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covers fm BRITISH STANDARD BS EN 13528 3 2003 Ambient air quality — Diffusive samplers for the determination of concentrations of gases and vapours — Requirements and test methods — Part 3 Guide to se[.]

Ambient air quality —

Diffusive samplers for

This British Standard, was

published under the authority

of the Standards Policy and

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EUROPÄISCHE NORM

ICS 13.040.20

English version

Ambient air quality - Diffusive samplers for the determination of

concentrations of gases and vapours - Requirements and test

methods - Part 3: Guide to selection, use and maintenance

Qualité de l'air - Echantillonneurs par diffusion pour la

détermination de concentration des gaz et vapeurs

-Exigences et méthodes d'essai - Partie 3: Guide pour la

sélection, l'utilisation et la maintenance

Außenluftqualität - Passivsammler zur Bestimmung der Konzentrationen von Gasen und Dämpfen - Teil 3:Anleitung zur Auswahl, Andwendung und Handhabung

This European Standard was approved by CEN on 3 November 2003.

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 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 Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2003 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members.

Ref No EN 13528-3:2003 E

Contents page

Foreword 4

Introduction 5

1 Scope 6

2 Normative references 6

3 Terms and definitions 6

4 Symbols and abbreviations 7

5 Measurement objectives and strategy 8

5.1 Measurements in support of Community Policy 8

5.1.1 Air Quality Directives 8

5.1.2 Source-related assessment 9

5.1.3 Forest Protection directives 10

5.1.4 Protection of ecosystems 10

5.1.5 Public awareness 10

5.2 Measurement in support of other policies 10

5.2.1 Measurement in support of national, regional or local policies 10

5.2.2 Protection of special ecosystems 10

5.2.3 Particular research aspects 10

5.3 Measurement strategy 11

6 Selection of the device 11

6.1 Sources of information 11

6.2 Selection of a sampler and procedure 11

6.3 Specific applications 12

6.4 Compliance with parts 1 and 2 of this standard 12

7 Operating principles 12

7.1 Principles of diffusive sampling 12

7.2 Dimensions of diffusive uptake rate 13

7.3 Bias due to the selection of a non-ideal sorbent 13

7.4 Environmental factors affecting sampler performance 14

7.4.1 Temperature and pressure 14

7.4.2 Humidity 14

7.4.3 Transients 15

7.4.4 Influence of air velocity 15

7.4.5 Transportation 16

8 Protection from adverse environmental conditions 16

8.1 General 16

8.2 Air velocity 16

8.3 Precipitation 16

8.4 Provision of a shelter 17

8.5 Security 17

9 Arrangement of sampling points 17

10 Requirements for training 17

11 Quality assurance 18

Annex A (informative) Specific applications 19

A.1 General 19

A.2 Nitrogen oxides 19

A.2.1 Tube-type samplers 19

A.2.2 US Environmental Protection Agency (EPA)/Monsanto badge 19

A.3 Nitrogen monoxide 20

A.4 Sulphur dioxide 20

A.5 Ammonia 21

A.6 Organic gases (Volatile Organic Compounds or VOCs) 21

A.6.1 Tube-type samplers 21

A.6.2 Badge-type samplers 22

A.6.3 Radial samplers 22

A.7 Formaldehyde 22

A.8 Ozone 23

A.9 Shelters 23

A.10 Design of Standard Atmosphere Apparatus 28

Annex B (informative) Characteristics of some diffusive samplers 29

Bibliography 32

This document (EN 13528-3:2003) has been prepared by Technical Committee CEN/TC 264 “Air quality”, thesecretariat of which is held by DIN

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 2004, and conflicting national standards shall be withdrawn at the latest byJune 2004

This European Standard is a multi-part standard having the following parts:

EN 13528-1, Ambient air quality Diffusive samplers for the determination of concentrations of gases and vapours Requirements and test methods - Part 1: General requirements

-EN 13528-2, Ambient air quality Diffusive samplers for the determination of concentrations of gases and vapours Requirements and test methods - Part 2: Specific requirements and test methods

-EN 13528-3, Ambient air quality Diffusive samplers for the determination of concentrations of gases and vapours Requirements and test methods - Part 3: Guide to selection, use and maintenance

-Annexes A and B of this part of the European Standard are informative

This document includes a Bibliography

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,Slovakia, Spain, Sweden, Switzerland and the United Kingdom

Introduction

This European Standard specifies requirements and test methods for the determination of performancecharacteristics of diffusive samplers used for the determination of concentrations of gases and vapours in ambientatmospheres

With regard to air quality, the objectives fixed in the 5th Action Program of the European Union are for the effectiveprotection of all people against recognised risks from air pollution and the establishment of permitted concentrationlevels of air pollutants, which should take into account the protection of the environment These objectives includemonitoring and control of concentrations with regard to standards

Successive programs of action of the European Union on the protection of the environment have stressed the need

to find a balance between the use of different tools: product standards, emission limits and environmentalobjectives/standards

The implementation of existing Directives has highlighted the existence of various problems, which are beingaddressed in the Council Directive on Ambient Air Quality Assessment and Management [1] These include:

 different monitoring strategies in comparable situations between and within Member States;

 harmonisation of measuring methods;

 quality of the measurements which depend on the calibration and quality assurance procedures

Diffusive samplers used to measure air quality should fulfil some general requirements which are given in

EN 13528-1 These requirements include unambiguity, selectivity and Data Quality Objectives, including

Although this standard specifically addresses ambient air, diffusive sampling is also relevant to the assessment ofair quality in indoor air Both pumped and diffusive sampling procedures are considered appropriate for suchmeasurements, depending on circumstances (particularly any requirement for time resolution) [2] prEN 14412gives guidance on the selection, use and maintenance of diffusive samplers used to measure indoor air quality.This part of EN 13528 is similar in content to EN 838 and EN 13528-1 is similar in content to EN 482 The series ofstandards on the use of diffusive samplers for ambient air has been created in addition to those for workplace airbecause the underlying European Directives are different and the consequent definitions and practical applications

of the estimation of the uncertainty of measurements are different

1 Scope

This part of the European Standard gives guidance on the selection, use and maintenance of diffusive samplersused to measure ambient air quality It includes guidance on measurement objectives and strategies, both insupport of European Community Policy and more generally, relevant to the use of such samplers It also includesinformation on the operating principles of diffusive samplers and the factors that affect performance in the practicalimplementation of such policies Advice is also given on ways to minimise any such adverse effects, e.g bysuggesting shelters that may protect against the effects of wind speed on the samplers, and on training and qualityassurance considerations

Annexes give further information on practical applications for particular environmental pollutants, including thosespecified by existing and anticipated European Daughter Directives

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision For undated references the latest edition of thepublication referred to applies (including amendments)

ENV 13005, Guide to the expression of uncertainty in measurement

EN 13528-1:2002, Ambient air quality - Diffusive samplers for the determination of concentrations of gases andvapours - Requirements and test methods - Part 1: General requirements

EN 13528-2:2002, Ambient air quality - Diffusive samplers for the determination of concentrations of gases andvapours - Requirements and test methods - Part 2: Specific requirements and test methods

ISO 5725 (all Parts), Accuracy (trueness and precision) of measurement methods and results

3 Terms and definitions

NOTE Attention is drawn to the fact that the terms Assessment, Limit Value and Pollutant are defined in Directive 96/62/EC[1]

For the purposes of this European Standard the following terms and definitions apply

NOTE 1 Active normally refers to the pumped movement of air

NOTE 2 This definition differs from that in EN 838 by the addition of the words “or a porous material”

3.4

diffusive uptake rate

rate at which the diffusive sampler collects a particular gas or vapour from the atmosphere, expressed in picogramsper parts per billion1 per minute (pg ppb-1 min-1) or cubic centimetres per minute (cm3 min-1)

NOTE 1 pg ppb-1 min-1 are equivalent to ng ppm-1 min-1

NOTE 2 This definition differs from that in EN 838 by the substitution of “picograms per parts per billion” for “nanograms perparts per million” The expression is numerically the same, but ambient concentrations are usually in the ppb range

uncertainty (of measurement)

parameter, associated with the results of a measurement, that characterises the dispersion of values that couldreasonably be attributed to the measurand

NOTE 1 The parameter can be, for example, a standard deviation (or given multiple of it), or the half width of an intervalhaving a stated level of confidence

NOTE 2 Uncertainty of measurement comprises, in general, many components Some of these components can beevaluated from the statistical distribution of the results of a series of measurements and can be characterised by experimentalstandard deviations The other components, which can also be characterised by standard deviations, are evaluated fromassumed probability distributions based on experience or other information

NOTE 3 It is understood that the result of a measurement is the best estimate of the value of a measurand, and that allcomponents of uncertainty, including those arising from systematic effects, such as components associated with corrections andreference standards, contribute to this dispersion [ENV 13005]

3.8

validation

process of evaluating the performance of a measuring procedure and checking that the performance meets certainpre-set criteria

4 Symbols and abbreviations

A cross-sectional area of the diffusion path, or equivalent sorption surface, in square centimetres;

C observed concentration, in micrograms per cubic meter;

D diffusion coefficient of analyte, in square centimetres per minute;

D1 diffusion coefficient of analyte 1, in square centimetres per minute;

D2 diffusion coefficient of analyte 2, in square centimetres per minute;

l length of static air layer in sampler (or equivalent for permeation types), in centimetres;

M molar mass of analyte, in grams per mol;

mb mass of the analyte which is desorbed from the blank sampler, in picograms;

md mass of the analyte which is desorbed from exposed samplers, in picograms;

ms mass of the analyte which is sorbed by diffusion, in picograms;

P pressure of the sampled atmosphere during sampling, in kilopascals;

t exposure time, in minutes;

T temperature of the atmosphere sampled, in Kelvin;

U diffusive uptake rate, in cubic centimetres per minute;

U1 diffusive uptake of analyte 1, in cubic centimetres per minute;

U2 diffusive uptake of analyte 2, in cubic centimetres per minute;

U' diffusive uptake rate, in picograms per parts per billion per minute (pg ppb-1 min-1);

V volumetric flow of air, in cubic meters per minute;

δ bias;

φ delivered concentration in parts per billion (volume fraction = 10-9);

ρ delivered concentration, in micrograms per cubic meter;

ρ1 concentration of the given analyte at the beginning of the diffusion layer (l = 0), in micrograms per cubic

meter;

ρ2 concentration of the given analyte at the end of the diffusion layer, in micrograms per cubic meter;

τ time constant of the diffusive sampler, in seconds

5 Measurement objectives and strategy

5.1 Measurements in support of Community Policy

NOTE It is the responsibility of the user of the standard to check the latest developments of EU legislation

5.1.1 Air Quality Directives

Different regimes of air quality assessment are possible for the implementation of the Council Directive on AmbientAir Quality Assessment and Management [1], and successive Daughter Directives, in which the measurementrequirements are relaxed as the risk of exceeding the limit values decreases

Measurements at fixed measuring stations, indicative measurement methods, emission inventories and air qualitymodelling, or a combination of techniques, may be used, depending on whether the pollutant concentration levelsover a representative period are above or below one or more set percentages of the relevant limit value Generally,the closer the concentration is to the limit value, the more demanding are the data quality objectives (see below).The percentages, for both the upper and lower assessment thresholds, as defined in EC-Directive 96/62/EC [1], are

The uncertainty (at a 95 % confidence interval) of the assessment methods will be evaluated in accordance withthe Guide to the Expression of Uncertainty in Measurement (ENV 13005) and/or ISO 5725 or equivalent.

The diffusive sampling technique may be implemented under the Air Quality Directives for:

 classification of zones (Art 8 and 9);

 preliminary assessment of ambient air quality (Art 5);

 network design/optimisation (Art 4.3);

 air quality monitoring in areas at no risk of exceeding limit values (Art 6.3);

 determination of areas of homogeneous air quality;

 assessment of pollution in the vicinity of point sources (traffic, industry);

 assessment of pollution in ecosystems

Further guidance on the potential of diffusive sampling in connection with Preliminary Assessment under EC AirQuality Directives is given in the report [6]

Detailed requirements for the assessment of concentrations of atmospheric pollutants, with special reference to thepotential of diffusive sampling, have been developed by VDI [7]

5.1.2 Source-related assessment

Diffusive sampling is already established within industry for workplace monitoring [EN 482]; however thetechniques have yet to be widely accepted for monitoring of ambient air within industrial areas

In addition to the tasks mentioned in 5.1.1 diffusive sampling can be used for:

 environmental Impact Assessments studies needed to obtain exploitation permits;

 measurement campaigns for the identification of sources;

 surveys to monitor the environmental impact of industrial processes within plants;

 ground level air quality impact of factory sites by deployment at boundary fences;

 air quality monitoring campaigns with local authorities within communities and rural areas neighbouring majorindustrial complexes to demonstrate compliance with and maintenance of air quality objectives in ECDirectives and national air quality standards

Diffusive samplers are already available for various substances and/or can be designed to measure almost allgases emitted by industrial and other processes, including oxides of nitrogen and sulphur, ammonia and amines,chlorinated hydrocarbons, oxygenated species including solvents and aldehydes, halogen and acid gases,hydrogen sulphide and many others (annex A)

5.1.3 Forest Protection directives

Diffusive sampling is also relevant to the Council Regulation (EEC) No 3528/86 (amended by Regulation (EEC)

No 2157/92) on the protection of the Community's forests against atmospheric pollution, and establishing anetwork of permanent observation sites for the intensive and continuous surveillance of forest ecosystems [8]

5.2 Measurement in support of other policies

5.2.1 Measurement in support of national, regional or local policies

A limited number of local authorities in Member States have already taken pro-active measures to assess ambientair quality within their urban and rural environments However, measurements methods used to date tend to bebased on fixed point monitoring stations which are only partly representative of the spatial variations in ambient airquality Determining the spatial location of such sites can be difficult In addition, such techniques are expensive.Diffusive sampling provides an excellent tool for screening campaigns to estimate air quality at many locationssimultaneously An example is given in [9, 10; other examples available in literature] Such campaigns complementdata obtained from fixed stations such that a local authority can confidently assess local ambient air conditions andmake decisions about network design for future campaigns

5.2.2 Protection of special ecosystems

Special sensitive ecosystems such as natural reserves and mountain areas are not specifically covered by existingCommunity limit values or national air quality regulations but may be protected by particular and more stringentregulations The simplicity of operation of the diffusive sampling technique and the lack of a requirement for electricpower renders this technique well adapted to this scope, in particular for the assessment of integrated pollutionlevels over longer periods of time

The technique can similarly be used for the protection of our cultural heritage (historical, monuments, paintings,etc.)

5.2.3 Particular research aspects

Diffusive samplers can be used in response to particular research needs, such as for:

 analysis of trends in air quality;

 study of the source/receptor relationship;

 validation of atmospheric dispersion models;

 evaluation of emission reduction measures;

 collecting exposure data for epidemiology or risk assessment

5.3 Measurement strategy

The measuring strategy will depend on the objectives of the monitoring, and the pollutants to be assessed It isnecessary to specify where, how, and how often measurements shall be taken The measuring effort will bedependent on:

 variation of pollutant concentrations in space and time;

 availability of supplementary information;

 accuracy of the estimate that is required

A practical example of the development of a measurement strategy in connection with Preliminary Assessmentunder EC Air Quality Directives is given in the report [6]

6 Selection of the device

6.1 Sources of information

Important information on the performance characteristics of a diffusive sampler can be obtained from varioussources These include:

 manufacturer's instructions for use (EN 13528-2:2002, 5.12);

 published commercial technical information;

 technical and research publications;

 national and international standards [11-15];

 user groups, e.g HSE/CAR/WG 5 (Health and Safety Executive / Committee on analytical Requirements/Working Group 5), which issues The Diffusive Monitor, a newsletter produced since 19882

6.2 Selection of a sampler and procedure

The selection of a diffusive sampler will depend on many factors These include:

a) measurement task (clause 5); i.e

 mandatory measurements;

 indicative measurements;

 objective assessment;

 measurements other than required by the Framework Directive[1];

b) specified measuring range required, with special reference to the sampling time, the detection limit, the uptakerate and the possibility of reaching the equilibrium saturation capacity of the sorbent medium of the sampler(see annex B);

c) time resolution required;

2 obtainable from the Health and Safety Laboratory, Broad Lane, Sheffield S3 7HQ, UK

d) selectivity to the target gas or vapour and sensitivity to interfering gases and vapours (EN 13528-1:2002, 5.2);e) relevant Data Quality Objectives (EN 13528-1 :2002, 5.3);

f) susceptibility of the sampler to environmental factors (7.4), particularly air velocity;

g) adequate protection from adverse environmental conditions (see clause 8);

h) fitness for purpose, e.g size, weight, durability (see 6.4);

i) training requirements for the reliable operation, maintenance and calibration (see clause 10);

j) total cost of purchase and operation, including calibration and maintenance;

k) compliance with the performance requirements of Parts 1 and 2 and appropriate national regulations (see 6.4);l) conformity to the user's quality system (see clause 11)

6.3 Specific applications

Specific applications of diffusive samplers for environmental pollutants are given in annex A

6.4 Compliance with parts 1 and 2 of this standard

Marking EN 13528 on or in relation to a product represents a manufacturer's declaration of conformity, i.e a claim

by or on behalf of the manufacturer that the product meets the requirements of this European Standard Theaccuracy of the claim is therefore the responsibility of the person making the claim

7 Operating principles

7.1 Principles of diffusive sampling

The mass of the analyte which can diffuse to a suitable sorbent within a certain time is determined by the equationwhich is derived from Fick's first law of diffusion:

( )

tD

Figure 1 — Diagram of diffusion process

The inlet of a sampler with cross-section A at position 1 defines the beginning of the diffusion path of an analytewith a concentration of ρ1 A sorbent B at position 2, which will reduce the concentration of the analyte, ρ2, to zero(ideally) due to sorption or chemical reaction, serves as the driving force for the diffusion along l

In practice, there are a number of factors that can give rise to non-ideal behaviour, so that:

l

ktD

A

ms = × ×ρ× ×

(1b)

NOTE k can be a function of concentration and time of exposure (see 7.3)

A general overview of the principles of diffusive sampling is given in [16]

7.2 Dimensions of diffusive uptake rate

For a given concentration ρ in micrograms per cubic metre of gas or vapour, the diffusive uptake rate is given by:

PM

U

'

7.3 Bias due to the selection of a non-ideal sorbent

The performance of a diffusive sampler depends critically on the selection and use of a suitable sorbent In thecase of a collection medium, which has high sorption efficiency, the residual vapour pressure of the sampled

compound at the sorbent surface (ρ2) will be very small in comparison to the ambient concentration The observeduptake rate will then be close to its ideal steady-state value, which can usually be calculated from the geometry ofthe sampler and the diffusion coefficient of the analyte in air.

In the case where a weak sorbent is used, then ρ2 in equation 1a is non-zero and ms/ will decrease with the time ofsampling In the alternative expression, equation 1b, k has a value significantly less than unity Hence U inequations 2 will also decrease with the time of sampling The concentration of the sampled pollutant can also have

a (lesser) effect on ms/ and hence on U The magnitude of these effects is dependent on the adsorption isotherm

of the analyte and sorbent concerned, and may be calculated with the aid of computer models [17,18]

Another manifestation of the same effect is back diffusion, sometimes called reverse diffusion This can happenwhere, some time after sampling has started, the vapour pressure of the analyte at the sorbent surface, ρ2, isgreater than the external concentration, ρ1, for example if a sampler is first exposed to a high concentration andthen to a much lower or even zero concentration This type of exposure profile can occur in certain applications,and the magnitude of any error introduced will depend on whether the period of high concentration occurs at thebeginning, middle, or end of the sampling period The phenomenon has been discussed in detail by Bartley andothers [19-21] and a simple test proposed [22] to give an estimate of the maximum bias to be expected between apulsed exposure and an exposure to a constant concentration, which latter normally provides the basis for thesampler calibration This test is 30 min exposure to a high concentration, followed by 7,5 h of clean air, and hasbeen adopted in EN 838 For ambient air applications (EN 13528-2:2002, 7.3.1), however, it is considered that anexposure profile of alternate equal periods of high and low exposure for a 24-h cycle is more typical of the intendedapplication, where diurnal variations in concentration are common The extent of back-diffusion can also bemodelled theoretically [18,23]

It is therefore desirable to choose a sorbent with high sorption capacity and low vapour pressure of the sorbedmaterial or of the reaction product formed by a reactive sorbent

7.4 Environmental factors affecting sampler performance

7.4.1 Temperature and pressure

For an ideal diffusive sampler, the dependence of U on absolute temperature and pressure is governed by that ofthe diffusion coefficient of the analyte The latter dependence is given by:

l2

=

For most commercial samplers, τ is between about 1 s and 10 s

7.4.4 Influence of air velocity

7.4.4.1 Effect of low and high wind speeds

Wind speed and direction (i.e from the point of view of the sampler, the ambient air face velocity and the samplerorientation) can affect the performance of a diffusive sampler because they may influence the effective diffusionpath length [30-33] The diffusive mass uptake of a sampler (equation 1) is a function of the length, l, and the cross-sectional area, A, of the diffusion gap within the sampler The nominal diffusion path length is defined by thegeometry of the sampler and is the distance between the sorbent surface and the external face of the sampler Thecross-sectional area is also defined by the geometry of the sampler and if the cross-section of the diffusion gap isnot constant along its length, is defined by the narrowest portion The effective length, l, is not necessarily the same

as the nominal length, and may be greater or less, depending on circumstances

Under conditions of low external wind speeds, the effective diffusion path length may be increased [32,33] This isbecause a 'boundary layer' [30,31] exists between the stagnant air within the sampler and the moving air outsideand contributes to the effective diffusion path length, l In reality, there is an area outside the sampler where there is

a transition between static air and moving air, but this is equivalent to an extra length (∆l) of static air, which must

be included in the value of l The value of ∆l depends on the external geometry of the sampler It also decreaseswith increasing air velocity Its significance depends on the value of the nominal path length of the diffusivesampler Thus a sampler with a small cross-section and long internal air gap will be relatively unaffected by airvelocity, whilst a short, fat sampler will be significantly affected This is borne out in practice, as has beendemonstrated with samplers of varying length [32, 33] Low sampling rates are observed at low air velocities, butincrease to a plateau value as the boundary layer effect becomes insignificant

Under conditions of high external wind speeds, the effective diffusion path length may be decreased [34, 35-40].This is because external high airflows disturb the static air layer within the sampler, which reduces the effective airgap by a (different) factor ∆l The value of ∆l is small, provided the length to diameter ratio of the sampler air gap isgreater than 2,5 to 3 [34], or it can be avoided, or greatly reduced, by incorporating a draught shield, e.g astainless steel screen or plastic membrane An alternative to using a draught shield is to place the sampler in aprotective housing, but in this case, the housing shall completely surround the sampler (see also 8.4)

The overall effect is therefore an s-shaped curve (EN 13528-2:2002, 7.4, Figure 1)

7.4.4.2 Consequence for different sampler geometries

Tube-type samplers are typically unaffected by low air velocities [25, 41,42] but those without a draught shield may

be affected by high speeds

Badge-type samplers generally have a large surface area and small air gap, so that they may be more affected byair velocity than tube designs and typically require a minimum face velocity of between 0,5 m⋅s-1 and 0,2 m⋅s-1 [43-46] Some badges with an inadequate draught shield are also affected at high air velocities [42, 44, 47].

Radial diffusive samplers [48, 49] require a minimum face velocity of about 0,25 m⋅s-1

7.4.5 Transportation

Most samplers will require transportation between the sampling site and an analytical laboratory, so that it isimportant that sample integrity is maintained during this process The following precautions are recommended:a) Ensure that any seals are sufficiently tight to avoid ingress of contamination or loss of sample during transit:metal - plastic seals may become loose if a large temperature change takes place;

b) Place the samplers in inert closed containers to minimise the ingress of external contamination;

c) If air-freighting samples, ensure that they are not subjected to negative pressure, e.g in the baggage hold;d) Avoid exposure to high temperatures during transit, e.g in the boot of a car;

e) If possible, keep the samplers at low temperature, low humidity and away from contamination sources e.g.fuels, but avoiding condensation on the sample

Ensure that adequate sample blanks are transported with the samples so that any of the above problems can beidentified

8 Protection from adverse environmental conditions

at low wind speeds would be magnified in the time-weighted average

For samplers which are affected at low wind speeds, and if exposure to such conditions is likely to be significant,then some additional ventilation is necessary This could be achieved by using a small fan for forced ventilation:this might defeat the object of using a 'passive' sampler, but could be practicable with solar power in more southernclimates Alternatively, samplers might be suspended on a fine thread to increase the effect of small air movements[53]

Similarly, for samplers which are affected at high wind speeds, some attenuation of the air velocity is necessary.Even where moderate wind speeds are expected, problems can arise if samplers are placed too close to buildings

or other obstacles Consideration shall be given to the size and location of the obstacle(s) in the sitting of thesampler (see clause 9)

8.3 Precipitation

Protection from precipitation is important for all types of sampler Rain or melted snow can block the samplingsurfaces [54], particularly of tube samplers oriented vertically downwards (which is the usual position to avoidingress of particulates)

 the design of the shelter and the means of locating the sampler shall not significantly affect the diffusive uptakerate of the sampler;

 the construction, surface and colour of the shelter shall be such to minimise temperature rise due to directsolar radiation

An alternative to providing a shelter is to modify the diffusive sampler For example, the diffusion end cap of a type sampler can be modified with the addition of an aluminium brim to prevent rainwater blocking the diffusionsurface [55] However, such an arrangement may modify the performance characteristics of the sampler withrespect to the minimum air velocity requirement

tube-8.5 Security

Security is also a major consideration, as samplers exposed for long periods in public or semi-public places aresubject to theft and vandalism Samplers should be sited, so far as possible, to be out of reach, inconspicuousand/or designed to look like something else, e.g the nest box idea

9 Arrangement of sampling points

The number, location and height of sampling points should be selected in such a way, as a function of themeasurement task, that answers to the specific questions posed can reasonably be expected Once chosen, thesampling points should not be changed during the measurement programme

Unless otherwise specified, suitable sampling points should be at least 1 m away from buildings or other majorobstructions to avoid local perturbation effects The measuring height should be between 1,5 m and 4,0 m: at least2,5 m will discourage theft and vandalism The immediate vicinity of trees, bushes, etc should be avoided tominimize the influence of the local environment or to minimize effects from troublesome insects

10 Requirements for training

For most apparatus, specialist training is required for both the operator and those responsible for the maintenanceand calibration Diffusive samplers, however, do not require a specialist operator for their deployment, provided thatclear and unambiguous instructions for use are available (see EN 13528-2:2002, 5.10) and due note is taken of theabove guidance A minimum of practical training is indispensable for operators to avoid common errors likesmoking during work, working directly near a car with its engine running, touching inner surfaces of the samplerwith the fingers, or using felt-tip pens for marking

Maintenance, however, is as important for diffusive samplers as for other devices, and particular attention should

be made to the following:

a) For re-usable devices, ensure that the collection element is intact, clean, or replaced as necessary;

b) Ensure that all component parts are free from contamination;

c) Ensure that the devices are used in accordance with EN 13528-1 and EN 13528-2;

d) Ensure that devices are used within the manufacturer's recommended shelf-life

11 Quality assurance

It is good practice to set up a quality assurance scheme for the maintenance and calibration of the samplers Thisincludes:

a) the establishment of a Standard Operating Procedure (SOP);

b) for re-usable devices, a log of usage;

c) keeping a record of the traceability of the calibration;

d) retaining the raw data as required by the quality or other system;

e) using a unique sampler numbering system Re-usable samplers shall be in addition labelled with a durableidentification;

f) depending on the measurement task, taking an appropriate number of field blank and replicate samples (e.g

10 %);

g) for internal QA, to check diffusive sampling rates routinely; at least once during large surveys This may bedone by exposing samplers in laboratory standard atmospheres or by laboratory or field comparisons with anindependent (e.g pumped) method (see A.10);

h) for external QA, to check diffusive sampling rates routinely; at least once during large surveys This may bedone by laboratory or field intercomparisons, which should be conducted by experienced institutes (see A.10);i) sampling protocol including relevant information on sampling such as measurement location, measurementperiod, sampler identification, operator

This annex gives some examples of practical applications of diffusive samplers for the monitoring of ambient air It

is intended a guide to sources of information (see 6.1) and should not replace the evaluation of the suitability of aparticular device for a particular application as described in 6.2 The source references should be consulted beforeoperational use of the devices A summary of the characteristics of some available diffusive samplers is given inannex B

The following information, whilst intended to be as comprehensive as possible, of necessity only reflects part of arapidly increasing literature Important new developments may therefore be missing or only partly described Themain text is restricted to a brief description of the main devices available, important advantages or limitations andvalidation status In most cases, a full validation according EN 13528-1 and EN 13528-2 has not been conducted(since the standard was not available at the time) and this should be borne in mind when selecting suitable devices

A.2 Nitrogen oxides

A.2.1 Tube-type samplers

A common form of tube-type diffusive sampler used for a number of acid gases is the device commonly termed the'Palmes tube' [35] It consists of a simple acrylic tube, about 8 cm by 1 cm id., with one closed end Sampled gasesenter the tube at the open end, migrate down the tube by molecular diffusion and are collected at the closed end by

an (efficient) sorbing medium, in this case triethanolamine (TEA; 2,2',2"-nitrilotriethanol) coated on stainless steelgrids In the case of NO2, it is trapped as a complex with TEA and frequently is measured spectrophotometricallyafter reduction to nitrite and reaction with sulphanilamide and naphthylethylenediamine The trapped NO2 can also

be measured by ion chromatography [56]

The Palmes tube is very simple and cheap, but in the open tube version is susceptible to high wind speeds [57] Itcan also have blank problems [56, 58, 59] and peroxyacetyl nitrate can be a positive interferent [60] Heal et al [61,62] have noted a possible positive interference of reduced NO2 photolysis in opaque Palmes tubes, leading to ahigher level of NO2 within the tube than outside (as the equilibrium with NO and ozone is disturbed)

Many authors have shown good agreement with alternative measurement methods in field intercomparisons [36,

59, 63, 64]

The sampler provides the basis for extensive monitoring networks, for example that in the UK [65]

Another device operates on a similar principle (AnalystTM3) [66] The device makes use of activated carbon andsolvent desorption, and is designed so that the desorption takes place in the sampling device, thus avoiding thetransfer of sorbent

A.2.2 US Environmental Protection Agency (EPA)/Monsanto badge

There are several different badge designs of differing geometry, but their basic principles are the same One suchbadge was described by Mulik et al [67] Their 'high efficiency passive sampling device' (PSD) consisted of a series

3 Analyst is an example of a suitable product available commercially (trade name of CNR - Italy) This information is given forthe convenience of users of this European Standard and does not constitute an endorsement by CEN of this product

of diffusion barriers placed on either side of a cavity for containment of the collection element, in this case a 33 mmdiameter reagent-coated glass filter paper TEA was used as the reagent for NO2 An alternative device is thatdeveloped by Krochmal and Górski [68] This has an internal diameter of 25 mm and a diffusive path length of 10

mm It also uses a TEA-impregnated glass fibre disc as the NO2 collection element The authors report on humidityand temperature effects The method forms the basis of a Polish Standard [69] A third device has been developed

by Kasper-Giebl et al [70] De Santis has developed a dual badge system [71] to a design by Willems [72]

Such samplers have higher intrinsic sampling rates that tube-types, so exposure periods can be shorter Since thechemistry is the same, chemical effects and interferences will be similar Moschandreas et al [73] found no effect

of temperature or humidity for the Mulik badge, except at extremes of temperature However, Krochmal and Kalina[74] found a significant temperature effect for NO2 (but not for SO2)

Many authors have shown good agreement with alternative measurement methods in field intercomparisons [72,73]

A.3 Nitrogen monoxide

In principle the Palmes tube can also be used to monitor NO if oxidised to NO2 Indeed, an early paper by Palmes[75] refers to a NOx sampler which monitors both NO and NO2 Sampled NO (together with any NO2) diffuses downthe tube, through the TEA-coated screen where it meets an oxidising layer and diffuses back as NO2 NO ismeasured by difference between tubes with and without oxidising layer In the Palmes version, the oxidising layer is

a chromic acid coated screen which has to be inserted immediately before sampling and removed immediatelyafterwards The same principle is used in a badge design by Ferber et al [76] (which incidentally predates theEPA/Monsanto badge)

A further device that can be used for both NO and NOx is marketed by Ogawa Hirano in Yokohama, Japan hasdeveloped the technology, not yet published It is a dual-faced sampler in which NO2 is determined on one side and

NOx on the other; NO is determined by difference TEA is used to collect NO2 and a proprietary reagent for NOx Ajoint study by US-EPA, the Harvard School of Public Health and ManTech Environmental Technology [77]demonstrated good agreement between Ogawa PSDs and weekly real-time averages from instrumental methods.Another device operates on a similar principle (AnalystTM4) [66] The device uses activated carbon as a collectingsurface and oxidation for NO by chromic acid

A.4 Sulphur dioxide

As noted above, the Palmes tube can also be used for monitoring sulphur dioxide Triethanolamine forms acomplex with SO2 as well as with NO2 and the product can be analysed by the para-rosaniline method or by ionchromatography after elution of TEA with a bicarbonate buffer Preliminary results [63] suggest a high correlationwith a fluorescence monitor under field conditions, but the response was only 50 % of the expected value Morerecently [78] problems were reported with storage recovery and the effect of relative humidity These problemshave now been largely overcome [79, 80] However, a new problem, that might be associated with the deposition ofparticulate sulphate onto the tube walls has been reported [81] Another device operates on a similar principle(AnalystTM4) [82] This device uses an alkaline coating and solvent desorption It is designed so that the desorptiontakes place in the sampling device, thus avoiding the transfer of sorbent

Similarly, several badge designs have been described Killick [83] evaluated the West badge [84] for ambient SO2

measurement in laboratory tests, sampling over 1-19 days He found generally good agreement with a continuousconductiometric instrument - in 75% of tests, the ratio of badge to instrument was between 0,80 and 1,17 Orr [85]modified the West badge to incorporate a porous (diffusion-limited) membrane rather than a silicone one and apotassium carbonate/glycerol impregnated filter rather than an absorption solution The modified badge had ahigher collection rate but also greater dependence on air velocity Also to gain higher sensitivity, Scheeren et al[86] used a short circular badge to a design by Willems [72] and investigated both TEA and potassium carbonate

4 Analyst is an example of a suitable product available commercially (trade name of CNR - Italy) This information is given forthe convenience of users of this European Standard and does not constitute an endorsement by CEN of this product