Explanatory Memorandum to COM(1997)500 - Limit values for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air - Main contents
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| dossier | COM(1997)500 - Limit values for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air. |
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| source | COM(1997)500  |
| date | 08-10-1997 |
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51997PC0500
Proposal for a Council Directive relating to limit values for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air /* COM/97/0500 final - SYN 97/0266 */
Official Journal C 009 , 14/01/1998 P. 0006
Proposal for a Council Directive relating to limit values for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (98/C 9/05) (Text with EEA relevance) COM(97) 500 final - 97/0266(SYN)
(Submitted by the Commission on 21 November 1997)
THE COUNCIL OF THE EUROPEAN UNION,
Having regard to the Treaty establishing the European Community,
Having regard to Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management (1), and in particular Article 4 (1) thereof,
Having regard to the proposal from the Commission,
Having regard to the opinion of the Economic and Social Committee,
Acting in accordance with the procedure laid down in Article 189c of the Treaty, in cooperation with the European Parliament,
Whereas, on the basis of principles enshrined in Article 130r of the Treaty, the European Community programme of policy and action in relation to the environment and sustainable development (the fifth environment action programme (2)) envisages in particular amendments to existing legislation on air pollutants; whereas the said programme recommends the establishment of long-term air quality objectives;
Whereas Article 129 of the Treaty provides that health protection requirements are to form a constituent part of the Community's other policies; whereas Article 3 (o) of the Treaty provides that the activities of the Community are to include a contribution to the attainment of a high level of health protection;
Whereas particles which can be inhaled and may penetrate deeply into the lungs are a matter of public health concern; whereas information should be collected on concentrations of particulate matter which may penetrate most deeply into the lung; whereas there is evidence that risks to human health associated with exposure to man-made particulate matter are higher than risks associated with exposure to naturally occurring particles in ambient air; whereas the best means of preventing diseases associated with exposure to man-made particulate matter is to reduce concentrations thereof in ambient air;
Whereas vegetation should be protected against the adverse effects of nitrogen dioxide and of nitric oxide;
Whereas Directive 96/62/EC provides that the numerical limit values and alert thresholds are to be based on the findings of work carried out by international scientific groups active in the field; whereas the Commission is to take account of the most recent scientific research data in the epidemiological and environmental fields concerned and of the most recent advances in metrology for re-examining the elements on which limit values and alert thresholds are based;
Whereas Directive 96/62/EC requires action plans to be developed for zones within which concentrations of pollutants in ambient air exceed limit values plus applicable temporary margins of tolerance in order to ensure compliance with limit values by the date(s) specified; whereas in so far as they relate to particulate matter such action plans and other reduction strategies should aim to reduce concentrations of fine particles as part of the total reduction in concentrations of particulate matter;
Whereas limit values for the protection of ecosystems or vegetation should not apply in the immediate vicinity of agglomerations and other developments;
Whereas standardised accurate measurement techniques are an important element of assessment of ambient air quality;
Whereas up-to-date information on concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air should be readily available to the public;
Whereas Council Directive 80/779/EEC of 15 July 1980 on air quality limit values and guide values for sulphur dioxide and suspended particulates (3), Council Directive 82/884/EEC of 3 December 1982 on a limit value for lead in the air (4) and Council Directive 85/203/EEC of 7 March 1985 on air quality standards for nitrogen dioxide (5); all which Directives, as last amended by the Act of Accession of Austria, Finland and Sweden, should be repealed,
HAS ADOPTED THIS DIRECTIVE:
Contents
- Article 1
- Article 2
- Article 3
- Article 4
- Article 5
- Article 6
- Article 7
- Article 8
- Article 9
- Article 10
- Article 11
- Article 12
- Article 13
- Article 14
- ANNEX I
- II. Alert threshold for sulphur dioxide
- III. Minimum details to be supplied to the public when the alert threshold for sulphur dioxide is exceeded
- ANNEX II
- ANNEX III
- II. PM2,5 action levels for the purposes of Article 5 (4)
- ANNEX IV
- ANNEX V
- II. Determination of exceedance of upper and lower assessment threshold
- ANNEX VI
- I. Macroscale siting
- II. Microscale siting
- III. Documentation and review of site selection
- ANNEX VII
- II. Minimum number of sampling points for continuous measurement to assess compliance with limit values for the protection of ecosystems or other vegetation in zones other than agglomerations
- ANNEX VIII
- II. Results of air quality assessment
- ANNEX IX
- VI. Reference modelling techniques
- ANNEX X
- II. Public information indicators for oxides of nitrogen dioxide
- III. Public information indicators for PM10
- IV. Public information indicator for lead
- V. Public information indicators for PM2,5 for the purposes of Article 5 (4)
- VI. Standardisation
Objectives
The aims of this Directive are:
- to establish limit values and, as appropriate, alert thresholds for concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air designed to avoid, prevent or reduce harmful effects on human health and the environment as a whole,
- to assess concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air on the basis of common methods and criteria,
- to obtain adequate information on concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air and ensure that it is made available to the public,
- to maintain ambient air quality where it is good and improve it in other cases with respect to sulphur dioxide, oxides of nitrogen, particulate matter and lead.
Definitions
The definitions in Article 2 of Directive 96/62/EC shall apply.
For the purposes of this Directive:
1. 'oxides of nitrogen` shall mean nitric oxide and nitrogen dioxide;
2. 'PM10` shall mean particles which pass through a size selective inlet with a 50 % efficiency cut-off at 10 ìm aerodynamic diameter;
3. 'PM2,5` shall mean particles which pass through a size selective inlet with a 50 % efficiency cut-off at 2,5 ìm aerodynamic diameter;
4. 'upper assessment threshold` shall mean the level of pollution referred to in Article 6 (3) of Directive 96/62/EC;
5. 'lower assessment threshold` shall mean the level of pollution referred to in Article 6 (4) of Directive 96/62/EC;
6. 'public information indicator` shall mean a level of pollution such that, if it is exceeded over a given period, this fact shall be recorded in information disseminated pursuant to Article 8 of this Directive.
Sulphur dioxide
1. Member States shall take the necessary measures to ensure that concentrations of sulphur dioxide in ambient air, as assessed in accordance with Article 7, do not exceed the limit values set out in Section I of Annex I as from the dates specified therein.
The margins of tolerance set out in Section I of Annex I shall apply in accordance with Article 8 of Directive 96/62/EC.
2. The alert threshold for concentrations of sulphur dioxide in ambient air is set out in Section II of Annex I. Details supplied to the public in accordance with Article 10 of Directive 96/62/EC shall include as a minimum the items listed in Section III of Annex I.
3. Member States shall record data on concentrations of sulphur dioxide averaged over 10 minutes from measuring stations at which hourly concentrations are measured. Member States shall report to the Commission the 98th and 99th percentile of 10-minute concentrations measured within the calendar year at the same time as data is supplied on hourly concentrations.
Oxides of nitrogen
Member States shall take the necessary measures to ensure that concentrations of nitrogen dioxide, and where applicable of nitrogen dioxide plus nitric oxide, in ambient air, as assessed in accordance with Article 7, do not exceed the limit values set out in Section I of Annex II as from the dates specified therein.
The margins of tolerance set out in Section I of Annex II shall apply in accordance with Article 8 of Directive 96/62/EC.
Particulate matter
1. Member States shall take the necessary measures to ensure that concentrations of PM10 in ambient air, as assessed in accordance with Article 7, do not exceed the limit values set out in Section I of Annex III as from the dates specified therein.
The margins of tolerance set out in Section I of Annex III shall apply in accordance with Article 8 of Directive 96/62/EC.
2. Member States shall install and operate measuring stations to supply data on concentrations of PM2,5. Where possible sampling points should be collocated with sampling points for PM10. The number and the siting of stations at which PM2,5 is measured shall be chosen by each Member State to be representative of concentrations of PM2,5 at local and regional level within that Member State.
Member States shall forward to the Commission annually, no later than nine months after the end of each year, the arithmetic mean, the median, the 98th percentile and the maximum concentration calculated from measurements of PM2,5 over 24 hours within that year. The 98th percentile shall be calculated according to the procedure set out in Annex I, Section 4, to Council Decision 97/101/EC (6).
3. Action plans for PM10 prepared in accordance with Article 8 of Directive 96/62/EC and general strategies for decreasing concentrations of PM10 shall aim to reduce concentrations of PM2,5 as part of the total reduction.
4. Exceptionally, Member States may designate zones or agglomerations within which limit values for PM10 are exceeded owing to significant concentrations of particulate matter in ambient air due to natural sources. Member States shall end to the Commission a first list of any such zones or agglomerations together with information on concentrations and sources of PM10 and PM2,5 therein within two years of the entry into force of this Directive.
Within such zones or agglomerations Member States shall apply the action levels and margins of tolerance for PM2,5 set out in Section II of Annex III in place of the limit values and margins of tolerance for PM10 in determining whether action plans should be prepared in accordance with Article 8 of Directive 96/62/EC. The action levels for PM2,5 shall be used as indicative targets, to be met as far as possible by the relevant attainment date.
Within such zones or agglomerations the upper and lower assessment thresholds for PM10 set out in Section I of Annex V shall determine assessment requirements. Continuous measurement stations for particulate matter shall measure PM10 and PM2,5.
Within such zones or agglomerations information shall be supplied to the public on concentrations of PM2,5 instead of concentrations of PM10.
Lead
Member States shall take the necessary measures to ensure that concentrations of lead in ambient air, as assessed in accordance with Article 7, do not exceed the limit values set out in Section I of Annex IV as from the dates specified therein.
The margins of tolerance set out in Section I of Annex IV shall apply in accordance with Article 8 of Directive 96/62/EC.
Assessment of concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air
1. Upper and lower assessment thresholds for sulphur dioxide, particulate matter and lead for the purposes of Article 6 of Directive 96/62/EC are set out in Section I of Annex V.
The classification of each zone or agglomeration for the purposes of the said Article 6 should be reviewed at least every five years in accordance with the procedure set out in Section II of Annex V. Classification should be reviewed earlier in case of significant change to activities relevant to ambient concentrations of sulphur dioxide, nitrogen dioxide or where relevant nitrogen dioxide plus nitric oxide, particulate matter or lead.
2. Annex VI sets out criteria for determining locations of sampling points for the measurement of sulphur dioxide, oxides of nitrogen, particulate matter and lead. Annex VII sets out the minimum number of continuous measurement stations for each relevant pollutant to be installed in each zone or agglomeration within which measurement is required, if measurement is the sole source of data on concentrations within it. The method used to measure each relevant pollutant shall be the reference method specified in accordance with paragraph 4 or a method which can be demonstrated by the Member State concerned to give equivalent results.
3. For zones and agglomerations within which information from continuous measurement stations is supplemented by information from other sources, such as emission inventories, indicative measurement methods and air quality modelling, the number of continuous measuring stations to be installed and the spatial resolution of other techniques shall be sufficient to enable the concentrations of air pollutants to be established at the types of location defined in Section I of Annex VI, within the achievable limits of accuracy set out in the guidelines to be found in Section I of Annex VIII.
4. Reference methods for analysis of sulphur dioxide, oxides of nitrogen and lead, and for sampling of lead, PM10 and PM2,5 are set out in Sections I to V of Annex IX. Section VI of Annex IX sets out reference techniques for air quality modelling.
5. The date by which Member States shall inform the Commission of the methods used for the preliminary assessment of air quality pursuant to Article 11 (1) (d) of Directive 96/62/EC shall be 31 December 1999.
6. Any amendments necessary to adapt this Article and Annexes V to IX to scientific and technical progress shall be adopted in accordance with the procedure set out in Article 12 of Directive 96/62/EC.
Dissemination of information to the public
1. Member States shall take appropriate steps to disseminate up-to-date information on ambient concentrations of sulphur dioxide, oxides of nitrogen, particulate matter and lead to the public by means, for example, of broadcast media, press, information screens or computer network services and by notification of appropriate organisations such as environmental organisations, consumer organisations, organisations representing the interests of sensitive populations and other pertinent health care bodies. A list of the organisations notified shall be sent to the Commission at the same time as information transmitted pursuant to Article 11 of Directive 96/62/EC.
Such information shall indicate exceedances of the public information indicators listed in Sections I to IV of Annex X.
2. The public information indicators of Section V of Annex X shall apply for the purposes of Article 5 (4) above.
3. When making plans or programmes available to the public pursuant to Article 8 (3) of Directive 96/62/EC Member States shall also make them available to appropriate organisations such as environmental organisations, consumer organisations, organisations representing the interests of sensitive populations and other pertinent health care bodies. A list of the organisations notified shall be sent to the Commission at the same time as the plan or programme.
Repeals and transitional arrangements
1. Directive 80/779/EEC shall be repealed as follows:
- Articles 2 (2), 3 (2), 4, 5, 7 (3), 10 (4), 10 (5), 11 to 14, and Annexes II, III Part A and V shall be repealed with effect from 1 January 2000,
- Articles 1, 2 (1), 3 (1), 6, 7 (1), 7 (2), 8, 9, 10 (1), 10 (2), 10 (3), 15 and 16, and Annexes I, III Part B and IV shall be repealed with effect from 1 January 2005.
2. Directive 82/884/EEC shall be repealed as follows:
- Articles 3 (2), 3 (3), 4, 8 to 11 and the Annex shall be repealed with effect from 1 January 2000,
- Articles 1, 2, 3 (1), 5, 6, 7, 12 and 13 shall be repealed with effect from 1 January 2005.
3. Directive 85/203/EEC shall be repealed as follows:
- Articles 3 (2), 4, 6, 7 (3), 10 to 14, and Annexes II, III and IV shall be repealed with effect from 1 January 2000,
- Articles 1, 2, 3 (1), 5, 7 (1), 7 (2), 8, 9, 15 and 16 and Annex I shall be repealed with effect from 1 January 2010.
4. From 1 January 2000 Member States shall employ measurement stations and other methods of air quality assessment conforming to the requirements of this Directive to assess concentrations of sulphur dioxide, oxides of nitrogen and lead in ambient air to obtain data for the purpose of demonstrating compliance with the limit values established by Directive 80/779/EEC, Directive 82/884/EEC and Directive 85/203/EEC until such time as the limit values established by those Directives are repealed.
Report
The Commission shall submit to the European Parliament and the Council not later than 31 December 2003 a report based on experience of the application of this Directive, and in particular on the results of the most recent scientific research concerning the effects on human health of exposure to sulphur dioxide, to different fractions of particulate matter and to lead, and on progress achieved in methods of measuring and otherwise assessing concentrations of particulate matter in ambient air and the deposition of lead on surfaces.
Implementation
1. Member States shall bring into force the laws, regulations and administrative provisions necessary to comply with this Directive by 31 December 1999 at the latest. They shall forthwith inform the Commission thereof.
When Member States adopt these provisions, these shall contain a reference to this Directive or shall be accompanied by such reference at the time of their official publication. The procedure for such reference shall be adopted by Member States.
2. Member States shall communicate to the Commission the text of the main provisions of national law which they adopt in the field covered by this Directive.
Penalties
The Member States shall lay down the system of penalties for infringement of the national provisions adopted pursuant to this Directive and shall take all necessary measures to ensure that they are applied. The penalties thus provided for must be effective, proportionate and dissuasive. The Member States shall notify the relevant provisions to the Commission by 31 December 1999 at the latest and shall notify it of any amendments to them without delay.
Entry into force
This Directive shall enter into force on the 20th day following its publication in the Official Journal of the European Communities.
Addressees
This Directive is addressed to the Member States.
OJ L 296, 21.11.1996, p. 55.
OJ C 138, 17.5.1993, p. 5.
OJ L 229, 30.8.1980, p. 30.
OJ L 378, 31.12.1982, p. 15.
OJ L 87, 27.3.1985, p. 1.
OJ L 35, 5.2.1997, p. 14.
LIMIT VALUES AND ALERT THRESHOLDS FOR SULPHUR DIOXIDE
I. Limit values for sulphur dioxide
Limit values shall be expressed in ìg/m³. The volume must be standardised at the following conditions of temperature and pressure: 293 °K and 101,3 kPa.
>TABLE>
350 ìg/m³ measured over three consecutive hours at locations representative of air quality over at least 100 km² or an entire zone or agglomeration, whichever is smaller.
III. Minimum details to be supplied to the public when the alert threshold for sulphur dioxide is exceeded
Details to be supplied to the public should include as a minimum:
- date, hour and place of the occurrence,
- forecasts:
- change in concentrations (improvement, stabilisation, or deterioration),
- reason for occurrence and expected change,
- geographical area concerned,
- duration,
- type of population potentially sensitive to the occurrence,
- precautions to be taken by the sensitive population concerned.
LIMIT VALUES FOR NITROGEN DIOXIDE AND NITRIC OXIDE
I. Limit values for nitrogen dioxide and nitric oxide
Limit values shall be expressed in ìg/m³. The volume must be standardised at the following conditions of temperature and pressure: 293 °K and 101,3 kPa.
>TABLE>
LIMIT VALUES AND ACTION LEVELS FOR PARTICULATE MATTER
I. Limit values for particulate matter
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TABLE POSITION>
LIMIT VALUE FOR LEAD
I. Limit values for lead
>TABLE>
DETERMINATION OF REQUIREMENTS FOR ASSESSMENT OF CONCENTRATIONS OF SULPHUR DIOXIDE, OXIDES OF NITROGEN, PARTICULATE MATTER AND LEAD IN AMBIENT AIR WITHIN A ZONE OR AGGLOMERATION
I. Upper and lower assessment thresholds
The following upper and lower assessment thresholds shall apply:
(a) sulphur dioxide
>TABLE>
(b) nitrogen dioxide
>TABLE>
(c) particulate matter
The upper and lower assessment thresholds for PM10 are based on the limit values to be met by 1 January 2010.
>TABLE>
(d) lead
>TABLE>
Exceedance of upper and lower assessment thresholds shall be determined on the basis of concentrations during the previous five years where sufficient data are available. An assessment threshold shall be judged to have been exceeded if the total number of exceedances of the numerical concentration of the threshold during those five years exceeds three times the number of exceedances allowed per year.
Where fewer than five years' data is available Member States may combine measurement campaigns of short duration during the period of the year and at locations likely to be typical of the highest pollution levels with results obtained with information from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds.
LOCATION OF SAMPLING POINTS FOR ASSESSMENT OF CONCENTRATIONS OF SULPHUR DIOXIDE, OXIDES OF NITROGEN, PARTICULATE MATTER AND LEAD IN AMBIENT AIR
The following considerations apply to continuous and quasi-continuous measurement.
(a) Protection of human health
Sampling points directed at the protection of human health should be sited:
(i) to provide data on the areas within zones and agglomerations where the highest concentrations occur to which the population is likely to be directly or indirectly exposed for a period which is significant in relation to the averaging period of the limit value(s);
(ii) to provide data on levels in other areas within the zones and agglomerations which are representative of the exposure of the general population, and with provide information for air quality management purposes.
Sampling points should in general be sited to avoid measurement of very small microenvironments in their immediate vicinity.
Sampling points may be representative of similar locations not in their immediate vicinity.
(b) Protection of ecosystems and other vegetation
Sampling points targeted at the protection of ecosystems for other vegetation should be sited to be representative of air quality away from the immediate vicinity of sources such as agglomerations and other built-up areas, industrial installations and roads. As a guideline a sampling point should be sited to be representative of air quality in a surrounding area of at least 1 000 km².
As a minimum the following guidelines should be met as far as practicable:
- the flow around the inlet sampling probe should be unrestricted without any obstructions affecting the air flow in the vicinity of the sampler (normally some metres away from buildings, balconies, trees, and other obstacles and at least 0,5 metres from the nearest building in the case of sampling points representing air quality at the building line),
- in general, the inlet sampling point should be between 1,5 metres (the breathing zone) and 4 metres above the ground. Higher positions (up to 8 metres) may be necessary in some circumstances. Higher siting may also be appropriate if the station is representative of a large area,
- the inlet probe should not be positioned in the very near vicinity of sources in order to avoid direct intake of emissions unmixed with ambient air,
- the sampler's exhaust outlet should be positioned so that recirculation of exhaust air to the sample inlet is avoided,
- traffic-oriented samplers should be at least 25 metres from major junctions and should be no less than 4 metres from the centre of the nearest traffic lane,
- traffic-oriented samplers for the measurement of NO2 should be sited less than 5 metres from the kerbside,
- in built-up areas, traffic-oriented samplers for the measurement of particulate matter or lead should be sited to be representative of air quality close to the building line.
The following factors may also be taken into account:
- interfering sources,
- security,
- access,
- availability of electrical power and telephone communications,
- visibility of the site in relation to its surroundings,
- safety of public and operators,
- the desirability of collocating sampling points for different pollutants,
- planning requirements.
The site selection procedures should be fully documented at the classification stage by such means as compass point photographs of the surrounding and a detailed map. Sites should be reviewed at regular intervals with repeated documentation to ensure that selection criteria remain valid over time.
Member States intending to close or move measurement stations established pursuant to Directives 80/779/EEC, 82/884/EEC and 85/203/EEC for the assessment of concentrations of sulphur dioxide, nitrogen dioxide and lead shall supply information to support this decision to the Commission.
CRITERIA FOR DETERMINING NUMBERS OF SAMPLING POINTS FOR CONTINUOUS MEASUREMENT OF CONCENTRATIONS OF SULPHUR DIOXIDE, OXIDES OF NITROGEN, PARTICULATE MATTER AND LEAD IN AMBIENT AIR
I. Minimum number of sampling points for continuous measurement to assess compliance with limit values for the protection of human health and alert thresholds in zones and agglomerations where continuous measurement is the sole source of information
a) Diffuse sources
>TABLE>
(b) Point sources
For the assessment of pollution in the vicinity of point sources, the number of sampling points for continuous measurement should be calculated taking into account emission densities, the likely distribution patterns of ambient air pollution and potential exposure of the population.
II. Minimum number of sampling points for continuous measurement to assess compliance with limit values for the protection of ecosystems or other vegetation in zones other than agglomerations
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TABLE POSITION>
DATA QUALITY OBJECTIVES AND COMPILATION OF RESULTS OF AIR QUALITY ASSESSMENT
I. Date quality objectives
The following data quality objectives, for required precision and accuracy of assessment methods, and of minimum time coverage and data capture of measurement provided to guide quality assurance programmes.
>TABLE>
The following information should be compiled for zones or agglomerations within which sources other than measurement are employed to supplement information from measurement, or as the sole means of air quality assessment:
- a description of assessment activities carried out,
- specific methods used, with references to descriptions of the method,
- sources of data and information,
- a description of results, including uncertainties and in particular, the extent of any area or, if relevant the length of road within the zone or agglomeration over which concentrations exceed limit value(s), or as may be limit value(s) plus applicable assessment threshold or the lower assessment area,
- for limit values whose object is the protection of human health, the population potentially exposed to concentrations in excess of the limit value.
Where possible Member States should compile maps showing concentration distributions within each zone and agglomeration.
REFERENCE METHODS FOR ASSESSMENT OF CONCENTRATIONS OF SULPHUR DIOXIDE, OXIDES OF NITROGEN, PARTICULATE MATTER AND LEAD
I. Analysis of sulphur dioxide
(Annex V to Council Directive 80/779/EEC of 15 July 1980 on air quality limit values and guide values for sulphur dioxide and suspended particulates)
II. Reference method of analysis of oxides of nitrogen
(Annex IV to Council Directive 85/203/EEC of 7 March 1985 on air quality standards for nitrogen dioxide)
III. Sampling method and reference method of analysing the concentration of lead in air
(Annex to Council Directive 82/884/EEC of 3 December 1982 on lead in ambient air)
IV. Reference method for sampling PM10
The reference method used to sample PM10 shall be the method described in prEN 12341 (1).
V. Reference method for sampling PM2,5
p.m.
p.m.
Air quality - field test procedure to demonstrate reference equivalence of sampling methods for the PM10 fraction of particulate matter.
PUBLIC INFORMATION INDICATORS
I. Public information indicators for sulphur dioxide
>TABLE>
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0,5 ìg/m³ measured over a calendar year
>TABLE>
For sulphur dioxide and oxides of nitrogen the volume must be standardised at the following conditions of temperature and pressure: 293° K and 101,3 kPa