2008/50/EC - Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe

The European Air Quality Directive (Directive on ambient air quality and cleaner air for Europe) identifies different uses for modelling: Assessment, planning, forecast and source apportionment (SA). This CEN/TS addresses source apportionment modelling and specifies performance tests to check whether given criteria for receptor oriented source apportionment (RM) are met. The scope of the tests set out in this CEN/TS is performance assessment of SA of particulate matter using RM in the context of the European Directives 2004/107/EC and 2008/50/EC (AQD) including the Commission Implementing Decision 2011/850/EU of 12 December 2011. The application of RM does not quantify the spatial origin of particulate matter hence this CEN/TS does not test spatial SA.
This CEN/TS addresses RM users: participants and organisers of source apportionment intercomparison studies as well as practitioners of individual source apportionment studies. This CEN/TS is suitable for the evaluation of results of a specific SA modelling system with respect to intercomparison reference values (a-priori known or calculated on the basis of participants' values, see 3.12) in the following application areas:
- Assessment of performance and uncertainties of a modelling system or modelling system set up using the indicators laid down in this CEN/TS.
- Testing and comparing different source apportionment outputs in a specific situation (applying an evaluation dataset) using the indicators laid down in this CEN/TS.
- QA/QC tests every time practitioners run a modelling system.
It should be noted for clarity that the procedures and calculations presented in this CEN/TS cannot be used to check the performance of a specific SA modelling result without having any a-priori reference information about the contributions of sources/source categories.
The principles of receptor oriented models are summarised in Annex A. An overview of uncertainty sources and recommendations about steps to follow in SA studies are provided in Annex B and Annex C.
There are different methodologies than RM widely used to accomplish SA, e.g. source oriented models. These other methodologies cover aspects of SA which are required in the AQD and are not addressed by RM. Performance assessment of such methodologies is out of the scope of this CEN/TS.

This document describes procedures to assess the applicability of the standard method EN 16909 (determination of OC and EC deposited on filters) to particle size fractions up to 10 µm in aerodynamic diameter (50 % cut off).

This document provides
• information, guidance and specifications on how
o to set up an air quality and emissions management policy;
o to deploy reliable and scalable technologies to monitor air quality on a continuous or regular basis;
o to react with adequate measures;
o to specify air quality levels for triggering a scenario;
• a toolkit of parameters and data definitions that a regulator can use;
• means to measure the air quality required by relevant EU directives
• to specify use of TS Intelligent transport systems - Urban-ITS - 'Controlled Zone' management using C-ITS, for the purposes of geofenced controlled zones for emissions management
NOTE: In order to maximise European harmonisation, it is recommended that this specification is used in combination with a module of standardised data concepts, however, this version of this document, which is focussed on policies and procedures, does not provide these data concept specifications.

This document provides
• information, guidance and specifications on how
o to set up an air quality and emissions management policy;
o to deploy reliable and scalable technologies to monitor air quality on a continuous or regular basis;
o to react with adequate measures;
o to specify air quality levels for triggering a scenario;
• a toolkit of parameters and data definitions that a regulator can use;
• means to measure the air quality required by relevant EU directives
• to specify use of TS Intelligent transport systems - Urban-ITS - 'Controlled Zone' management using C-ITS, for the purposes of geofenced controlled zones for emissions management
NOTE: In order to maximise European harmonisation, it is recommended that this specification is used in combination with a module of standardised data concepts, however, this version of this document, which is focussed on policies and procedures, does not provide these data concept specifications.

This European Standard specifies a method for the determination of the mass concentration of water soluble NO3-, SO42-, Cl-, NH4+, Na+, K+, Mg2+, Ca2+ in PM2,5 as deposited on filters.
This European Standard describes a measurement method which comprises sampling of anions and cations as part of the PM2,5 particulate phase, sample extraction and analysis of anions and cations by ion chromatography.
NOTE 1   Alternatively, cations, excluding ammonium, can be analysed by inductively coupled plasma optical emission spectrometry (ICP-OES). Ammonium can also be analysed by photometry or conductometry.
This European Standard can be used for the measurements of anions and cations as required by Directive 2008/50/EC. The method does not take into account the possible losses  during sampling due to evaporation.
NOTE 2   NO3-, Cl-, NH4+ are part of the volatile fraction of PM2,5, and the concentrations determined using this standard can be used as minimum values for the concentrations of these ions in PM2,5. NO3-, NH4+, Cl- are usually 0 % to 30 % underestimated due to evaporational losses from the filter during sampling.
This European Standard may be used at rural and urban background sites and road sites that are in accordance with the siting criteria of Directive 2008/50/EC.
This European Standard is applicable to the measurement of anion/cations in PM2,5 samples corresponding to mass concentrations between approximately 1 μg/m3  (i.e. the limit of detection of the standard measurement method (EN 12341) expressed as its uncertainty) up to 120 μg/m3.
The validated range of the anion and cation concentrations based on the field validation measurements is presented in Table 1.
See Annex F for the statistical analysis of the field validation measurements.

This European Standard gives guidance on the measurement of elemental carbon (EC) and organic carbon (OC) following the requirement for the networks of all EU member states to measure EC and OC in particulate matter from June 2010 at background sites according to the Council Directive 2008/50/EC on ambient air quality and cleaner air for Europe [1].
This European Standard describes the analytical procedures for determining EC and OC on quartz fibre filters as μg/cm2, and the subsequent calculation of concentrations as µg/m3. Sampling onto filters is to be done in accordance with EN 12341:2014 for PM2,5. The sampling process determines the size fraction of the particulate matter, the retention of semi-volatile material, and uptake/loss of volatile organic compounds on the filter at the time of sampling.
The same analysis method may also be used for smaller size fractions than PM2,5. Any possible additional artefacts for larger particles, e.g. pyrolysis or higher concentrations of carbonates, should be assessed.
The scope includes rural background, urban background, road side and industrial measurement sites, to allow the assessment of additional exposure of people in urban areas as stated in the objectives of the council directive and to achieve coherence in the European approach.
The applicable concentration range of the proposed method is limited by the optical correction and instrument applied in the analysis of EC and OC. This method was validated from 0,2 µg CEC/cm² and 1,8 µg COC/cm² to 38 µg CEC/cm² and 49 µg COC/cm² in the laboratory and to 16 µg CEC/cm² and 45 µg COC/cm² in the field.

In order to be in compliance with EU Air Quality Directive requirements, the reference methods given in the Directive for the measurement of mass concentrations of particulate matter are not commonly used for operation in routine monitoring networks. These networks usually apply automated continuous measurement systems (AMS), such as those based on the use of oscillating microbalances or ß-ray attenuation, and on in-situ optical methods. Such AMS are typically capable of producing 24-hour average measurement values over a measurement range up to 1000 µg/m3 and 1-hour average measurement values up to 10000 µg/m3, if applicable, where the volume of air is the volume at ambient conditions near the inlet at the time of sampling.
The 1-hour average values may be used for:
- direct information of the public,
- aggregation to produce daily or yearly average concentration values for regulatory reporting purposes.
EU Air Quality Directive 2008/50/EC allows the use of such systems after demonstration of equivalence with the reference method, i.e. after demonstration that these systems meet the Data Quality Objectives for continuous measurements.
This standard lays down the minimum performance requirements and test procedures for the selection of appropriate AMS for particulate matter (type approval). This includes the evaluation of its equivalence with the reference method.
Further, this standard describes minimum requirements for ongoing quality assurance - quality control (QA/QC) of AMS deployed in the field. These requirements are necessary to ensure that uncertainties of measured concentrations are kept within the required limits during extended periods of continuous monitoring in the field, and include procedures for maintenance, calibration and control checks. Additional procedures are described that determine whether an instrument's equivalence to the reference method is maintained through possible pollution climate changes, over periods longer than five years.
Lastly, this standard describes requirements and procedures for the treatment and validation of raw measurement data that are to be used for the assembly of daily or yearly average concentration values. Experiences with existing methods for data treatment and validation - for similar AMS - have learnt that the different ways of data treatment and validation applied may lead to significant differences in reported results for similar datasets.
When the standard is used for other purposes than the EU Directive, the range and uncertainty requirements may not apply.
This standard contains information for different groups of users. Clauses 5 and 6 and Annex A contain general information about the principles of automated continuous measurement systems for particulate matter, and relevant equipment.
Clause 7 and Annexes B and C are specifically directed towards test houses and laboratories that perform type-approval testing of automated continuous measurement systems for particulate matter. These clauses contain information about:
- type-approval test conditions, test procedures and test requirements,
- system performance requirements,
- evaluation of the type-approval test results,
- evaluation of the uncertainty of the measurement results of the automated continuous measurement systems for particulate matter based on the type-approval test results.
Clauses 8 to 11 are directed towards monitoring networks performing the practical measurements of particulate matter in ambient air. These clauses contain information about:
- initial installation of the system in the monitoring network and acceptance testing,
- ongoing quality assurance/quality control,
- verification of equivalence,
- treatment, validation and reporting of measurement results.

This European Standard specifies a method for the determination of the mass concentration of water soluble NO3- (nitrate), SO42- (sulphate), Cl- (chloride), NH4+ (ammonium), Na+ (sodium), K+ (potassium), Mg2+ (magnesium), Ca2+ (calcium) in PM2,5 as deposited on filters.
This European Standard describes the analytical procedures for determining anions and cations as part of the PM2,5 particulate phase, sample extraction and analysis of anions and cations by ion chromatography. Sampling onto filters will be done in accordance with EN 12341 for PM2,5.
NOTE 1   Alternatively, cations, excluding ammonium, can be analysed by inductively coupled plasma optical emission spectrometry (ICP-OES). Ammonium can also be analysed by photometry or conductometry.
This European Standard can be used for the measurements of anions and cations as required by Directive 2008/50/EC. The method does not take into account the possible losses during sampling due to evaporation.
NOTE 2   NO3-, Cl-, NH4+ are part of the volatile fraction of PM2,5, and the concentrations determined using this standard can be used as minimum values for the concentrations of these ions in PM2,5. NO3-, NH4+, Cl- are usually up to 30 % underestimated due to evaporational losses from the filter during sampling.
This European Standard may be used at rural and urban background sites and road sites that are in accordance with the siting criteria of Directive 2008/50/EC.
This European Standard is applicable to the measurement of anion/cations in PM2,5 samples corresponding to PM2,5 mass concentrations between approximately 1 μg/m3 (i.e. the limit of detection of the standard measurement method (EN 12341) expressed as its uncertainty) up to 120 μg/m3.
The validated range of the anion and cation concentrations based on the field validation measurements is presented in Table 1.
(...)
See Annex A for the statistical analysis of the field validation measurements.

In order to be in compliance with EU Air Quality Directive requirements, the reference methods given in the Directive 2008/50/EC [1] for the measurement of mass concentrations of particulate matter are not commonly used for operation in routine monitoring networks. These networks usually apply automated continuous measurement systems (AMS), such as those based on the use of oscillating microbalances, ß-ray attenuation, or in-situ optical methods. Such AMS are typically capable of producing 24-hour average measurement values over a measurement range up to 1 000 µg/m3 and 1-hour average measurement values up to 10 000 µg/m3, if applicable, where the volume of air is the volume at ambient conditions near the inlet at the time of sampling.
The 1-hour average values may be used for:
a)   direct information of the public;
b)   aggregation to produce daily or yearly average concentration values for regulatory reporting purposes.
Directive 2008/50/EC allows the use of such systems after demonstration of equivalence with the reference method, i.e. after demonstration that these systems meet the Data Quality Objectives for continuous measurements. Guidelines for the demonstration of equivalence are given in Reference [2].
This European Standard lays down the minimum performance requirements and test procedures for the type approval of appropriate AMS for particulate matter. This includes the evaluation of its equivalence with the reference method as laid down in Directive 2008/50/EC.
Further, this European Standard describes minimum requirements for ongoing quality assurance – quality control (QA/QC) of AMS deployed in the field. These requirements are necessary to ensure that uncertainties of measured concentrations are kept within the required limits during extended periods of continuous monitoring in the field, and include procedures for maintenance, calibration and control checks.
Additional procedures are described that determine whether an instrument’s equivalence to the reference method is maintained through possible pollution climate changes, over periods longer than five years.
Lastly, this European Standard describes harmonized requirements and procedures for the treatment and validation of raw measurement data that are used for the assembly of daily or yearly average concentration values. Experience with existing methods for data treatment and validation – for similar AMS – has shown that the different ways of data treatment and validation applied may lead to significant differences in reported results for similar datasets [3].
When the European Standard is used for purposes other than measurements required by Directive 2008/50/EC, the range and uncertainty requirements may not apply.
This European Standard contains information for different groups of users.
Clauses 5 and 6 and Annex A contain general information about the principles of automated continuous measurement systems for particulate matter, and relevant equipment.
Clause 7 and Annexes B and C are specifically directed towards test houses and laboratories that perform type-approval testing of automated continuous measurement systems for particulate matter. These clauses contain information about:
c)   type-approval test conditions, test procedures and test requirements;
d)   system performance requirements;
e)   evaluation of the type-approval test results;
f)   evaluation of the uncertainty of the measurement results of the automated continuous measurement systems for particulate matter based on the type-approval test results.
Clauses 8 to 11 are aimed at monitoring networks performing the practical measurements of particulate matter in ambient air. These clauses contain information about:
g)   initial installation of the system in the monitoring network and acceptance testing;
h)   ongoing quality assurance/quality control;
i)   on-going verification of suitability;
j)   treatment, validation and reporting of measurement results.

This European Standard gives guidance on the measurement of elemental carbon (EC) and organic carbon (OC) following the requirement for the networks of all EU member states to measure EC and OC in particulate matter from June 2010 at background sites according to the Council Directive 2008/50/EC on ambient air quality and cleaner air for Europe [1].
This European Standard describes the analytical procedures for determining EC and OC on quartz fibre filters as μg/cm2, and the subsequent calculation of concentrations as µg/m3. Sampling onto filters is to be done in accordance with EN 12341:2014 for PM2,5. The sampling process determines the size fraction of the particulate matter, the retention of semi-volatile material, and uptake/loss of volatile organic compounds on the filter at the time of sampling.
The same analysis method may also be used for smaller size fractions than PM2,5. Any possible additional artefacts for larger particles, e.g. pyrolysis or higher concentrations of carbonates, should be assessed.
The scope includes rural background, urban background, road side and industrial measurement sites, to allow the assessment of additional exposure of people in urban areas as stated in the objectives of the council directive and to achieve coherence in the European approach.
The applicable concentration range of the proposed method is limited by the optical correction and instrument applied in the analysis of EC and OC. This method was validated from 0,2 µg CEC/cm² and 1,8 µg COC/cm² to 38 µg CEC/cm² and 49 µg COC/cm² in the laboratory and to 16 µg CEC/cm² and 45 µg COC/cm² in the field.

This part of EN 14662 is in accordance with the generic methodology selected as the basis of the European Union Reference Method for the determination of benzene in ambient air [1] for the purpose of comparison of measurement results with limit values with a one-year reference period.
The standard describes guidelines for measurements with, and type approval of, automated gas chromatographs. The use of automated instruments gives this part a different structure compared to the other parts including the procedure for selecting an appropriate automated gas chromatograph by means of type approval tests.
Requirements for use in the field are also described.
The standard is applicable to measurements of airborne benzene vapour in the concentration range from 0 µg/m3 to 50 µg/m3 (Standardised to 101,3 kPa and 293 K). This concentration range represents the certification range for benzene in the type approval test.

This European Standard specifies a semi-continuous measurement method for the determination of the concentration of benzene present in ambient air based on automated sampling and analysis by gas chromatography. This standard describes the performance characteristics and sets the relevant minimum criteria required to select an appropriate automated gas chromatograph (GC) by means of type approval tests. It also includes the evaluation of the suitability of an analyser for use in a specific fixed site so as to meet the data quality requirements as specified in Annex I of Directive 2008/50/EC [1] and requirements during sampling, calibration and quality assurance for use.
The method is applicable to the determination of the mass con¬centration of benzene present in ambient air in the range up to 50 µg/m3 benzene. This concentration range represents the certification range for the type approval test.
Other ranges may be used depending on the levels present in ambient air.
NOTE 1   When the standard is used for other purposes than for measurements required by Directive 2008/50/EC, the ranges and uncertainty requirements may not apply.
The method covers the determination of ambient air concentrations of benzene in zones classified as rural areas, urban-background areas and traffic-orientated locations and locations influenced by industrial sources.
The results are expressed in µg/m3 (at 20 °C and 101,3 kPa).
NOTE 2   50 µg/m3 of benzene corresponds to 15,4 nmol/mol of benzene.
This European Standard contains information for different groups of users.
Clauses 5 to 7 and Annexes C and D contain general information about the principles of benzene measurement by automated gas chromatography and sampling equipment.
Clause 8 and Annex E are specifically directed towards test houses and laboratories that perform type-approval testing of benzene analysers. These sections contain information about:
-   type-approval test conditions, test procedures and test requirements;
-   analyser performance requirements;
-   evaluation of the type-approval test results;
-   evaluation of the uncertainty of the measurement results of the benzene analyser based on the type-approval test results.
Clauses 9 to 11 and Annex F are directed towards monitoring networks performing the practical measurements of benzene in ambient air. These sections contain information about:
-   initial installation of the analyser in the monitoring network and acceptance testing;
-   ongoing quality assurance/quality control;
-   calculation and reporting of measurement results;
-   evaluation of the uncertainty of measurement results under practical monitoring conditions.

EN 12341 describes a standard method for determining the PM10 or PM2,5 mass concentrations of suspended particulate matter in ambient air by sampling the particulate matter on filters and weighing them by means of a balance. Measurements are performed with samplers with inlet designs as specified in Annex A, operating at a nominal flow rate of 2,3 m3/h, over a nominal sampling period of 24 h. Measurement results are expressed in μg/m3, where the volume of air is the volume at ambient conditions near the inlet at the time of sampling. The range of application of this European Standard is from approximately 1 μg/m3 (i.e. the limit of detection of the standard measurement method expressed as its uncertainty) up to 150 μg/m3 for PM10 and 120 μg/m3 for PM2,5. This European Standard describes procedures and gives requirements for the use of so-called sequential samplers, equipped with a filter changer, suitable for extended stand-alone operation. Sequential samplers are commonly used throughout the European Union for the measurement of concentrations in ambient air of PM10 or PM2,5. However, this European Standard does not exclude the use of single-filter samplers.

This European Standard describes a standard method for determining the PM10 or PM2,5 mass concentrations of suspended particulate matter in ambient air by sampling the particulate matter on filters and weighing them by means of a balance.
Measurements are performed with samplers with inlet designs as specified in Annex A, operating at a nominal flow rate of 2,3 m3/h, over a nominal sampling period of 24 h. Measurement results are expressed in µg/m3, where the volume of air is the volume at ambient conditions near the inlet at the time of sampling.
The range of application of this European Standard is from approximately 1 µg/m3 (i.e. the limit of detection of the standard measurement method expressed as its uncertainty) up to 150 µg/m3 for PM10 and 120 µg/m3 for PM2,5.
NOTE 1   Although the European Standard is not validated for higher concentrations, its range of application could well be extended to ambient air concentrations up to circa 200 µg/m3 when using suitable filter materials (see 5.1.4).
This European Standard describes procedures and gives requirements for the use of so-called sequential samplers, equipped with a filter changer, suitable for extended stand-alone operation. Sequential samplers are commonly used throughout the European Union for the measurement of concentrations in ambient air of PM10 or PM2,5. However, this European Standard does not exclude the use of single-filter samplers.
This European Standard does not give procedures for the demonstration of equivalence of other sampler types, e.g. equipped with a different aerosol classifier and/or operating at different flow rates. Such procedures and requirements are given in detail in the Guide to the Demonstration of Equivalence of Ambient Air Monitoring Methods [11] and for automated continuous PM monitors (see CEN/TS 16450:2013).
The present European Standard represents an evolution of earlier European Standards (EN 12341:1998 and EN 14907:2005) through the development of the 2,3 m3/h sampler to include constraints on the filter temperature during and after sampling and the ability to monitor temperatures at critical points in the sampling system. It is recommended that when equipment is procured it complies fully with the present European Standard. However, older versions of these 2,3 m3/h samplers that do not employ sheath air cooling, the ability to cool filters after sampling, or the ability to monitor temperatures at critical points in the sampling system have a special status in terms of their use as reference samplers. Historical results obtained using these samplers will remain valid. These samplers can still be used for monitoring purposes and for equivalence trials, provided that a well justified additional allowance is made to their uncertainties (see Annex B).
In addition, three specific sampling systems  - the -long nozzle - 2,3 m3/h sampler and the 68 m3/h sampler for PM10 in EN 12341:1998, and the 30 m3/h PM2,5 inlet in EN 14907:2005  - also have a special status in terms of their use as reference samplers. Historical results obtained using these samplers will remain valid. These samplers can still be used for monitoring purposes and for equivalence trials, provided that a well-justified additional allowance is made to their uncertainties (see Annex B).
Other sampling systems, as described in Annex B of this European Standard, can be used provided that a well justified additional allowance is made to their uncertainties as derived from equivalence tests.
NOTE 2   By evaluating existing data it has been shown that these samplers give results for PM10 and PM2,5 that are equivalent to those obtained by application of this European Standard. Results are shown in Annex B.
This European Standard also provides guidance for the selection and testing of filters with the aim of reducing the measurement uncertainty of the results obtained when applying this European Standard.

The European Directive on ambient air quality and cleaner air for Europe (2008/50/EC; AQD) identifies different uses for modelling: Assessment, planning, forecast and source apportionment (SA). This document addresses source apportionment modelling and specifies performance tests to check whether given criteria for receptor oriented source apportionment models (RM) are met. The scope of the tests set out in this document is the performance assessment of SA of particulate matter using RM in the context of the European Directives 2004/107/EC and AQD, including the Commission Implementing Decision 2011/850/EU of 12 December 2011. The application of RM does not quantify the spatial origin of particulate matter; hence, this document does not test spatial SA.
This document addresses RM users: practitioners of individual source apportionment studies as well as participants and organizers of source apportionment intercomparison studies. This document is suitable for the evaluation of results of a specific SA modelling system with respect to reference values (a priori known or calculated on the basis of intercomparison participants' values) in the following application areas:
-   Assessment of performance and uncertainties of a modelling system or modelling system set up using the indicators laid down in this document.
-   Testing and comparing different source apportionment outputs in a specific situation (applying an evaluation data set) using the indicators laid down in this document.
-   QA/QC tests every time practitioners run a modelling system.
It should be noted for clarity that the procedures and calculations presented in this document cannot be used to check the performance of a specific SA modelling result without having any a priori reference information about the contributions of sources/source categories.
NOTE   The application of this document implies that the intercomparison is organized and coordinated by an institution with the necessary technical capabilities and independence; the definition of which is beyond the scope of this document.
The principles of RM are summarized in Annex A. An overview of uncertainty sources and recommendations about steps to follow in SA studies are provided in Annex B and Annex C. For further information about SA methodologies, refer to e.g. [1; 2; 3].
There are methodologies different from RM which are widely used to accomplish SA, e.g. source oriented models. These other methodologies cover aspects of SA which are required in the AQD and are not addressed by RM (e.g. allocation of pollutants to geographic emission areas). Performance assessment of such methodologies is out of the scope of this document.

This document describes procedures to assess the applicability of the standard method EN 16909 (determination of OC and EC deposited on filters) to particle size fractions up to 10 µm in aerodynamic diameter (50 % cut off).

This Technical Specification (TS) describes the general principles, including testing procedures and requirements, for the evaluation of performances of low-cost sensor systems for the monitoring of gaseous compounds in ambient air at fixed sites. The evaluation of sensor systems includes tests that shall be performed under prescribed laboratory and/or field conditions.
This TS is not intended for the test of sensors systems used for mobile devices, for the testing of networks of sensor nodes, or for indoor air monitoring although their potential importance is recognized and they could be the subjects of future TS documents.
Low-cost sensors are based on several principles of operations, e. g. amperometric sensors, metal oxides, optical sensors (Infra-Red absorption) etc. However, sensors share some common features, regarding their portability and low-cost compared to traditional reference methods. Typically, sensors are able to continuously monitor air pollution, with low response time ranging between a few tens of seconds and a few minutes.
The described procedure is applicable to the determination of the mass concentration of air pollutants. The pollutants that are considered in this TS consists of:
-the gaseous pollutants regulated under Directives 2008/50/EC: O3, NO2 and NO, CO, SO2 and benzene, in the range of concentrations expected in outdoor ambient air;
-CO2 as proxy for activities involving combustion processes or for CO2 evaporation from soil or water.
When applying the current Technical Specifications, the evaluation of sensors considers the thresholds, limits and averaging times that are defined into the Air Quality Directive (2008/50/EC)[1]. Generally, the Directive sets Limit Values consists of an annual average that is computed by averaging hourly values. For sensors, it can be useful to select shorter averaging time.
In order to rely on the results of tests this protocol, future users shall make sure that sensors will be implemented with the same configuration as the sensor submitted to this protocol. This can include: the same power supply, data acquisition, data processing, identical sampling/ protective box and periodicity of calibration. The sensor shall be submitted to the same regime of QA/QC and maintenance operation as during tests. In addition, it is strongly recommended that sensors measurements are periodically compared side-by-side with the reference method.
For the purpose of this technical specification sensor systems are significantly less expensive than reference methods for the same pollutant.

This Technical Specification (TS) describes the general principles, including testing procedures and requirements, for the evaluation of performances of low-cost sensor systems for the monitoring of gaseous compounds in ambient air at fixed sites. The evaluation of sensor systems includes tests that shall be performed under prescribed laboratory and/or field conditions.
This TS is not intended for the test of sensors systems used for mobile devices, for the testing of networks of sensor nodes, or for indoor air monitoring although their potential importance is recognized and they could be the subjects of future TS documents.
Low-cost sensors are based on several principles of operations, e. g. amperometric sensors, metal oxides, optical sensors (Infra-Red absorption) etc. However, sensors share some common features, regarding their portability and low-cost compared to traditional reference methods. Typically, sensors are able to continuously monitor air pollution, with low response time ranging between a few tens of seconds and a few minutes.
The described procedure is applicable to the determination of the mass concentration of air pollutants. The pollutants that are considered in this TS consists of:
-the gaseous pollutants regulated under Directives 2008/50/EC: O3, NO2 and NO, CO, SO2 and benzene, in the range of concentrations expected in outdoor ambient air;
-CO2 as proxy for activities involving combustion processes or for CO2 evaporation from soil or water.
When applying the current Technical Specifications, the evaluation of sensors considers the thresholds, limits and averaging times that are defined into the Air Quality Directive (2008/50/EC)[1]. Generally, the Directive sets Limit Values consists of an annual average that is computed by averaging hourly values. For sensors, it can be useful to select shorter averaging time.
In order to rely on the results of tests this protocol, future users shall make sure that sensors will be implemented with the same configuration as the sensor submitted to this protocol. This can include: the same power supply, data acquisition, data processing, identical sampling/ protective box and periodicity of calibration. The sensor shall be submitted to the same regime of QA/QC and maintenance operation as during tests. In addition, it is strongly recommended that sensors measurements are periodically compared side-by-side with the reference method.
For the purpose of this technical specification sensor systems are significantly less expensive than reference methods for the same pollutant.