prEN ISO 16890-1

SLOVENSKI STANDARD
01-julij-2025
Zračni filtri pri splošnem prezračevanju - 1. del: Tehnične specifikacije, zahteve in
klasifikacijski sistem učinkovitosti na podlagi drobnih delcev (ePM) (ISO/DIS 16890
-1:2025)
Air filters for general ventilation - Part 1: Technical specifications, requirements and
classification system based upon particulate matter efficiency (ePM) (ISO/DIS 16890-
1:2025)
Luftfilter für die allgemeine Raumlufttechnik - Teil 1: Technische Bestimmungen,
Anforderungen und Effizienzklassifizierungssystem, basierend auf dem
Feinstaubabscheidegrad (ePM) (ISO/DIS 16890-1:2025)
Filtres à air de ventilation générale - Partie 1: Spécifications techniques, exigences et
système de classification fondé sur l'efficacité des particules en suspension (ePM)
(ISO/DIS 16890-1:2025)
Ta slovenski standard je istoveten z: prEN ISO 16890-1
ICS:
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 16890-1
ISO/TC 142
Air filters for general ventilation —
Secretariat: UNI
Part 1:
Voting begins on:
Technical specifications, 2025-04-30
requirements and classification
Voting terminates on:
2025-07-23
system based upon particulate
matter efficiency (ePM)
Filtres à air de ventilation générale —
Partie 1: Spécifications techniques, exigences et système de
classification fondé sur l'efficacité des particules en suspension
(ePM)
ICS: 91.140.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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Reference number
ISO/DIS 16890-1:2025(en)
DRAFT
ISO/DIS 16890-1:2025(en)
International
Standard
ISO/DIS 16890-1
ISO/TC 142
Air filters for general ventilation —
Secretariat: UNI
Part 1:
Voting begins on:
Technical specifications,
requirements and classification
Voting terminates on:
system based upon particulate
matter efficiency (ePM)
Filtres à air de ventilation générale —
Partie 1: Spécifications techniques, exigences et système
de classification fondé sur l'efficacité des particules en
suspension (ePM)
ICS: 91.140.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 16890-1:2025(en)
ii
ISO/DIS 16890-1:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 5
5 Technical specifications and requirements . 5
5.1 General .5
5.2 Material .6
5.3 Nominal air flow rate .6
5.4 Resistance to air flow .6
5.5 Fractional efficiency curves (particle size efficiency spectrum) .6
5.6 Arrestance .6
6 Test methods and procedure . 6
7 Classification system based on particulate matter efficiency (ePM) . 7
7.1 Definition of a standardized particles size distribution of ambient air .7
7.2 Calculation of the particulate matter efficiencies (ePM) .9
7.3 Classification .10
8 Reporting . 10
8.1 General .10
8.2 Interpretation of test reports .11
8.3 Summary .11
Annex A (informative) Shedding from filters . 17
Annex B (informative) Examples . 19
Annex C (informative) Estimation of downstream fine dust concentrations .23
Annex D (informative) Filtration efficiency against biological aerosols .26
Bibliography .27

iii
ISO/DIS 16890-1:2025(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 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 of 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 142, Cleaning equipment for air and other gases,
in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
195, Cleaning equipment for air and other gases, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 16890-1:2016), which has been technically
revised.
The main changes are as follows:
— correction of Formula 2 and 3 in Section 7.1;
— addition of Annex D Filtration efficiency against biological aerosols;
— a list of all parts in the ISO 16890 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/DIS 16890-1:2025(en)
Introduction
The effects of particulate matter (PM) on human health have been extensively studied in the past decades.
The results are that fine dust can be a serious health hazard, contributing to or even causing respiratory
and cardiovascular diseases. For the outdoor environment, the U.S. Environmental Protection Agency (EPA),
the World Health Organization (WHO), the European Union, and other national agencies have established
acceptable air quality standards according to concentrations of particulate matter classified per their
aerodynamic sizes, defined as PM2,5 and PM10, and measured according to strict prescriptive methods and
sampling times.
Since there is growing interest in relating indoor air quality to outdoors, ISO 16890 series of standards
classifies ventilation filters according to their efficiencies measured with an optical diameter between
0,3 µm and x µm and relating the result to historic global average ambient PM concentrations. Although not
exactly equivalent to filter performance at national ambient air quality standards at PM, the classification
scheme presented in the standards will yield a level correspondence to the effectiveness of the filter for
ambient particle concentrations. It is however recognized that the correspondence based on global averages
may not be exactly the same at a specific location since local ambient particle concentration may be different
than the global average.
The particle size ranges described in Table 1 are used in the ISO 16890 series for the listed efficiency values
and noted as ePM .
x
Table 1 — Optical particle diameter size ranges for the definition of the efficiencies, ePM
x
Efficiency Size range, µm
ePM 0,3 ≤ × ≤10
ePM 0,3 ≤ × ≤2,5
2,5
ePM 0,3 ≤ × ≤1
Air filters for general ventilation are widely used in heating, ventilation and air-conditioning applications
of buildings. In this application, air filters significantly influence the indoor air quality and, hence, the
health of people, by reducing the concentration of particulate matter. To enable design engineers and
maintenance personnel to choose the correct filter types, there is an interest from international trade and
manufacturing for a well-defined, common method of testing and classifying air filters according to their
particle efficiencies, especially with respect to the removal of particulate matter. Current regional standards
are applying totally different testing and classification methods, which do not allow any comparison
with each other, and thus hinder global trade with common products. Additionally, the current industry
standards have known limitations by generating results which often are far away from filter performance
in service, i.e. overstating the particle removal efficiency of many products. With this new ISO 16890 series,
a completely new approach for a classification system is adopted, which gives better and more meaningful
results compared to the existing standards.
The ISO 16890 series describes the equipment, materials, technical specifications, requirements, qualifications
and procedures to produce the laboratory performance data and efficiency classification based upon the
measured fractional efficiency converted into a particulate matter efficiency (ePM) reporting system.
Air filter elements according to the ISO 16890 series are evaluated in the laboratory by their ability to
remove aerosol particulate expressed as the efficiency values ePM , ePM and ePM . The air filter elements
1 2,5 10
can then be classified according to the procedures defined in this part of ISO 16890. The particulate removal
efficiency of the filter element is measured as a function of the particle size in the range of 0,3 µm to 10 µm
of the unloaded and unconditioned filter element as per the procedures defined in ISO 16890-2. After the
initial particulate removal efficiency testing, the air filter element is conditioned according to the procedures
defined in ISO 16890-4 and the particulate removal efficiency is repeated on the conditioned filter element.
This is done to provide information about the intensity of any electrostatic removal mechanism which may
or may not be present with the filter element for test. The average efficiency of the filter is determined by
calculating the mean between the initial efficiency and the conditioned efficiency for each size range. The
average efficiency is used to calculate the ePM efficiencies by weighting these values to the standardized and
x
normalized particle size distribution of the related ambient aerosol fraction. When comparing filters tested

v
ISO/DIS 16890-1:2025(en)
in accordance with the ISO 16890 series, the fractional efficiency values shall always be compared among
the same ePM class (ex. ePM of filter A with ePM of filter B). The test dust capacity and the arrestance of
x 1 1
a filter element are determined as per the test procedures defined in ISO 16890-3. The performance results
obtained in accordance with ISO 16890 series cannot by themselves be quantitatively applied to predict
performance in service with regard to efficiency and lifetime. Other factors influencing performance to be
taken into account are described in Annex A.

vi
DRAFT International Standard ISO/DIS 16890-1:2025(en)
Air filters for general ventilation —
Part 1:
Technical specifications, requirements and classification
system based upon particulate matter efficiency (ePM)
1 Scope
This document specifies an efficiency classification system of air filters for general ventilation based
upon particulate matter (PM). It also provides an overview of the test procedures, and specifies general
requirements for assessing and marking the filters, as well as for documenting the test results. It is intended
for use in conjunction with ISO 16890-2, ISO 16890-3 and ISO 16890-4.
The test method described in this part of ISO 16890 is applicable for air flow rates between 0,25 m /s
3 3 3 3 3
(900 m /h, 530 ft /min) and 1,5 m /s (5 400 m /h, 3 178 ft /min), referring to a test rig with a nominal face
area of 610 mm × 610 mm (24 inch × 24 inch).
This document refers to particulate air filter elements for general ventilation having an ePM efficiency less
than or equal to 99 % and an ePM efficiency greater than 20 % when tested as per the procedures defined
in the ISO 16890 series.
NOTE The lower limit for this test procedure is set at a minimum ePM efficiency of 20 % since it is very difficult
for a test filter element below this level to meet the statistical validity requirements of this procedure.
This document does not apply to filter elements used in portable room-air cleaners.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 15957, Test dusts for evaluating air cleaning equipment
ISO 16890-2:2022, Air filters for general ventilation — Part 2: Measurement of fractional efficiency and air flow
resistance
ISO 16890-3:2024, Air filters for general ventilation — Part 3: Determination of the gravimetric efficiency and
the air flow resistance versus the mass of test dust captured
ISO 16890-4:2022, Air filters for general ventilation — Part 4: Conditioning method to determine the minimum
fractional test efficiency
ISO 29464:2024, Cleaning of air and other gases — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 29464 and the following apply.
3.1 Air flow and resistance
ISO/DIS 16890-1:2025(en)
3.1.1
air flow rate
volume of air flowing through an air cleaner per unit time
[SOURCE: ISO 29464:2024, 3.1.29, modified — The preferred term "flow rate" has been removed.]
3.1.2
nominal air flow rate
air flow rate (3.1.1) specified by the manufacturer
3.1.3
test air flow rate
air flow rate (3.1.1) used for testing
3.1.4
resistance to air flow
difference in absolute (static) pressure between two points in an air flow system at specified conditions,
especially when measured across the filter element (3.2.2)
Note 1 to entry: Resistance to air flow is measured in Pa (inches of water).
[SOURCE: ISO 29464:2024, 3.1.43, modified — The admitted terms have been removed; “at specified
conditions, especially when measured across the filter element” has been added.]
3.1.5
final resistance to air flow
resistance to air flow (3.1.2) up to which the filtration performance is measured to determine the test dust
capacity (3.3.4)
Note 1 to entry: Final resistance to air flow is measured in Pa (inches of water).
[SOURCE: ISO 29464:2024, 3.2.142, modified – “for classification or other purposes” has been replaced with
“to determine the test dust capacity”.]
3.2 Test Device
3.2.1
test device
air cleaner that is being subjected to performance testing
[SOURCE: ISO 29464:2024, 3.1.45, modified — The preferred terms "device under test" and "DUT" have been
removed.]
3.2.2
filter element
structure made of the filtering material, its supports and its interfaces with the filter housing
[SOURCE: ISO 29464:2024, 3.2.59]
3.2.3
upstream
U/S
area or region from which fluid flows as it enters an air cleaner
[SOURCE: ISO 29464:2024, 3.1.46, modified — "U/S" has been added as an admitted term.]
3.2.4
downstream
D/S
area or region into which fluid flows on leaving an air cleaner
[SOURCE: ISO 29464:2024, 3.1.16, modified — "D/S" has been added as an admitted term.]

ISO/DIS 16890-1:2025(en)
3.3 Arrestance and efficiency
3.3.1
arrestance
measure of the ability of a filter to remove a standard test dust from the air passing through it under given
operating conditions
Note 1 to entry: This measure is expressed as a mass fraction.
[SOURCE: ISO 29464:2024, 3.2.15, modified — The preferred term "gravimetric arrestance" has been
removed; "mass percentage" has been replaced by "mass fraction" in note 1 to entry.]
3.3.2
initial arrestance
ratio of the mass of a standard test dust retained by the filter to the mass of dust fed after the first increment
of dust load
Note 1 to entry: This measure is expressed as a mass fraction.
Note 2 to entry: For example, see the procedure in ISO 29461-1 or this document.
[SOURCE: ISO 29464:2024, 3.2.17, modified — The preferred term "initial gravimetric arrestance" has
been removed; "mass percentage" has been replaced by "mass fraction" in note 1 to entry; the reference to
"ISO 16890-3" has been replaced by "this document" in note 2 to entry.]
3.3.4
efficiency
fraction or percentage of a challenge contaminant that is removed by a filter
3.3.5
fractional efficiency
ability of an air cleaning device to remove particles of a specific size or size range
Note 1 to entry: The efficiency plotted as a function of particle size (3.7.1) gives the particle size efficiency spectrum.
[SOURCE: ISO 29464:2024, 3.2.135, modified – the preferred term “fractional removal Efficiency” has been
replaced by “fractional efficiency”.]
3.3.6
particulate matter efficiency
ePM
x
efficiency (3.1.4) of an air cleaning device to reduce the mass concentration of particles with an optical
diameter between 0,3 µm and x µm
3.4 Particulate matter
3.4.1
particulate matter
PM
solid and/or liquid particles
[SOURCE: ISO 29464:2024, 3.2.123]
3.5.2
particulate matter PM
particulate matter (3.5.1) which passes through a size-selective inlet with a 50 % efficiency cut-off at 10 μm
aerodynamic diameter
[SOURCE: ISO 29464:2024, 3.2.125]

ISO/DIS 16890-1:2025(en)
3.5.3
particulate matter PM
2,5
particulate matter (3.5.1) which passes through a size-selective inlet with a 50 % efficiency cut-off at 2,5 μm
aerodynamic diameter
[SOURCE: ISO 29464:2024, 3.2.126]
3.5.4
particulate matter PM
particulate matter (3.5.1) which passes through a size-selective inlet with a 50 % efficiency cut-off at 1 μm
aerodynamic diameter
[SOURCE: ISO 29464:2024, 3.2.127]
3.5.5
group designation
designation of a group of filters fulfilling certain requirements in the filter classification
Note 1 to entry: This document defines four groups of filters. Group designations are “ISO coarse”, “ISO ePM10”, “ISO
ePM2,5” and “ISO ePM1” as defined in Table 4.
3.7 Particle size and test dust capacity
3.7.1
particle counter
device for detecting and counting numbers of discrete airborne particles present in a sample of air
[SOURCE: ISO 29464:2024, 3.2.96]
3.7.2
particle size
particle diameter
geometric diameter (equivalent spherical, optical or aerodynamic, depending on context) of the particles of
an aerosol
[SOURCE: ISO 29464:2024, 3.2.116]
3.7.3
particle size distribution
presentation, in the form of tables of numbers or of graphs, of the experimental results obtained using a
method or an apparatus capable of measuring the equivalent diameter of particles in a sample or capable of
giving the proportion of particles for which the equivalent diameter lies between defined limits
[SOURCE: ISO 29464:2024, 3.2.118]
3.7.4
test dust capacity
TDC
total mass of loading dust (3.7.5) captured by an air-cleaning device up to the final test resistance to air flow (3.1.5)
[SOURCE: ISO 29464:2024, 3.2.23, modified — The preferred terms "dust holding capacity" and "DHC" and
the admitted term "dust loading capacity" have been removed.]
3.7.5
loading dust
synthetic dust formulated specifically for determination of the test dust capacity (3.7.4) and arrestance
(3.3.1) of air filters
[SOURCE: ISO 29464:2024, 3.2.45, modified — The preferred term "synthetic test dust" has been removed.]

ISO/DIS 16890-1:2025(en)
4 Symbols and abbreviated terms
A initial arrestance, %
i
d lower limit particle diameter in a size range i, µm
i
d upper limit particle diameter in a size range i, µm
i+1
geometric mean diameter of a size range i, µm
d
i
Δd width of a particle diameter size range i, µm
i
Δln d logarithmic width of a particle diameter size range, i; ln is the natural logarithm to the
i
base of e, where e is an irrational and transcendental constant approximately equal to
2,718 281 828
Δlndd=−ln lndd=ln /d , dimensionless
()
ii++11ii i
d median particle size of the log-normal distribution, µm
E initial fractional efficiency of particle size range, i, of the untreated and unloaded filter
i
element, % (equals to the efficiency values E of the untreated filter element resulting from
ps
ISO 16890-2)
E fractional efficiency of particle size range, i, of the filter element after an artificial
D,i
conditioning step, % (equals to the efficiency values E of the filter element resulting
ps
from ISO 16890-2 after a conditioning step has been carried out according to
ISO 16890-4)
E average fractional efficiency of particle size range i, %
A,i
ePM minimum efficiency value with x=1 µm, 2,5 µm or 10 µm of the conditioned filter element, %
x, min
ePM efficiency with x=1 µm, 2,5 µm or 10 µm, %
x
q air flow rate at filter, m /s
V
q nominal air flow rate from manufacturer, m /s
V,nom
q test air flow rate at filter, m /s
Vt
q (d) discrete particle volume distribution, dimensionless
Q (d) cumulative particle volume distribution, dimensionless
σ standard deviation of the log-normal distribution
g
y mixing ratio of the bimodal particle size distribution
ASHRAE American Society of Heating Refrigeration and Air Conditioning Engineers
CEN European Committee for Standardization
5 Technical specifications and requirements
5.1 General
The filter element shall be designed or marked for air flow direction in a way that prevents incorrect
mounting.
ISO/DIS 16890-1:2025(en)
The filter shall be designed in a way that no leaks occur along the sealing edge when correctly mounted
in the ventilation duct. If, for any reason, dimensions do not allow testing of a filter under standard test
conditions, assembly of two or more filters of the same type or model are permitted, provided no leaks occur
in the resulting filter configuration.
5.2 Material
The filter element shall be made of suitable material to withstand normal usage and exposures to those
temperatures, humidities and corrosive environments that are likely to be encountered.
The filter element shall be designed to withstand mechanical constraints that are likely to occur during
normal use.
5.3 Nominal air flow rate
The filter element shall be tested at its nominal air flow rate for which the filter has been designed by the
manufacturer.
3 3 3
However, many national and association bodies use 0,944 m /s (2 000 ft /min or 3 400 m /h) as nominal
air flow for classification or rating of air filters that are nominal 610 mm × 610 mm (24 inch × 24 inch) in
face area. Therefore, if the manufacturer does not specify a nominal air flow rate, the filter shall be tested at
0,944 m /s. The air flow velocity associated with this air flow rate is 2,54 m/s (500 ft/min).
5.4 Resistance to air flow
The resistance to air flow across the filter element is recorded at the test air flow rate as described in detail
in ISO 16890-2.
5.5 Fractional efficiency curves (particle size efficiency spectrum)
The initial fractional efficiency curve, E , of the unloaded and unconditioned filter element as a function of
i
the particle size is measured at the test air flow rate in accordance with ISO 16890-2.
The fractional efficiency curve, E , of the filter element after an artificial conditioning step defined in
D,i
ISO 16890-4 is determined as a function of the particle size in accordance with ISO 16890-2.
5.6 Arrestance
The initial arrestance, the resistance to air flow versus the mass of test dust captured and the test dust
capacity are determined in accordance with ISO 16890-3 using L2 test dust as specified in ISO 15957.
6 Test methods and procedure
The technical specifications of the test rig(s), the related test conditions, test aerosols and standard test dust
used in this document are described in detail in ISO 16890-2, ISO 16890-3 and ISO 16890-4. The full test
according to this document consists of the steps given below, which all shall be carried out with the same
filter test specimen under the same test conditions and at the same test air flow rate:
a) measure the resistance to air flow as a function of the air flow rate according to ISO 16890-2;
b) measure the initial fractional efficiency curve, E , of the unloaded and unconditioned filter element as a
i
function of the particle size in accordance with ISO 16890-2;
c) carry out an artificial conditioning step in accordance with ISO 16890-4;
d) measure the fractional efficiency curve, E , of the conditioned filter element as a function of the particle
D,i
size in accordance with ISO 16890-2, which is equal to the minimum fractional test efficiency;
e) calculate the ePM efficiencies as defined in Clause 7;

ISO/DIS 16890-1:2025(en)
f) load the filter with synthetic L2 test dust as specified in ISO 15957 according to the procedures
described in ISO 16890-3 to determine the initial arrestance, the resistance to air flow versus the mass
of test dust captured and the test dust capacity (this step is optional for filters of group ISO ePM10,
ePM2,5 or ePM1).
The initial fractional efficiency curve, E , of the untreated and unloaded filter element (see 5.5) and the
i
fractional efficiency curves, E , after an artificial conditioning step are used to calculate the average
D,i
fractional efficiency curve, E , using Formula (1).
A,i
EE=⋅05, +E (1)
()
AD,,ii i
NOTE For further explanations on the test procedure according to ISO 16890-4, please refer to 8.2.
The procedure described in ISO 16890-4 quantitatively shows the extent of the electrostatic charge effect on
the initial performance of the filter element without dust load. It indicates the level of efficiency obtainable
with the charge effect completely removed and with no compensating increase in mechanical efficiency.
Hence, the fractional efficiencies, E , after an artificial conditioning step could underestimate the fractional
D,i
efficiencies under real service conditions. Since the real minimum fractional efficiencies encountered during
service strongly depend on the operating conditions defined by numerous uncontrolled parameters, its
real value lays unpredictably between the initial and the conditioned value. For good sense, in this part of
ISO 16890, the average between the initial and the conditioned value is used to predict the real fractional
efficiencies of a filter during service, as defined by Formula (1). Therefore, it shall be noted that fractional
efficiencies measured in real service may differ significantly from the ones given in this part of ISO 16890.
Additionally, the chemical treatment of a filter medium applied in ISO 16890-4 as an artificial ageing step
may affect the structure of the fibre matrix of a filter medium or chemically affect the fibres or even fully
destroy the filter medium. Hence, not all types of filters and media may be applicable to the mandatory
procedure described in ISO 16890-4 and, in this case, cannot be classified according to this part of ISO 16890.
7 Classification system based on particulate matter efficiency (ePM)
7.1 Definition of a standardized particles size distribution of ambient air
To evaluate air filters according to their ePM efficiencies, standardized volume distribution functions of the
particle size are used which globally represent the average ambient air of urban and rural areas, respectively.
Typically, in the size range of interest (>0,3 µm), the particle sizes in ambient air are bimodal distributed with
a fine and coarse mode. Fine filters, mostly designed to filter out the PM and PM particle size fractions,
1 2,5
are evaluated using a size distribution which represents urban areas, while fine filters predominantly
designed to filter out the PM fraction are evaluated using a size distribution which represents rural areas.
NOTE The actual particle size distribution of ambient air depends on many different factors. Hence, depending
on the location, the season of the year and the weather conditions, the actual measured particle size distribution may
differ significantly from the standardized one given in this part of ISO 16890.
This bimodal distribution is represented by combining lognormal distributions for the coarse and the fine
mode as given in Formula (3).
 2 
lndd−ln
1 ()
 
fd,,σ d = ⋅−exp (2)
()
g 50
 
lnσπ⋅ 2
g 2⋅ lnσ
()
g
 
In Formula (2), fd,,σ d represents the lognormal distribution function for one mode, coarse or fine,
()
g 50
where d is the variable particle size, for which the distribution is calculated, and the standard deviation, σ ,
g
and the median particle size, d , are the scaling parameters. The bimodal distribution is derived as given in
ISO/DIS 16890-1:2025(en)
Formula (3) by combining the lognormal distributions for the coarse (B) and the fine (A) mode, weighted
with the mixing ratio, y.
dQd()
qd()== yf⋅ dd,,σσ+−()1 yf⋅ dd,, (3)
() ()
3 gA 50AgBB50
dlnd
where the parameters are defined to the values given in Table 2, representing urban and rural areas.
Table 2 — Parameters for the distribution function as given in Formula (3) for urban and rural
environments
urban rural
A B A B
qd qd
() ()
3u i 3r i
d 0,3 μm 10 μm d 0,25 μm 11 μm
50,u 50,r
σ σ
2,2 3,1 2,2 4
gu, gr,
y 0,45 y 0,18
u r
Figure 1 shows a graphical plot of Formula (3) using the parameters given in Table 2.
Key
logarithmic distribution (this standard)
logarithmic distribution (cumulative)
Figure 1 — Discrete and cumulative logarithmic particle volume distribution functions of ambient
aerosol as typically found in urban and rural environments (see Reference [7])
As an example, Table 3 gives the values of the standardized proportion by volume, q , calculated using
Formula (3) for the particle counter channels recommended by ISO 16890-2.

ISO/DIS 16890-1:2025(en)
Table 3 — Example of the standardized urban and rural particle volume distributions, q , in
ambient air for the particle size channels recommended by ISO 16890-2
Optical particle diameter in µm Discrete particle volume distribution
d d Δlndd=ln /d urban rural
()
i i+1 dd=⋅d
ii+1 i
ii i+1
qd qd
() ()
3u i 3r i
0,30 0,40 0,35 0,29 0,226 27 0,094 12
0,40 0,55 0,47 0,32 0,198 91 0,083 95
0,55 0,70 0,62 0,24 0,158 37 0,074 32
0,70 1,00 0,84 0,36 0,115 22 0,070 14
1,00 1,30 1,14 0,26 0,085 03 0,076 28
1,30 1,60 1,44 0,21 0,076 18 0,088 33
1,60 2,20 1,88 0,32 0,080 22 0,108 04
2,20 3,00 2,57 0,31 0,099 84 0,137 26
3,00 4,00 3,46 0,29 0,126 88 0,167 08
4,00 5,50 4,69 0,32 0,155 56 0,195 42
5,50 7,00 6,20 0,24 0,177 57 0,216 71
7,00 10,0 8,37 0,36 0,191 57 0,231 43
NOTE The differences between aerodynamic and optical particle diameters are neglected in this document.
Additionally, it is assumed that the particle density is constant while in actual ambient air it may depend on the
particle size.
7.2 Calculation of the particulate matter efficiencies (ePM)
The particulate matter efficiencies ePM , ePM and ePM are calculated from the average fractional
10 2,5 1
efficiencies E , [see Formula (1)] and the standardized particle size distribution defined in 7.1 [see
A,i
Formula (3)] by using Formula (4).
n n
eEPM =⋅qd ⋅ΔΔlndq/ldd⋅ n (urban size distribution),
() ()
1 Au,ii3 i 3u ii
∑∑
i==1 i 1
n n
eEPM =⋅qd ⋅ΔΔlndq/ldd⋅ n (urban size distribution),
() ()
25,,∑∑Auii3 i 3u ii
i==1 i 1
n n
eEPM =⋅qd ⋅ΔΔlndq/ldd⋅ n (rural size distribution) (4)
() ()
10 Ar,ii3 i 3r ii
∑∑
i==1 i 1
where dd=⋅d is the geometric mean diameter and Δlndd=−ln lndd=ln()/d
ii i+1 ii++11ii i
In Formula (4), i is the number of the channel (size range) of the particle counter under consideration and n
is the number of the channel (size range) which includes the particle size, x (d < x ≤ d ), where x = 10 µm
n n+1
for ePM , x = 2,5 µm for ePM and x = 1 µm for ePM . For the determination of the efficiency ePM , the
10 2,5 1 1
upper limit of the largest channel considered in Formula (4) shall be equal to 1 µm (d = 1 µm); for ePM
n+1 2,5
it shall not be larger than 3,0 µm (d ≤ 3,0 µm). To determine the efficiency, ePM , the upper limit of the
n+1 10
largest channel considered in Formula (4) shall be equal to 10 µm (d = 10 µm). The lower size limit of the
n+1
smallest channel of the particle counter taken into account for the calculation of the efficiency values, ePM
x
shall be equal to 0,3 µm (d = 0,3 µm). The minimum number of channels considered in Formula (4) shall be
3 for ePM (n ≥ 3), 6 for ePM (n ≥ 6) and 9 for ePM (n ≥ 9). In any case, all channels used shall be adjacent
1 2,5 10
not missing out or overlapping any particle size in-between.

ISO/DIS 16890-1:2025(en)
Additionally, the minimum efficiencies, ePM and ePM are defined by Formula (5).
2,5, min 1, min
n n
eEPM =⋅qd ⋅ΔΔlndq/ldd⋅ n (5)
() ()
x,min ∑∑Du,ii3 i 3u ii
i==1 i 1
7.3 Classification
The initial arrestance and the three efficiency values ePM , ePM and ePM and the minimum efficiency
1 2,5 10
values ePM and ePM shall be used to classify a filter in one of the four groups given in Table 4.
1, min 2,5, min
Table 4 — Filter groups
Requirement
Class reporting
Group designation
value
ePM ePM ePM
1, min 2,5, min 10
Initial grav.
ISO Coarse — — <50 %
arrestance
ISO ePM10 — — ≥50 % ePM
ISO ePM2,5 — ≥50 % — ePM
2,5
ISO ePM1 ≥50 % — — ePM
The filter classes are reported as class reporting value in conjunction with the group designation. For the
reporting of the ISO coarse and ePM classes, the class reporting values shall be rounded downwards to the
nearest multiple of 5 % points. Values larger than 95 % are reported as “>95 %”. Examples of reporting
classes are ISO Coarse 60 %, ISO ePM10 60 %, ISO ePM2,5 80 %, ISO ePM1 85 % or ISO ePM1 >95 %. Except
for filters of the group ISO Coarse, the dust loading in accordance to ISO 16890-3 and the measurement of
the initial arrestance is optional. ISO coarse filters can be classified only based on the initial arrestance and,
hence, in this case, the measurement of the ePM efficiency values is optional.
x
NOTE When the test is carried out on a test rig which was originally designed to perform tests only using an
aerosol consisting of untreated and undiluted DEHS or an equivalent liquid test aerosol for the size range from 0,3 µm
to 1 µm, for an ISO ePM1 dust filter (ePM ≥ 50 %), it is allowable only to report the efficiencies ePM and ePM
1, min 1, min 1
and, in this case, only to use these two values to determine the filter group and class.
Based on the test results and Table 4, filters could be assigned to two or more filter groups. For example,
a filter classified as ISO ePM1 85 % could also be classified as ISO ePM10 95 %. However, according to this
part of ISO 16890, filters shall be classified into one individual group only and only this one classification
shall be shown on the filter’s label. Nevertheless, in a full summary report, all five ePM efficiency values
x
shall be reported, namely the three efficiency values ePM , ePM and ePM and the minimum efficiency
1 2,5 10
values ePM and ePM . The reporting of the initial arrestance is optional, except for ISO Coarse
1, min 2,5, min
filters, where this value determines the filter class and, hence, its reporting is mandatory. The efficiency
comparison of different filters shall be done only within the same ISO group, e.g. comparing ePM of filter A
with ePM of filter B.
8 Reporting
8.1 General
Data given in the summary report are based on the data and test reports generated from ISO 16890-2,
ISO 16890-3 and/or ISO 16890-4 and the data analyses and classification defined in 7.3. At a minimum,
the summary test report shall include a description of the test method(s) and any deviations from it. The
summary report shall include the following:
— type of filter;
— the number of this part of ISO 16890;
— test number;
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