EN ISO 11771:2010

SLOVENSKI STANDARD
01-december-2011
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Air quality - Determination of time-averaged mass emissions and emission factors -
General approach (ISO 11771:2010)
Luftbeschaffenheit - Ermittlung von zeitlich gemittelten Massenemissionen und
Emissionsfaktoren - Allgemeine Vorgehensweise (ISO 11771:2010)
Qualité de l'air - Détermination de la moyenne temporelle des émissions en masse et
des facteurs d'émission - Approche générale (ISO 11771:2010)
Ta slovenski standard je istoveten z: EN ISO 11771:2010
ICS:
13.040.01 Kakovost zraka na splošno Air quality in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 11771
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2010
ICS 13.040.01
English Version
Air quality - Determination of time-averaged mass emissions and
emission factors - General approach (ISO 11771:2010)
Qualité de l'air - Détermination de la moyenne temporelle Luftbeschaffenheit - Ermittlung von zeitlich gemittelten
des émissions massiques et des facteurs d'émission - Massenemissionen und Emissionsfaktoren - Allgemeine
Approche générale (ISO 11771:2010) Vorgehensweise (ISO 11771:2010)
This European Standard was approved by CEN on 27 November 2010.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11771:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3
Foreword
This document (EN ISO 11771:2010) has been prepared by Technical Committee CEN/TC 264 “Air quality”,
the secretariat of which is held by DIN, in collaboration with Technical Committee ISO/TC 146 “Air quality”.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by June 2011, and conflicting national standards shall be withdrawn at
the latest by June 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

INTERNATIONAL ISO
STANDARD 11771
First edition
2010-12-15
Air quality — Determination of time-
averaged mass emissions and emission
factors — General approach
Qualité de l'air — Détermination de la moyenne temporelle des
émissions massiques et des facteurs d'émission — Approche générale

Reference number
ISO 11771:2010(E)
©
ISO 2010
ISO 11771:2010(E)
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ii © ISO 2010 – All rights reserved

ISO 11771:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Terms and definitions .2
3 Symbols and abbreviated terms .3
4 Principle .3
5 Determination of mass emission rates .4
5.1 Planning .4
5.2 Measurements .5
5.3 Calculation of mass emission rates .6
5.4 Determination of time-averaged mass emission rates.7
5.5 Uncertainty estimation.7
6 Activity data .9
6.1 Collection of activity data.9
6.2 Activity data uncertainty.9
7 Determination of time-averaged mass emission factors .10
7.1 General .10
7.2 Calculating the time-averaged emission factor .10
7.3 Uncertainty of the time-averaged emission factor.10
7.4 Aggregating emission factors.11
7.5 Uncertainty estimation of aggregates of emission factors.11
8 Quality management system requirements.11
9 Reporting.12
9.1 General .12
9.2 Test report.12
Annex A (normative) Minimum requirements for the measurement plan.13
Annex B (informative) Example of uncertainty estimation.16
Annex C (informative) Data manipulation.21
Bibliography.22

ISO 11771:2010(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 11771 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 264, Air quality, in collaboration with Technical Committee ISO/TC 146, Air quality, Subcommittee
SC 4, General aspects, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
iv © ISO 2010 – All rights reserved

ISO 11771:2010(E)
Introduction
This Intenational Standard describes the measurement procedures necessary to determine the mass
emission of substances from stationary sources. Empirically generated data are necessary to determine the
uncertainty that can be associated with a stated result and to enable the verification of emission measurement
reports.
This Intenational Standard also describes the measurement procedures necessary to determine emission
factors. An emission factor is a value that relates the quantity of a pollutant released with an activity
associated with the release of that pollutant. Emission factors are useful when the operational conditions and
time period for which they are representative is known.
Emission factors are used to calculate and report mass emissions for both emission inventory and non-
inventory uses. Inventory uses can include:
⎯ emission trading;
⎯ compiling polluting release and transfer registers;
⎯ air quality modelling;
⎯ air quality management;
⎯ compliance with national emission limits.
Non-inventory uses can include:
⎯ developing site-specific emission estimates;
⎯ developing control strategies;
⎯ risk assessments;
⎯ deciding appropriate permit limits.
The most commonly used methodology for compiling an emission inventory is to combine information on the
extent to which an activity takes place (quantified by activity data a) with representative values of the
emissions or removals per unit activity, called emission factor F. The basic equation providing the emission as
&
a mass emission rate m is given by
&
m = aF
The basic equation can be modified in some circumstances to include, for instance, emission reduction
efficiency (abatement) factors.
NOTE 1 Countries compiling inventories for reporting emissions under international agreements use methodologies
agreed upon by convention {e.g. UN FCCC, UN ECE Long-range Transboundary Air Pollution (Reference [31]), or the
UN ECE Aarhus Convention}. A common feature of all these conventions is a requirement to use good practice
methodologies when estimating and reporting emissions. This is particularly important when providing emission estimates
for base year emission inventories used in policy instruments. Good practice is usually taken to mean the use of
procedures that ensure inventories are accurate (i.e. without bias) in the sense that they are systematically neither over-
nor underestimates so far as can be judged, and that uncertainties are reduced so far as possible. Good practice guidance
does not usually specify how to establish emission factors or what information should be reported and be available to
allow broad application of emission factors. It is the goal of this International Standard to close this gap, to increase the
quality of emission inventories and to improve efficiency.
ISO 11771:2010(E)
Emission factors published in most compilations typically are:
⎯ arithmetic averages of available source emission measurement data;
⎯ based on a limited number of emission measurements;
⎯ representative of a restricted period of process operating time;
⎯ representative of a limited range of process operating conditions;
⎯ representative of a limited sample of process units commonly used.
Emission factors are numerical estimates with uncertainties that can include systematic and random
components, e.g. measurement uncertainty, fluctuations in pollutant emission control efficiency, and variability
in process operation. The numerical uncertainty associated with a particular emission factor, for a single
source, can be estimated provided that there is sufficient, high quality, source test data to estimate statistically
the underlying variability of the more important influencing factors. Uncertainty also arises from the use of an
emission factor applicable to one activity, process, technology or installation being used to represent a
situation for which it is unsuitable. In many cases, it is not possible to quantify the uncertainty introduced
through inappropriate use of emission factors, and this situation is discouraged.
Emission factors should be used with caution. Alternative means exist for estimating emissions that can be
more appropriate under some circumstances.
A material balance can provide an adequate quantification of emissions in situations where a high percentage
of material is lost to the atmosphere (e.g. carbon and sulfur in fuel, solvent loss in an uncontrolled coating
process). Material or mass balance determinations can also account for fugitive emissions not easily
measured otherwise. In contrast, material balances may be inappropriate where material is consumed or
chemically combined in the process, or where losses to the atmosphere are a small portion of the total
process throughput.
Data from frequent and representative source-specific emissions measurements or continuous emission
monitoring systems can provide measures of actual pollutant emissions from a source.
Site-specific measurement data from a limited number of emissions measurements, while improving the
certainty of the emission data, represent only the conditions existing at the time of the testing or monitoring.
To improve the estimate of longer-term (e.g. daily, monthly, yearly) emissions, conditions under which tests
occur should be representative of the source's expected range of operations.
NOTE 2 Even in the absence of representative source-specific data, emission information from process control
technique and abatement system vendors, particularly emission performance guarantees or emission measurement data
from similar equipment can still be a better source of information than source-category emission factors.
This International Standard requires the use of supporting standards not all of which are yet available.

vi © ISO 2010 – All rights reserved

INTERNATIONAL STANDARD ISO 11771:2010(E)

Air quality — Determination of time-averaged mass emissions
and emission factors — General approach
1 Scope
This International Standard specifies a generic method for the determination and the reporting of time-
averaged mass emissions from a specific installation or of a family of installations (or common source type),
using data collected by measurements, and by establishing:
⎯ mass emission rates by the simultaneous measurement of concentration and gas flow, using
standardized manual or automatic methods, and also the estimation of the uncertainty of the
measurements;
⎯ time-averaged mass emission rates using time series of mass emission rate values, their uncertainty
characteristics, and also the determination of the expanded uncertainty of the average;
⎯ time-averaged emission factors for a specific installation or of a family of installations and their associated
uncertainty characteristics;
⎯ a quality management system to assist the process of inventory quality assurance and verification.
This International Standard is applicable to the determination of emission factors for stationary sources
including emissions from industrial processes where calculation from fuel and raw material is not practical, for
greenhouse gases, and air pollutants including fine particulate material. This International Standard does not
address compliance monitoring in the context of emission control regulations.
This International Standard requires the use of measurement-based methods and calculation-based methods
that use measurement data. It covers the planning and execution of the measurement programme to collect
data, selection of sampling methods, calculation of results, estimation of uncertainty, determination of
emission factors, and the reporting of information in a form that enables users to apply them. This
International Standard specifies how to:
⎯ generate time-averaged mass emission rate data of a known quality, for a defined period of time, and a
documented set of operational conditions;
⎯ generate complete data sets representative of a known time period (i.e. a calendar year) by filling gaps in
mass emission rate data series and combining data sets numerically;
NOTE 1 Time series data can be available for only a limited elapsed period (i.e. weeks, months, or years) and can be
available only for a discrete process whereas inventories can be necessary which average over a different period (i.e. for a
calendar year).
⎯ calculate emission factors for a known time period;
⎯ calculate time-averaged emission factors of a known quality for a known source type.
The measurement of emissions from vehicular, area or fugitive sources is not specifically covered. However,
this International Standard can be used for quantification of emission factors for those sources provided that
measurements of emissions are available.
NOTE 2 Emission fluxes from fugitive and area sources can be directly measured using optical open-path techniques.
The results from these measurements can be treated in an analogous way to the measurements described in this
International Standard to determine time-averaged emissions and emission factors.
ISO 11771:2010(E)
This International Standard does not explicitly include measurement procedures that are fully described in the
referenced standards. Neither does it provide advice on the generation of activity statistics.
[5] [6]
This International Standard is compatible with ISO 14064-1 and ISO 14064-3 .
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
emission factor
ratio of the rate at which an air pollutant is emitted as a result of some activity, to the rate of that activity
[2]
NOTE 1 Adapted from ISO 4225:1994 , 3.31.
EXAMPLE The mass, in kilograms, of particulate emitted per tonne of coal burned, the mass, in kilograms, of NO
x
per tonne of clinker produced in a country per year, or the mass, in tonnes, of CO emitted per megajoule of energy
produced.
NOTE 2 Since data are usually derived for a limited range of operating conditions or periods, the conditions or periods
over which an emission factor can be considered typical or applicable are needed (see 5.2.2).
NOTE 3 Emissions refer to the set of individual substances that are emitted.
NOTE 4 An emission factor differs from a mass emission rate, the latter has specific dimensions of mass divided by
time.
2.2
good practice
set of procedures intended to ensure that reported emissions are accurate (i.e. without bias) in the sense that
they are systematically neither over- nor underestimates as far as can be judged, and that uncertainties are
reduced as far as possible
2.3
measurand
particular quantity subject to measurement
[3]
[ISO 9169:2006 , 2.1.11]
2.4
measurement system
complete set of measurement instrumentation and associated equipment used for the determination of a
specified measurand
2.5
measurement plan
document describing the data collection methodology to be used for a particular installation, the type and
quantity of data to be collected, the data processing, the quality system to be adopted, and the processes to
be used to estimate measurement uncertainty
NOTE The measurement plan describes any provisions specific either to periodic determinations of mass emissions
or emission factors by a test laboratory or to continuous mass flow measurements made by the operator of an installation.
2.6
test
technical operation that consists of the determination of one or more characteristics of a given product,
process or service in accordance with a procedure
NOTE 1 For emission measurements, a test consists of series of measurements of one measurand or of combined
measurements of several measurands.
NOTE 2 A valid test is often specified as a number of measurements (usually not less than three) that is indicative of
the process emission under observation.
2 © ISO 2010 – All rights reserved

ISO 11771:2010(E)
3 Symbols and abbreviated terms
AMS automated measuring system
A cross-sectional area of the sampling plane
a activity data
ea() sensitivity coefficient of the time-averaged activity rate
&
em() sensitivity coefficient of the time-averaged mass emission rate
F emission factor
&
m mass emission rate
p confidence level
U (y) expanded uncertainty of a measurand y at confidence level p
p
ua() uncertainty of the time-averaged activity rate
&
um() uncertainty of the time-averaged mass emission rate
u(y) standard uncertainty of a measurand y
&
V volume flow rate
v flue gas velocity
y measurand
γ mass concentration
m
4 Principle
&
The mass emission rate, m , is calculated by multiplying a measured (or calculated) mass concentration, γ ,
m
&
by a measured (or calculated on the basis of measurements) volume flow rate, V , of the flue gas, with both
being representative of the same period of time and calculated for the same reference conditions (temperature,
pressure, water vapour and oxygen content), by Equation (1):
&
&
m = γ V (1)
m
The time-averaged emission factor, F, of a measured component is generated by dividing the mass emission
&
rate, m , of the activity by a measure of the activity associated with the release (activity data a), with both the
mass emission rate and the activity data being representative of the same period of time. The basic equation
used is given by Equation (2):
&
m
F= (2)
a
Time-averaged emission factors are calculated by dividing suitably averaged mass emission rates by a
measure of the activity rate representative of the same time period. Time-averaged mass emission rates and
emission factors are quoted with the associated relevant information that describes the operational conditions
and time period for which they are representative.
The determination of the relevant measured input quantities for the calculation requires a documented
measurement plan.
The uncertainty of the mass emission rate and emission factors is determined by estimating the uncertainty of
both the measurement and the activity data.
NOTE Annex B provides additional information on the principles fundamental to ensuring that mass emission data
reported for inventory purposes give a true and fair account.
ISO 11771:2010(E)
5 Determination of mass emission rates
5.1 Planning
5.1.1 General
Before data collection commences, prepare a measurement plan that specifies the minimum data quality
requirements. The measurement plan shall also include:
a) measurement objectives including data quality objectives;
b) data collection and measurement methods to be used;
c) type, quality, and quantity of data to be collected;
d) data-processing procedures to be used to determine the time-averaged mass emission, emission factors
and associated uncertainties;
e) quality management system requirements;
f) any associated procedures that can be required to ensure that data quality meets the specified data
quality objectives;
g) reporting procedures.
The details that shall be included in the measurement plan are listed in Annex A.
[12]
NOTE General guidance on the measurement plan is available, e.g. in EN 15259 .
5.1.2 Type and quantity of data to be collected
Emission data and activity data, if required, shall be collected over the time period specified in the
measurement objective. The data shall conform to the uncertainty requirements, the other data quality
requirements specified in the quality management system, and the data-processing procedures to be used, as
specified in the measurement plan.
NOTE 1 The time period for mass emissions is typically 6 months or a year. The time period over which emission
factors are determined can depend on the time period of available activity data.
Take measurements for a known time period when the installation is operating within the known operational
bounds set in the measurement plan.
The measurements should be made at measurement sites where the data are representative of the normal
variation of the installation or process emission. The documentation accompanying the monitoring plan should
indicate how the minimum number of sampling points to be used for each parameter measured is to be
decided and how these are to be selected.
When determining the concentration of a measured component for a known time interval (i.e. by periodic
measurement), also measure the volume flow rate or any associated measurands necessary to compute the
mass emission rate.
NOTE 2 The time interval can be regular (e.g. once per month) or irregular. Measurands can include the amount,
quantity or physical property of an emission. Measurements for less than 24 h are usually made using portable equipment.
When employing an automatic measurement method for the measurand, the flue gas velocity or any
associated measurements should also be made using an automated measurement system. The uncertainty,
data capture rate, and minimum time coverage shall conform to the data quality requirements of the
measurement plan.
4 © ISO 2010 – All rights reserved

ISO 11771:2010(E)
5.1.3 Source description data
Information shall be collected describing the operational conditions and the time period, for which the emission
rate is representative. This shall be clearly documented (see A.3).
5.2 Measurements
5.2.1 General
Perform the required measurements of the components used for the determination of mass flow rate using
national or International Standards that enable the determination of the uncertainty that can be associated
with a stated result and to enable the verification of emission reports. If this requires the use of supporting
standards that are not yet available, 5.2.2 and 5.2.4 should be regarded as informative.
Clear and unambiguous instructions shall be provided for measurement personnel.
5.2.2 Determination of the mass concentration
Determine the mass concentration, γ , of the measured component in the flue gas over the sampling duration
m
specified in the measurement plan.
NOTE 1 The measurement plan can specify periodic or continuous measurements. Typical sampling durations are
30 min or 1 h. Continuous measurements can require averaging of the measured signals over the sampling duration
specified in the measurement plan.
Sampling shall be representative of the specified sampling duration taking into account the likely variability of
the process.
The measurement methods used shall have known performance characteristics.
A sufficient number of samples shall be taken to ensure that the mass concentration, γ , meets the data
m
quality objective.
NOTE 2 The performance characteristics of the method necessary to estimate the measurement uncertainty of the
result include repeatability, reproducibility, detection limit, measurement range, and cross-sensitivity. Suitable
measurement methods have been field tested to determine their performance characteristics and the expanded
uncertainty to be expected with their use — typically at the 95 % confidence level. Some International Standards,
European Standards or suitable validated national standards can meet these criteria. A selection of International Standard
reference methods for the automated measurement of common pollutants is listed in the bibliography.
Automated measurement systems (AMS) should be operated under a quality system that assures they are
installed to measure emissions to air and are capable of meeting the uncertainty requirements of measured
values specified in the measurement plan.
[7]
NOTE 3 The capability of meeting uncertainty requirements can be demonstrated by application of ISO 14956 .
[11]
NOTE 4 EN 14181 describes the calibration of AMS.
Express the result as an average of the concentration over the sampling duration specified in the
measurement plan.
5.2.3 Determination of temperature, pressure, humidity, and oxygen
Determine temperature, pressure, humidity (moisture) and oxygen, if required, using standardized
measurement methods. Sampling shall be in the same sampling plane and in close proximity to, but not
interfering with, that used for the determination of the mass concentration and gas velocity. The
measurements shall be representative of the time period of the mass concentration measurement.
NOTE Suitable standardized determinations of temperature, pressure, humidity, and oxygen are listed in the
Bibliography.
ISO 11771:2010(E)
5.2.4 Measurement of the volume flow rate
&
Determine the volume flow rate, V, by use of a standardized measurement method or by a validated
calculation procedure based on fuel composition, measured fuel amount, and measured oxygen
concentration.
The volume flow rate shall be determined for the sampling plane used for the determination of the mass
concentration.
NOTE 1 This can be achieved by measuring the flue gas velocity, v, or oxygen concentration in the same sampling
plane and in close proximity to, but not interfering with, that used for the determination of the mass concentration.
The velocity or oxygen measurement shall be representative of the time period of the mass concentration
measurement.
[28] [28] [28] [28] [29]
NOTE 2 EPA Methods 2 , 2G , 2F , 2H , and Conditional Test Method-041 are applicable methods for gas
velocity measurement. These methods can be used to measure unadjusted velocity, yaw-adjusted velocity, yaw and pitch
angle-adjusted velocity, wall effects in circular stacks or ducts, and wall effects in rectangular stacks or ducts, respectively.
Combination methods, e.g. 2GH or 2FH can also be used. For discontinuous methods, type L Pitot tubes, as described in
[1]
ISO 3966:2008 , Annex A can be used. Alternatively, other measurement devices (e.g. type S Pitot tube) can also be
used, provided that they are calibrated against standardized Pitot tubes.
The cross-sectional area, A, of the sampling plane shall be determined with known uncertainty.
The volume flow rate is the product of the flue gas velocity and the cross sectional area, A, of the sampling
plane at its point of measurement as given by Equation (3):
&
V = vA (3)
5.3 Calculation of mass emission rates
&
Calculate the mass concentration, γ , of the measured component in the flue gas and the volume flow rate, V ,
m
at the same conditions of temperature, pressure, and humidity.
If required by the measurement plan, the mass concentration and the volume flow rate shall be corrected to
the same reference conditions for the oxygen or carbon dioxide content specified.
NOTE 1 The use of common standardized conditions enables the volume-based concentration values and
corresponding volume flow rates to be multiplied together without the introduction of bias.
The results shall be expressed in SI units.
Calculate the mass emission rate by multiplying the mass concentration of the measured component in the
flue gas by the associated volume flow rate of the flue gas according to Equation (4):
&
m& = γ V (4)
m
NOTE 2 Mass emission rates related to the sampling duration of the mass concentration measurement are called
“short-term averages” in the following.
NOTE 3 When, in the course of periodic or manual measurement, a series of tests has been made under similar
process operating conditions, as specified in the measurement plan, the results can be averaged and the result can be
taken to be representative of the time period of the measurement sequence as a whole.
When using automated continuous measurement, the mass emission rate shall be generated continuously
and recorded as a time series of fixed period averages. The time series may be averaged and the result taken
to be representative of the time period of the measurement sequence as a whole.
NOTE 4 For most processes, hourly or half hourly averaging is suitable.
6 © ISO 2010 – All rights reserved

ISO 11771:2010(E)
5.4 Determination of time-averaged mass emission rates
Average the mass emission rates over the averaging period specified in the measurement plan.
NOTE 1 Mass emission rates averaged over the averaging period specified in the measurement plan are called “long-
term averages” in the following.
When using periodic or manual measurement, a number of tests may be averaged over a longer time period
provided that they conform to 5.2 and the uncertainty criteria as specified in the measurement plan are met.
When using an automated continuous measurement system, the time-averaged mass emission rate is the
simple arithmetic average of the time resolved mass emission rates (e.g. half hourly) for the periods when the
process was within the operational criteria specified in the measurement plan.
Record the installation process conditions for which the derived value is applicable and document the
proportion of time during the averaging period for which the installation was operating outside the criteria
specified in the measurement plan (see 5.1.2 and Annex A).
Record the derived value of the averaged mass emission rate in SI units. The value may, in addition to SI
units, be reported in superseded units, provided it is made clear that the superseded units are given for
information only.
NOTE 2 The mass emission rate data can be obtained by continuous or intermittent monitoring by means of a specified
measuring system. The uncertainty of the time average depends on both the uncertainty of the measurement results and
[4]
the uncertainty due to incomplete time coverage of the data set arising from missing data. ISO 11222 can be used to
calculate the additional uncertainty, due to incomplete time coverage, of the mean value of a mass emission rate obtained
[4]
from a series of measurements. ISO 11222 is applicable only when the time series data used are representative of the
temporal structure of the emission as a whole.
5.5 Uncertainty estimation
5.5.1 General
The uncertainty of the mass emission rate of a measured component shall be determined in accordance with
[10]
the general principles of ISO/IEC Guide 98-3:2008 .
The determination of the uncertainty of short-term averages of the mass emission rate requires:
⎯ establishment of a suitable model equation describing the whole measurement process and the
relationship between the input quantities used to calculate the mass emission rate;
⎯ determination of the variance equation describing the combination of the uncertainty contributions of the
individual input quantities by application of the law of uncertainty propagation to the model equation;
⎯ determination of the uncertainty of the input quantities;
⎯ calculation of the standard uncertainty of the mass emission rate;
⎯ determination of a coverage factor taking into account the number of degrees of freedom associated with
the individual uncertainty contributions and the level of confidence;
⎯ calculation of the expanded uncertainty of the mass emission rate.
The standard uncertainty and the associated number of degrees of freedom shall be available for the
measured input quantities used to calculate the mass emission rate by use of the model equation. Suitable
standard measurement methods for the input quantities have known uncertainties, which are often expressed
as repeatability and reproducibility in the field. If the mass emission rate is calculated from data collected
using non-standard methods, this information is often missing. The user shall determine the uncertainty of the
measurement methods used to measure the input quantities and shall verify the uncertainty by comparison
[9]
with documented values obtained e.g. during the validation of the measurement method. ISO 20988
ISO 11771:2010(E)
provides guidance on the estimation of the uncertainty of air quality measurements, such as concentration and
volume flow measurements, and the associated number of degrees of freedom.
The estimation of the uncertainty of long-term averages of the mass emission rate shall be based on a model
equation, which includes the measurement induced uncertainty of the short-term averages and the additional
[4]
uncertainty due to incomplete coverage of the time period of the long-term average. ISO 11222 provides
guidance on the determination of the uncertainty of time averages of air quality measurements.
The model equation should address the time period of the long-term average, particularly with respect to the
calibration frequency of emission measuring equipment. For example, if continuous monitoring equipment is
[11]
calibrated following EN 14181 , then calibration is carried out with up to a 3 year time period, with annual
calibration checks, against a standard reference method. This calibration regime leads to a number of
uncertainty sources which can be considered systematic over a yearly emissions reporting period.
5.5.2 Standard uncertainty
The standard uncertainty of short-term averages of the mass emission rate of a measured component shall be
calculated as the square root of the variance of the mass emission rate, which is given as the sum of the
variance contributions of the individual input quantities.
The standard uncertainty of long-term averages of the mass emission rate of a measured component shall
include the measurement-induced uncertainty and the uncertainty due to incomplete coverage of the
averaging period of the emission rate data.
NOTE 1 The mass emission rate data can be obtained by continuous or intermittent monitoring by means of a specified
measuring system. The uncertainty of the time average depends on both the uncertainty of the measurement results and
the uncertainty due to incomplete time coverage of the data set arising from missing data.
The random and systematic uncertainty components of the short-term averages have to be taken into account
[4]
when calculating the measurement-induced uncertainty of long-term averages (see e.g. ISO 11222 ).
NOTE 2 The uncertainty of the long-term average can not be calculated by summing the uncertainties of shorter time
periods divided by the square root of the number of these shorter time periods as this requires completely random
uncertainties.
NOTE 3 The uncertainty estimation for the long-term average requires the establishment of a model equation, which
allows the correct handling of random and systematic uncertainties.
For a time series of short-term averages of measured mass emission rates, the measurement induced
uncertainty of the long-term average may be taken to be the same as the uncertainty of the individual mass
emissions rates. This is equivalent to assuming that all uncertainty sources are systematic, which provides a
safe estimate of the measurement-induced uncertainty of the long-term average.
NOTE 4 The assumption that all uncertainties are systematic can be considered as a worst case scenario.
[4]
ISO 11222 can be used to calculate the additional uncertainty, due to incomplete time coverage, of the
average of a mass emission rate obtained from a series of measurements.
5.5.3 Expanded uncertainty
The expanded uncertainty of the mass emission rate, which is the dispersion of the range of values that could
reasonably be expe
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