outline a straightforward method for estimating emissions from both adipic acid and nitricacid, in which an emission factor is multiplied by production data. Thus, the key factor regarding the accuracy ofthe estimate will be the quality of the emission factor and the activity data used. Both of these are discussed below.

2.2

Emission factors

The accuracy and precision of N2O emission factors are directly correlated with the number of samples and thefrequency of sample collection. Generally, countries have three broad options for obtaining emission factors:
continuous monitoring, periodic sampling and the use of default factors. The chosen approach will depend on thedesired level of accuracy and resource availability, as well as plant-level characteristics such as the range ofprocess variability and the state of technology. The IPCC recommends using plant-specific emission factors
where possible, and notes that the small number of adipic acid plants per country should make it possible toobtain such data for this source. As a general rule, sampling and analysis should be undertaken when a plantmakes any significant process changes that would affect the generation rate of N2O.

2.2.1

Continuous emissions monitoring

Continuous emissions monitoring is the most accurate approach, because it can account for the variability in theoverall process and can directly capture the effects of control measures. Continuous emissions monitoring can be
performed using a gas chromatograph with an automated sampling system, appropriate detector (e.g., thermal
conductivity), and a device to measure volumetric flowrate. Samples of the vented gas stream taken as frequently
as every few minutes, and coupled with the volumetric flowrate, provide a direct measure of the mass emission rate.
This approach can be very accurate when quality assurance and quality control (QA/QC) procedures are performed.
It will account for abatement technology variability and any other factors that affect emissions. The major
shortcoming of this approach is that it can be expensive in terms of the installed capital cost of the equipment and theoperating costs, especially costs associated with inspection, QA/QC, and maintenance of the equipment.

2.2.2

Periodic sampling and analysis

The calculation of a plant-specific emissions factor, which relates the mass rate of N2O generation to the
production rate of adipic acid or nitric acid (e.g., tonne of N2O/tonne of adipic or nitric), can be an accuratealternative to continuous monitoring if it is based on periodic sampling. The sampling must be performed underprocess conditions that are representative of routine operation. If process changes are subsequently made that willaffect the generation rate of N2O, then sampling should be performed again to quantify emissions under the new

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conditions. Otherwise, scaling an emissions factor based on non-representative sampling over the period of a year
will introduce error.
Ideally, plants should determine the frequency of their sampling programme by conducting continuous or veryfrequent monitoring for a period of time in order to determine the range of variability in the overall process. Suchfrequent monitoring should also be undertaken when new technologies (e.g., control measures) are employed, inorder to determine the new range of variability and account for the common set-backs associated with the start-up
phase of a new technology.
Periodic sampling and analysis are performed by taking samples of the vent stream in an appropriate container,such as glass flasks, flexible bag, or stainless steel canister, and transporting it to a laboratory for analysis of N2O
concentration. At the time the sample is taken, the volumetric flow rate is determined using an appropriate
measuring device, such as a gas volume meter, pitot tube, rotameter, etc. The concentration multiplied by theflowrate provides a measure of the mass rate of N2O, which can be applied to the rate of production of adipic
acid or nitric acid for the whole year.

2.2.3

Default emission factors

If periodic sampling is not feasible, the IPCC provides default emission factors for both adipic acid and nitricacid production. These default emission factors, which are currently used by most countries, represent a
relationship based on information from a few plants and laboratory experiments. Thus, the current default
emission factors introduce a large degree of uncertainty in the emission estimates. The key to minimizing thisuncertainty is sampling and analysis to determine an appropriate emission factor at each specific plant.
Adipic Acid Default Emission Factors
The current IPCC default emission factor for adipic acid is 300 kg of N2O per tonne of product. This factor wasdeveloped based on experiments (Thiemens and Trogler 1991) that attempt to replicate the industrial process
and, thereby, measure the reaction stoichiometry for N2O production in the preparation of adipic acid. Reimer etal. (1992) support this factor as being representative of measured industrial rates. Furthermore, Japaneseemissions have been measured at 264 kg of N2O per tonne of product, which is consistent with this value (Japan
Environment Agency, 1995).3 However, because N2O emissions are controlled in many adipic acid production
facilities, the amount of N2O that is actually released will depend on the level of controls in place at a specificplant. Where N2O control technologies are in use, the IPCC Guidelines recommend the use of plant-specific data.
In addition to the IPCC Guidelines’ current default emission factor for adipic acid production, Table 2 provides
default values for abatement technology destruction and abatement system utilization.
Nitric Acid Default Emission Factors
Currently, N2O emission estimates for nitric acid production are highly uncertain, due to a lack of information on
manufacturing processes and emission controls. The IPCC default emission factor range of 2 to 9 kg of N2O per
tonne of nitric acid produced is correspondingly large. In addition, although there are not many known abatement
technologies specifically directed at removing N2O at nitric acid plants, existing control measures for otherpollutants have impacts upon N2O emissions. Table 3 shows the IPCC default factors for this source.
It is important to note that several documents give emission factors up to 19 kg N2O/tonne nitric for plants not
equipped with non-selective catalytic reduction (NSCR) technology (Choe et al., 1993; Olivier, 1996; Oonk,
1996.). Furthermore, Choe et al., estimate that approximately 80 percent of the nitric acid plants worldwide do
not employ NSCR technology. Since most Parties appear to be using the IPCC default values (of 2-9 kg
N2O/tonne nitric) as opposed to conducting monitoring programmes; it seems the current estimates of N2Oemissions may be underestimated.

3

With regards to the Japan Environment Agency value (264 kg N2O/tonne adipic acid) provided in the Revised
1996 IPCC Guidelines, it is believed that this manufacturer uses oxidation of pure cycolhexanol (alcohol),instead of a ketone-alcohol mixture (Reimer, 1999). This is the only plant known to use this method.

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TABLE 2DEFAULT FACTORS FOR ADIPIC ACID PRODUCTION
Production Process

N2O Generation Factor

Notes

Nitric Acid Oxidation

300 kg/tonne adipic acid1

Uncertainty = ± 10% (based on expert judgement). The
uncertainty represents a variability in N2O generation due todifferences in the composition of the cyclohexanone andcyclohexanol feedstock (i.e., ketone (K) and alcohol (A)) thatare used by different manufacturers. Higher K content results
in increased N2O generation, whereas higher A content resultsin less N2O generation (Reimer, 1999). An individual plantshould be able to determine the production of N2O (based on
HNO3 consumption) within 1%. The range of 300 kg ± 10%
encompasses the variability from pure ketone to pure alcohol
feedstocks, with most manufacturers somewhere in the
middle.2

Abatement Technology

N2O Destruction Factor3

Notes (Uncertainty estimates are distinct from destruction
factor ranges)

Catalytic Destruction

90 – 95%

Uncertainty = ± 5% (based on expert judgement).
Manufacturers known to employ this technology include:
BASF (Scott, 1998), and DuPont (Reimer, 1999).

Thermal Destruction

98-99+%

Uncertainty = ± 5% (based on expert judgement).
Manufacturers known to employ this technology include:
Asahi, DuPont, Bayer, and Solutia (Scott, 1998).

Recycle to Nitric Acid

98-99+%

Uncertainty = ± 5% (based on expert judgement).
Manufacturers known to employ this technology include:
Alsachemie (Scott, 1998).

Recycle to Adipic Acid

90 – 98%

Uncertainty = ± 5% (based on expert judgement). Solutia will
be implementing this technology around 2002. (Scott, 1998).

Abatement System

Utilisation Factor4

Notes

Catalytic Destruction

80-98%

Note that these default values are based on expert judgement
and not industry supplied data or plant specificmeasurements.
In the first 1-5 years of the abatement technology
implementation, the utilization factor tends to be at the lower
end of the range. Lower utility of the equipment typicallyresults because of the need to learn how to operate theabatement system and because more maintenance problems
occur during the initial phase. After 1-5 years, the operating
experience improves and the utilization factor would tend to
be at the high end of the range.

Thermal Destruction

95-99+%

See note above

Recycle to Nitric Acid

90-98+%

See note above

Recycle to Adipic Acid

80-98%

See note above

1

Thiemans and Trogler, 1991.

2

With regards to the Japan Environment Agency value (264 kg N2O/tonne adipic acid) provided in the Revised 1996 IPCC Guidelines, it
is believed that this manufacturer uses oxidation of pure cycolhexanol (alcohol), instead of a ketone-alcohol mixture (Reimer, 1999).
This is the only plant known to use this method.

3

The destruction factor (which represents the technology abatement efficiency) should be multiplied by an abatement system utility
factor. NOTE: This range is not an uncertainty estimate.

4

Reimer, Ron, 1999. Personal communication between Ron Reimer of DuPont, USA and Heike Mainhardt of ICF, Inc., USA. May 19,
1999.

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TABLE 3IPCC DEFAULT EMISSION FACTORS FOR N2O FROM NITRIC ACID PRODUCTIONCountry

Emission Factor

Referencekg N2O/tonne nitric acid
USA

2-9a

Reimer et al., 1992

Norway - modern, integrated plant<2

Norsk Hydro, 1996

- atmospheric pressure plant

4-5

Norsk Hydro, 1996

- medium pressure plant

6-7.5

Norsk Hydro, 1996

2.2-5.7

Japan Environment Agency, 1995

Japan
a

Emission factors up to 19 kg N2O/tonne nitric acid have been reported for plants not equipped with non-selective catalytic reduction
technology (Choe et al., 1993; Olivier, 1996; Oonk, 1996.).

Furthermore, in addition to the IPCC Guidelines’ current default emission factors for nitric acid production,
Table 4 provides examples of when to apply specific default values. The table also provides default values forabatement technology destruction.

TABLE 4DEFAULT FACTORS FOR NITRIC ACID PRODUCTION
Production Process

Notes

N2O Generation
Factor(kg N2O/tonne
HNO3)

Canada•plants without NSCR•

plants using NSCR

plants without NSCR•

plants using NSCR

Based on an average emissions rate for plants of European design.

<23

The N2O generation factor accounts for N2O destruction by NSCR.
Uncertainty = ± 10% (based on expert judgement).

9.54

An estimated 80% of HNO3 plants do not use NSCR systems (Choe,
et al., 1993).

2

The N2O generation factor accounts for N2O destruction by NSCR.
Industry indicates a range of 1.12 to 2.5 kg N2O/tonne HNO3, field
experts have indicated that the lower end of the range is moreaccurate (Choe, et al., 1993; Collis, 1999). A factor of 2 wasselected as a conservative default. An estimated 20% of HNO3
plants use NSCR systems (Choe, et al., 1993). Uncertainty = ± 10%(based on expert judgement)<25

Norsk Hydro developed a state of the art reactor design in whichemissions of N2O are reduced in a process-integrated manner. Thereis only one installation operational of this type (Oonk, 1999).

1

USA
•

8.52

Norway•process-integrated N2O
destruction•

atmospheric pressure
plant (low pressure)

4-56

•

medium pressure plant

6-7.57Japan

2.2-5.78

Other Countries

8 –109•European designed, dualpressure, double
absorption plants

Emission factors up to 19 kg N2O/tonne nitric acid have beenreported for plants not equipped with NSCR technology (Choe etal., 1993; EFMA, 1994). Such a high emissions rate would most
likely apply to only a few, outdated plants.

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TABLE 4 (CONTINUED)DEFAULT FACTORS FOR NITRIC ACID PRODUCTION
NOx Abatement Technology
Non-Selective Catalytic
Reduction (NSCR)N2O Destruction
Factor80 – 90 %Selective Catalytic Reduction
(SCR)

0%

Notes
Uncertainty = ± 10% (based on expert judgement). NSCR is atypical tail gas treatment in the USA and Canada with lessapplication in other parts of the world.
SCR with Ammonia does not reduce N2O (Johnson Matthey, 1991;
Choe et al., 1993).

1

Non-Selective Catalytic Reduction (NSCR)

5

Norsk Hydro, 1996.

2

Collis, 1999.

6

Norsk Hydro, 1996.

3

Collis, 1999.

7

Norsk Hydro, 1996.

4

Choe, et al., 1993.

8

Japan Environment Agency, 1995.

9

Oonk, 1999.

2.3

Activity data

Adipic acid and nitric acid production data are necessary to estimate N2O emissions regardless of the selected
estimation method. Countries should obtain plant-level data on an annual basis so that they can apply plantspecific emission factors. Where plant-level production data are unavailable, it appears that some countries haveused plant capacity information as a proxy (this is especially the case for adipic acid production). Since thesedata do not represent actual annual production, they introduce uncertainty into the estimate.
Producers may consider adipic acid and nitric acid production data proprietary. Thus, it may be necessary toensure that these data are not released to the public, or to publish them in a way that ensures that individual plants
are not identified.

2.4

Uncertainty

Parallel to the IPCC sector-specific workshops on good practice guidance, the IPCC is completing a programmeof work on emissions inventory uncertainty. This work will result in recommendations to the UNFCCC on
approaches to assessing and managing uncertainty. During the IPCC Inventory Experts Group Meeting in Paris(October 1998), technical experts in the uncertainty programme came up with a series of questions to beanswered in the sector workshops. Specifically, the sector workshops should provide answers to these questionsin the individual source context, to inform work of the uncertainty programme on establishing a general
methodological approach. These questions are listed in the general background paper and should be answered
during the workshop for these sources.

2.5

CompletenessA review of 42 national inventories submitted to the UNFCCC Secretariat indicated that 21 countries reported on
N2O emissions from industrial processes. However, only 11 countries reported N2O emissions separately for
adipic acid and nitric acid production, and all others reported emissions as an industrial aggregate. Thus, it isdifficult to assess the completeness of current inventories.
Given that there are a relatively small number of adipic acid facilities in most producer countries, and that itshould be possible to develop plant-specific emissions estimates, complete reporting of this source should be
attainable. Complete reporting for nitric acid, however, will be more difficult given that there may beapproximately 600 plants and only a small amount of the product is sold on the merchant market.
For both sources, reporting should include qualitative and quantitative information from each industrial plant
including amount of adipic acid and nitric acid produced, relevant operating parameters (i.e., production process
and abatement technologies), and associated N2O emissions, subject to appropriate confidential businessinformation concerns.

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2.6

Other important issues

2.6.1

Emissions baselines

If measurements and sampling of N2O emissions are not available for previous years, there will be a consistency
problem in an emissions time series. This will inevitably be the case, for example, if a plant was producing adipic or
nitric acid during a baseline year but shut down before a rigorous inventory measurement programme isimplemented. The only alternative in this case is to apply emission factors developed from other plants to available
historical production data, or production estimates based on operating capacity. It is important that the emission
factors represent operating conditions in the baseline year as closely as possible. Nevertheless, emission estimates forthese plants in these years will be uncertain, and little documentation will be available for verification.

3

REPORTING AND DOCUMENTATION

3.1

Current IPCC reporting guidelines

The IPCC Guidelines are used to guide countries in the preparation and submissions of annual greenhouse gas
emissions inventories to the UNFCCC. The Guidelines establish:•

Standard tables, definitions, units, and time intervals for reporting all types of emissions;•

Necessary documentation to enable comparison of national inventories, including worksheets, major
assumptions, methodological descriptions, and enough data to allow a third party to reconstruct the inventory
from national activity data and assumptions, and•An uncertainty assessment.

N2O emissions from adipic acid and nitric acid production are reported individually in Table 2-1: Potential
Emissions from Industrial Processes, which calls for entries for each source emissions totals of carbon dioxide,
methane, nitrous oxide, precursor gases (NOX, CO, NMVOCs, SO2), HFCs, PFCs, and SF6.
N2O emissions from adipic acid and nitric acid production are reported in the IPCC Guidelines on pages 2.19
and 2.17 respectively.

3.2

Confidential business information

In most cases, detailed descriptions of how nitric acid and adipic acid producers determine N2O emissions can beevaluated based on knowledge of the process chemistry; however, validation of the actual calculations may
require access to confidential business information (CBI). For example, some U.S. producers have indicated thatthe following information is considered CBI at the company level, but not when aggregated for all companies:•

Adipic acid and nitric acid production levels, and•N2O emissions.

The issue of confidential business information may complicate the desire for clear and transparent national
reporting. An alternative is to report on the number of plants and national level production. However, in cases
where there is only one plant, plant-level production will equal national production.

4
4.1

INVENTORY QUALITY
Introduction

Inventory quality assurance and quality control (QA/QC) is a process integral to the development of a credible
inventory. A well-developed and well-implemented quality assurance programme fosters confidence in the final
inventory results regardless of the purpose and goal of the inventory. A successful quality assurance programmeis two-fold requiring internal industrial plant level procedures and external review and audit activities. Theinternal QC activities are designed to ensure accuracy, documentation and transparency. The external review
process is designed to minimise errors that occur in the preparation of emissions inventories, and reduce or
eliminate potential inherent bias from any given facility. Figure 1 outlines the flow of information and processes
followed at each step.

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Figure 1

Inventory QA/QC process
Plant

Internal QC:

Plant-level measurement and calculations

Documentation:

Plant-level information provided to the government agency, and results ofinternal QC
Government Agency

Review/QA:

Plant-level inputs

Internal QC:

Compilation of national inventory from plant-level data

Documentation:

Results of compilation and results of QA/QC

Reporting:

Official submission to UNFCCC
External Review

External Review:

External audit, stakeholders, peer and public review of inventory results,
external verification against other data etc.

Documentation:

Results of external review
UNFCCC Secretariat

External Review:

4.2
4.2.1

Requires standard format and transparency – ensure consistency with otherinventories and external data

Internal inventory QA/QC systems
Plant-level activities

Plant-Level Measurement and Sampling QC
The inventory QC procedures used at the industrial plant level will be determined in large part by plant personnel.
There are, however, certain procedures common to monitoring programmes which should be specified:•sample collection methods (including frequency, container type and preparation);•sample stability (prior to analysis);•

written standard operating procedures for sampling and analysis;•

calibration procedures (number, frequency, standard chosen, acceptance criteria);•

limits for accuracy and precision;•

method to flag suspect data, and•maintenance of records.

Plant-Level Production Data QC
Annual activity data are required to estimate N2O emissions from industrial processes. Accurate production
records should be available at the plant level.
Plant-Level Documentation
The emissions information necessary to allow a thorough analysis by the reviewing/auditing agency will include
adipic acid and nitric acid production, and the basis for estimating the emissions for unit of product.

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4.2.2

Inventory agency level activities

Inventory Agency Review (QA) of Plant-Level Information
Before accepting plant-level emissions data, the inventory agency should carry out an assessment of data quality
and sampling procedures. This type of review requires close cooperation with plant owners to obtain enoughinformation to verify the reported emissions, as discussed above. The assessment should include sample
recalculations, an examination of the representation of the data and operating conditions, and identification ofpotential bias in the methodology and recommendations for improvement.
Inventory Agency QC on Compiling National Emissions
In addition to a thorough quality assessment of plant-level data discussed above, the inventory agency should
ensure that the process of aggregating plant data to develop the national inventory undergoes quality control. Thisshould include, among other things:•

cross-referencing aggregated adipic acid and nitric acid production statistics with national totals;•

back-calculating national emissions factors from aggregated emissions and production data;•

ensuring all plants are included, and•comparison with industry trends to identify anomalies and patterns.

Inventory Agency Documentation on Compiling National Emissions•

For the N2O emission inventories, a QA/QC management plan should address the specific items needed toperform audits and reviews. When each plant provides the estimates, the details should be documented at theplant level to account for differences in the procedures among plants. Examples of the types of informationneeded for documentation and external audit include:•

a detailed description of the inventory methodology;•

identification of the input parameters that are needed and how the input parameters are obtained (measured
or estimated);•

frequency of the measurements and results of determinations of accuracy and precision for the measurements;•

an estimate or discussion of uncertainty and variability for input parameters that are estimated instead of
measured, and•when plants use a N2O emission factor relationship derived from measurements at another industrial plant,
local measurements should be taken to verify that the relationship is valid due to differences in plant
operating conditions. Countries should provide information on the origin and basis of the factor, compare itwith other published emission factors explaining any significant differences as well as attempting to placebounds on the uncertainty.

4.3

External inventory QA/QC systems

External QA activities include a planned system of review and audit procedures conducted by personnel not
actively involved in the inventory development process. The key concept is independent, objective review toassess the effectiveness of the internal QC programme, the quality of the inventory and to reduce or eliminate any
inherent bias in the inventory processes. Several types of external reviews, or audits, may be appropriate for N2Oemission inventories.
Third party audit by an accredited organization, expert, independent third party
An audit of the documentation and calculations ensures that each number is traceable to its origin. Given thatmuch of the information used in developing N2O emission estimates may be proprietary, a third party audit that
protects confidentiality may be a necessary type of review.

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Background Paper

Expert (peer) review
A detailed peer review would be appropriate when a procedure for determining N2O emissions is first adopted orrevised; it would not be needed on an annual basis. Such a review is designed to ensure that the methodology
accurately represents the plant's particular situation, is as rigorous as possible, and that the data and assumptions
used reflect the best available information.
Stakeholder review
Review by adipic acid and nitric acid producing companies, industrial organizations and government can provide
a forum for review of the methods used. This type of review would be of most value early in the inventory
process when plant-specific details are shared, which can lead to ways for some companies to improve their
methods to the levels achieved by the plants with the best methodology.
Public review
Some countries make their entire inventory available for public review and comment. This process may result ina range of comments and issues broader than those from other review processes. Confidential BusinessInformation (CBI) issues should be considered when inventories are presented for public review.

5

CONCLUSIONS

Industrial nitrous oxide (N2O) emissions are generated as a by-product during the production of adipic acid andnitric acid. In 1990, adipic acid production was the largest source of industrial N2O emissions. However, as of1999, industrial sources report that all major adipic acid producers have implemented N2O abatement
technologies (Reimer, 1999). As a result, nitric acid production is currently believed to be the largest industrial
source of N2O emissions.
The IPCC Guidelines recommend a straightforward method for estimating emissions from both adipic acid andnitric acid, in which an emission factor is multiplied by production data.
Given that N2O emissions are controlled in many adipic acid production facilities, the amount of N2O that is
actually released will depend on the level of controls in place at a specific plant. To achieve the highest accuracy,
the IPCC Guidelines recommend the use of plant-level N2O emission generation and destruction factors
developed from plant-specific measurement data. In the case of nitric acid production—with many more facilities
than adipic acid and with a much greater variation among plant types—plant-specific data may be much moredifficult to collect, and thus default factors may be needed more often.
Where adipic acid or nitric acid plant-level information is not available, IPCC default generation factors anddestruction factors should be selected based on the plant types and abatement technologies implemented. Adipic acidand nitric acid production data are necessary to estimate N2O emissions regardless of the selected estimation method.
Quality assurance and quality control activities should occur at several points in the emission estimation process.
At the plant level, key elements should include internal quality control on plant level measurements andproduction data, and documentation of data and methods for reviewers. As a quality assurance check, a country
that calculates emission estimates from plant level information (bottom-up approach) should compare thosevalues with estimates produced from national statistics (top-down approach).

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