ISO 22241-1

• Abstract:

  This document specifies the quality characteristics of the NOx reduction agent AUS 32 (aqueous urea solution) which is needed to operate selective catalytic reduction (SCR) converter systems in motor vehicles with diesel engines. SCR converter systems are particularly suitable for selectively reducing the nitrogen oxide (NOx) emissions of diesel engines.

• Status: Not Published
• ICS: 43.060.40 - Fuel systems
• Technical Committee: ISO/TC 22/SC 34 - Propulsion, powertrain and powertrain fluids
• Drafting Committee: ISO/TC 22/SC 34/WG 14 - NOx reduction additive
• Current Stage: 6000 - International Standard under publication
• Start Date: 24-Sep-2026
• Completion Date: 26-Sep-2026

• Revises: ISO 22241-1:2019/Amd 1:2019 - Diesel engines — NOx reduction agent AUS 32 — Part 1: Quality requirements — Amendment 1
• Effective Date: 07-Jan-2025
• Revises: ISO 22241-1:2019 - Diesel engines — NOx reduction agent AUS 32 — Part 1: Quality requirements
• Effective Date: 07-Jan-2025

Overview

ISO 22241-1 is the core quality requirements standard for diesel engine NOx reduction agent AUS 32, also known as aqueous urea solution or diesel exhaust fluid (DEF). It defines the quality characteristics needed to operate selective catalytic reduction (SCR) converter systems in motor vehicles with diesel engines.

This ISO standard is important for supporting diesel emissions control, helping ensure that AUS 32 performs reliably in SCR systems designed to reduce nitrogen oxide (NOx) emissions. The document is part of the ISO 22241 series, which also covers test methods, handling, transportation, storage, and refilling interface requirements.

ISO 22241-1 is widely relevant to:

• Vehicle and engine manufacturers
• SCR converter manufacturers
• AUS 32 producers and distributors
• Fleet operators
• Quality and compliance teams in the automotive supply chain

Key Topics

Quality requirements for AUS 32

The standard specifies the quality characteristics of AUS 32 and requires conformance to defined limits for key properties. These include:

• Urea content
• Refractive index
• Alkalinity
• Biuret
• Aldehydes
• Insoluble matter
• Phosphate
• Selected metal contaminants

These requirements help maintain product consistency and support dependable SCR operation.

Testing and verification

ISO 22241-1 requires that quality characteristics be verified using the referenced test methods, with ISO 22241-2 serving as the primary source for test methods. In case of dispute, the methods listed in the standard are the referee methods.

Handling and marking

The standard also references the need for proper handling, transportation, and storage in the supply chain. Retail distribution pumps and containers must be marked with the correct designation, such as AUS 32 ISO 22241-1 or a regional equivalent like DEF ISO 22241-1.

Technical consistency

The document helps ensure that commercially available AUS 32 products remain suitable for SCR systems and do not impair performance. It supports stable product quality from production through vehicle use.

Applications

ISO 22241-1 is used in practical diesel emissions management across the automotive sector. Typical applications include:

• Diesel vehicles equipped with SCR systems
• Quality control of AUS 32 production
• Fuel and fluid logistics for emissions-related consumables
• Procurement and supplier qualification
• Fleet maintenance and refilling operations

For organizations involved in diesel exhaust fluid quality assurance, the standard provides a common basis for product specification, testing, and labeling. This is especially valuable where consistent NOx reduction agent performance is needed across large vehicle fleets or international supply chains.

Related Standards

The following standards and documents are closely connected to ISO 22241-1:

• ISO 22241-2 - Test methods for AUS 32
• ISO 22241-3 - Handling, transportation, and storage
• ISO 22241 (all parts) - Complete series for diesel engines NOx reduction agent AUS 32
• ISO 3696 - Water for analytical laboratory use
• IATF 16949:2016 - Quality management systems for automotive production
• ISO 4259 series - Precision of measurement methods and results

Together, these documents form a practical framework for AUS 32 quality management, SCR emissions control, and diesel engine emissions compliance.

FINAL DRAFT
International
Standard
ISO/FDIS 22241-1
ISO/TC 22/SC 34
Diesel engines — NOx reduction
Secretariat: JISC
agent AUS 32 —
Voting begins on:
2026-07-29
Part 1:
Quality requirements
Voting terminates on:
2026-09-23
Moteurs diesel — Agent AUS 32 de réduction des NOx —
Partie 1: Exigences de qualité
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 22241-1:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 22241-1:2026(en)
International
Standard
ISO/FDIS 22241-1
ISO/TC 22/SC 34
Diesel engines — NOx reduction
Secretariat: JISC
agent AUS 32 —
Voting begins on:
Part 1:
Quality requirements
Voting terminates on:
Moteurs diesel — Agent AUS 32 de réduction des NOx —
Partie 1: Exigences de qualité
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 22241-1:2026(en) © ISO 2026

ii
ISO/FDIS 22241-1:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Designation . 2
5 Requirements and testing . 2
6 Handling, transportation and storage. 3
7 Marking . . 3
Annex A (informative) Chemical characteristics . 4
Annex B (informative) Precision of test methods . 5
Bibliography . 6

iii
ISO/FDIS 22241-1:2026(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention drawn to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This third edition cancels and replaces the second edition (ISO 22241-1:2019), which has been technically
revised. It also incorporates the Amendment ISO 22241-1:2019/Amd 1:2019.
The main changes are as follows:
— incorporation of the ISO 22241-1:2019/Amd 1:2019 and editorial updates;
— alternative test method for biuret in Table 1 announced.
A list of all parts in the ISO 22241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/FDIS 22241-1:2026(en)
Introduction
In order to protect the environment, keeping the air quality as clean as possible, exhaust emissions
regulations around the world have been strengthened considerably. In motor vehicles with diesel engines,
particulate matters (PM) and nitrogen oxide (NOx) emissions are the main concern, and efforts have
been focused on the development of technology which can reduce them effectively with minimum fuel
economy penalty. Selective catalytic reduction (SCR) converters using aqueous urea solution (AUS 32)
as the reduction agent are considered to be a key technology for reducing NOx emissions. The quality of
the urea solution used for that technology needs to be specified to ensure reliable and stable operation of
[1]
the SCR converter systems. ISO 22241 (all parts) provides the specifications for quality characteristics,
handling, transportation and storage, and refilling interface. It also outlines the test methods needed by the
manufacturers of motor vehicles and their engines, converter manufacturers, producers and distributors of
the urea solution, as well as fleet operators.
The aqueous urea solution (AUS 32), as specified in this document, is commercially available and may exist
1)
under various trade names, as for example AdBlue®, ARLA 32 .
1) Trade names of products AdBlue®, ARLA 32, DEF, etc., are examples of suitable products available commercially. This
information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the
products named.
v
FINAL DRAFT International Standard ISO/FDIS 22241-1:2026(en)
Diesel engines — NOx reduction agent AUS 32 —
Part 1:
Quality requirements
1 Scope
This document specifies the quality characteristics of the nitrogen oxide (NOx) reduction agent aqueous
urea solution (AUS 32), which is needed to operate selective catalytic reduction (SCR) converter systems in
motor vehicles with diesel engines. SCR converter systems are particularly suitable for selectively reduci
...

ISO/FDIS 22241-1
ISO/TC 22/SC 34
Secretariat: JISC
Diesel engines — NOx reduction agent AUS 32 —
Part 1:
Quality requirements
Moteurs diesel — Agent AUS 32 de réduction des NOx —
Partie 1: Exigences de qualité
FDIS stage
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ISO/DISFDIS 22241-1:2026(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/DISFDIS 22241-1:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Designation . 2
5 Requirements and testing. 2
6 Handling, transportation and storage . 3
7 Marking . 3
Annex A (informative) Chemical characteristics . 5
Annex B (informative) Precision of test methods . 6
Bibliography . 7

iii
ISO/DISFDIS 22241-1:2026(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention drawn to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rihgtsrights in respect thereof. As of the date of publication of this document, ISO had not received notice of
(a) patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This third edition cancels and replaces the second edition (ISO 22241-1:2019), which has been technically
revised. It also incorporates the Amendment ISO 22241-1:2019/Amd 1:2019.
The main changes compared to the previous edition are as follows:
— incoorperationincorporation of the ISO 22241-1:2019/Amd 1:2019 and editorial updates;
— alternative test method for buiretbiuret in Table 1 announced;
— editorially revised.
A list of all parts in the ISO 22241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
ISO/DISFDIS 22241-1:2026(en)
Introduction
In order to protect the environment, keeping the air quality as clean as possible, exhaust emissions regulations
around the world have been strengthened considerably. In motor vehicles with diesel engines, particulate
matters (PM) and nitrogen oxide (NOx) emissions are the main concern, and efforts have been focused on the
development of technology which can reduce them effectively with minimum fuel economy penalty. Selective
catalytic reduction (SCR) converters using aqueous urea solution (AUS 32) as the reduction agent are
considered to be a key technology for reducing NOx emissions. The quality of the urea solution used for that
technology needs to be specified to ensure reliable and stable operation of the SCR converter systems. ISO
22241 (all parts)The ISO 22241 series provides the specifications for quality characteristics, handling,
transportation and storage, and refilling interface. It also outlines the test methods needed by the
manufacturers of motor vehicles and their engines, converter manufacturers, producers and distributors of
the urea solution, as well as fleet operators.
The aqueous urea solution (AUS 32), as specified in this document, is commercially available and may exist
1)
under various trade names, as for example AdBlue®, ARLA 32 .

1)
Trade names of products AdBlue®, ARLA 32, DEF, etc., are examples of suitable products available commercially as
AUS 32. This information is given for the convenience of users of this document and does not constitute an endorsement
by ISO of the products named.
v
ISO/FDIS 22241-1:2026(en)
Diesel engines — NOx reduction agent AUS 32 —
Part 1:
Quality requirements
1 Scope
This document specifies the quality characteristics of the nitrogen oxide (NOx) reduction agent aqueous urea
solution (AUS 32), which is needed to operate selective catalytic reduction (SCR) converter systems in motor
vehicles with diesel engines. SCR converter systems are particularly suitable for selectively reducing the NOx
emissions of diesel engines.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 22241-2:2019, Diesel engines — NOx reduction agent AUS 32 — Part 2: Test methods
ISO 22241-2, Diesel engines — NOx reduction agent AUS 32 — Part 2: Test methods
ISO 22241-3, Diesel engines — NOx reduction agent AUS 32 — Part 3: Handling, transportation, and storage
3 Terms and definitions
For the purposes of this document, the following terms and definitions app
...