The Air Quality Limit Values Regulations 2003

Made: 13th August 2003

Laid before Parliament: 14th August 2003

Coming into force: 9th September 2003

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Citation, commencement and extent

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Definitions

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Designation of competent authority

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Duty to ensure compliance with limit values

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Target values and long-term objectives for ozone

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Assessment of ambient air quality

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Classification of zones

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Review of classifications

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Method of assessment of ambient air quality

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Action plans

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Action to be taken where limit values are exceeded

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Programmes and measures to address ozone levels

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Consultations with other Member States of the European Union

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Extension of power to give directions relating to air quality

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Zones where the levels are lower than the limit value

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Public information

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Revocations and transitional provisions

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Information requirements

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SCHEDULE 1 — LIMIT VALUES, MARGINS OF TOLERANCE, INFORMATION ANDALERT THRESHOLDS

PART I — Sulphur Dioxide

Limit values for sulphur dioxide

1.1

	Averaging period	Limit value	Margin of tolerance[^f00009]	Date by which limit value is to be met
1 Hourly limit value for the protection of human health	1 hour	350 µg/m³, not to be exceeded more than 24 times a calendar year	60 µg/m³, reducing to 30 µg/m³ on 1st January 2004 and to 0 µg/m³ on 1st January 2005	1st January 2005
2 Daily limit value for the protection of human health	24 hours	125 µg/m³, not to be exceeded more than 3 times a calendar year	None	1st January 2005
3 Limit value for the protection of ecosystems	Calendar year and winter (1st October to 31st March)	20 µg/m³	None	19th July 2001

Alert threshold for sulphur dioxide

1.2

500 µg/m³ measured over three consecutive hours at locations representative of air quality over at least 100 km² or an entire zone, whichever is the smaller.

Minimum details to be made available to the public when the alert threshold for sulphur dioxide is exceeded

1.3

Details to be made available to the public should include at least:

• the date, hour and place of the occurrence and the reasons for the occurrence, where known;

• any forecasts of: changes in concentration (improvement, stabilisation, or deterioration), together with the reasons for those changes, the geographical area concerned, and the duration of the occurrence;

• the type of population potentially sensitive to the occurrence;

• the precautions to be taken by the sensitive population concerned.

PART II — Nitrogen Dioxide (NO2) and Oxides of Nitrogen (NOx)

Limit values for nitrogen dioxide and oxides of nitrogen

1.1

	Averaging period	Limit value	Margin of tolerance	Date by which limit value is to be met
1 Hourly limit value for the protection of human health	1 hour	200 µg/m³ NO₂, not to be exceeded more than 18 times a calendar year	70 µg/m³, reducing on 1st January 2004 and on 1st January of each following year by equal annual amounts to reach 0 µg/m³by 1st January 2010	1st January 2010
2 Annual limit value for the protection of human health	Calendar year	40 µg/m³ NO₂	14 µg/m³, reducing on 1st January 2004 and on 1st January of each following year by equal annual amounts to reach 0 µg/m³ by 1st January 2010	1st January 2010
3 Annual limit value for the protection of vegetation	Calendar year	30 µg/m³ NOx	None	19th July 2001

Alert threshold for nitrogen dioxide

1.2

400 µg/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 the smaller.

Minimum details to be made available to the public when the alert threshold for nitrogen dioxide is exceeded

1.3

Details to be made available to the public should include at least:

• the date, hour and place of the occurrence and the reasons for the occurrence, where known;

• any forecasts of: changes in concentration (improvement, stabilisation, or deterioration), together with the reasons for those changes, the geographical area concerned, and the duration of the occurrence;

• the type of population potentially sensitive to the occurrence;

• the precautions to be taken by the sensitive population concerned.

PART III — Particulate Matter (PM10)

1

24-hour limit value for the protection of human health

2

Annual limit value for the protection of human health

PART IV — Lead

	Averaging period	Limit value	Margin of tolerance	Date by which limit value is to be met
Annual limit value for the protection of human health	Calendar year	0.5 µg/m³	0.2 µg/m³, reducing on 1st January 2004 to 0.1 µg/m³ and on 1st January 2005 to 0 µg/m³	1st January 2005

PART V — Benzene

	Averaging period	Limit value	Margin of tolerance	Date by which limit value is to be met
Limit value for the protection of human health	Calendar year	5 µg/m³	5 µg/m³ reducing on 1st January 2006 and every 12 months thereafter by 1 µg/m³ to reach 0 µg/m³ by 1st January 2010	1st January 2010

PART VI — Carbon Monoxide

	Averaging period	Limit value	Margin of Tolerance	Date by which limit value is to be met
Limit value for the protection of human health	Maximum daily 8-hour mean	10mg/m³	4 mg/m³ reducing on 1st January 2004 to 2 mg/m³, and to 0 mg/m³ on 1st January 2005	1st January 2005

PART VII — Ozone

Information and alert thresholds for ozone

1.1

	Parameter	Threshold
(a) The exceedance of the threshold is to be measured or predicted for three consecutive hours.	(a) The exceedance of the threshold is to be measured or predicted for three consecutive hours.	(a) The exceedance of the threshold is to be measured or predicted for three consecutive hours.
Information threshold	1 hour average	180 µg/m³
Alert threshold	1 hour average [^f01000]	240 µg/m³

Minimum details to be supplied to the public when the information or alert threshold is exceeded or exceedance is predicted

1.2

Details to be supplied to the public on a sufficiently large scale as soon as possible should include—

1

Information on any observed exceedance:

• (a) the location or area of the exceedance;

• (b) the type of threshold exceeded (information threshold or alert threshold);

• (c) the time at which the exceedance began and its duration; and

• (d) the highest 1-hour and 8-hour mean concentration.

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SCHEDULE 2 — TARGET VALUES AND LONG-TERM OBJECTIVES FOR OZONE CONCENTRATIONS IN AMBIENT AIR

PART I — Definitions and interpretation

In this Schedule—

• (a) all values shall be expressed in µg/m³;

• (b) the volume shall be standardised at the following conditions of temperature and pressure: 293K and 101,3kPa;

• (c) the time shall be specified in Central European Time;

• (d) “AOT40” (expressed in (µg/m³) hours) means the sum of the difference between hourly concentrations greater than 80 µg/m³ (which equals 40 parts per billion) and 80 µg/m³ over a given period using only the 1 hour values measured between 8:00 and 20:00 Central European Time each day;

• (e) in order to be valid, the annual data on exceedances used to check compliance with the target values and long-term objectives below must meet the criteria set out in Part II of Schedule 8.

PART II — Target values for ozone

1

Target value for the protection of human health

2

Target value for the protection of vegetation

PART III — Long-term objectives for ozone

1

Long-term objective for the protection of human health

2

Long-term objective for the protection of vegetation

SCHEDULE 3 — UPPER AND LOWER ASSESSMENT THRESHOLDS AND EXCEEDANCES

PART I — Upper and lower assessment thresholds

The following upper and lower assessment thresholds will apply:

	Health protection	Ecosystem protection
Upper assessment threshold	60% of 24-hour limit value (75 µg/m³), not to be exceeded more than 3 times in any calendar year	60% of winter limit value (12 µg/m³)
Lower assessment threshold	40% of 24-hour limit value (50 µg/m³), not to be exceeded more than 3 times in any calendar year	40% of winter limit value (8 µg/m³)
	Hourly limit value for the protection of human health (NO₂)	Annual limit value for the protection of human health (NO₂)
---	---	---
Upper assessment threshold	70% of limit value (140 µg/m³), not to be exceeded more than 18 times in any calendar year	80% of limit value (32 µg/m³)
Lower assessment threshold	50% of limit value (100 µg/m³), not to be exceeded more than 18 times in any calendar year	65% of limit value (26 µg/m³)
	24-hour average	Annual average
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Upper assessment threshold	60% of limit value (30 µg/m³), not to be exceeded more than seven times in any calendar year	70% of limit value (14 µg/m³)
Lower assessment threshold	40% of limit value (20 µg/m³), not to be exceeded more than seven times in any calendar year	50% of limit value (10 µg/m³)
	Annual average
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Upper assessment threshold	70% of limit value (0.35 µg/m³)
Lower assessment threshold	50% of limit value (0.25 µg/m³)
	Annual Average
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Upper assessment threshold	70% of limit value (3.5 µg/m³)
Lower assessment threshold	40% of limit value (2 µg/m³)
	Eight-hour average
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Upper assessment threshold	70% of limit value (7mg/m³)
Lower assessment threshold	50% of limit value (5mg/m³)

PART II — Determination of exceedances of upper and lower assessment thresholds

Exceedances of upper and lower assessment thresholds must be determined on the basis of concentrations during the previous five years where sufficient data are available. An assessment threshold will be deemed to have been exceeded if it has been exceeded during at least three separate years out of the previous five years.

Where fewer than five years' data are available, measurement campaigns of short duration during the period of the year and at locations likely to be typical of the highest pollution levels may be combined with results obtained from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds.

SCHEDULE 4 — LOCATION OF SAMPLING POINTS FOR THE MEASUREMENT OF RELEVANT POLLUTANTS AND OZONE IN AMBIENT AIR

The following considerations will apply to fixed measurement.

PART I — Macroscale Siting

Protection of human health

a

Sampling points directed at the protection of human health should be sited:

• (i) to provide data on the areas within zones 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;

• (ii) to provide data on levels in other areas within the zones which are representative of the exposure of the general population.

Protection of ecosystems and vegetation

b

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PART II — Macroscale Siting: Ozone

Type of station	Objective of measurement	Representativeness[^f01004]	Macroscale siting criteria
(a) Sampling points should also, where possible, be representative of similar locations not in their immediate vicinity. For rural and background stations, consideration should be given, where appropriate, to co-ordination with the monitoring requirements of Commission Regulation 1091/94[^f00010] concerning protection of the Community’s forests against atmospheric pollution.	(a) Sampling points should also, where possible, be representative of similar locations not in their immediate vicinity. For rural and background stations, consideration should be given, where appropriate, to co-ordination with the monitoring requirements of Commission Regulation 1091/94[^f00010] concerning protection of the Community’s forests against atmospheric pollution.	(a) Sampling points should also, where possible, be representative of similar locations not in their immediate vicinity. For rural and background stations, consideration should be given, where appropriate, to co-ordination with the monitoring requirements of Commission Regulation 1091/94[^f00010] concerning protection of the Community’s forests against atmospheric pollution.	(a) Sampling points should also, where possible, be representative of similar locations not in their immediate vicinity. For rural and background stations, consideration should be given, where appropriate, to co-ordination with the monitoring requirements of Commission Regulation 1091/94[^f00010] concerning protection of the Community’s forests against atmospheric pollution.
Urban	Protection of human health: To assess the exposure of the urban population to ozone, i.e. where the population density and ozone concentration are relatively high and representative of the exposure of the general population	A few km²	Away from the influence of local emissions such as traffic, petrol stations etc.; Vented locations where well mixed levels can be measured; Locations such as residential and commercial areas of cities, parks (away from the trees), big streets or squares with very little or no traffic, open areas characteristic of education, sports or recreation facilities
Suburban	Protection of human health and vegetation: To assess the exposure of the population and vegetation located in the outskirts of the agglomeration, where the highest ozone levels, to which the population and vegetation is likely to be directly or indirectly exposed, occur	Some tens of km²	At a certain distance from the area of maximum emissions, downwind following the main wind direction during conditions favourable to ozone formation; Where population, sensitive crops or natural ecosystems located in the outer fringe of an agglomeration are exposed to high ozone levels; Where appropriate, some suburban stations also upwind of the area of maximum emissions, in order to determine the regional background levels of ozone.
Rural	Protection of human health and vegetation: To assess the exposure of population, crops and natural ecosystems to sub-regional scale ozone concentrations	Sub-regional levels (a few km²)	Stations can be located in small settlements and/or areas with natural ecosystems, forests or crops; Representative for ozone away from the influence of immediate local emissions such as industrial installations and roads; At open area sites, but not on higher mountain-tops.
Rural background	Protection of vegetation and human health: To assess the exposure of crops and natural ecosystems to regional-scale ozone concentrations as well as exposure of the populations	Regional/national/continental levels (1,000 to 10,000 km²)	Station located in areas with lower population density, e.g. with natural ecosystems, forests, far removed from urban and industrial areas and away from local emissions; Avoid locations which are subject to locally enhanced formation of near-ground inversion conditions, also summits of higher mountains; Coastal sites with pronounced diurnal wind cycles of local character are not recommended.

PART III — Microscale siting

The following guidelines should be met as far as practicable:

• the flow around the inlet sampling probe should be unrestricted, (and, for ozone sampling, free in an arc of at least 270°) without any obstructions affecting the airflow in the vicinity of the sampler (normally some metres away from buildings, balconies, trees and other obstacles by more than twice the height the obstacle protrudes above the sampler and at least 0.5 m 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 m (the breathing zone) and 4 m above the ground. Higher positions (up to 8 m) may be necessary in some circumstances and in wooded areas. Higher siting may also be appropriate if the station is representative of a large area;

• the inlet probe should not be positioned in the immediate vicinity of sources in order to avoid the direct intake of emissions unmixed with ambient air;

• the sampler’s exhaust outlet should be positioned so that recirculation of exhaust air to the sampler inlet is avoided;

• location of traffic-orientated samplers; for all pollutants, such sampling points should be at least 25 m from the edge of major junctions and at least 4 m from the centre of the nearest traffic lane; for nitrogen dioxide and carbon monoxide, inlets should be no more than 5 m from the kerbside; for particulate matter, lead and benzene, inlets should be sited so as to be representative of air quality near to the building line;

• for ozone, the inlet probe should be positioned well away from such sources as furnaces and incineration flues and more than 10m from the nearest road, with distance increasing as a function of traffic intensity.

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 co-locating sampling points for different pollutants;

• lanning requirements.

PART IV — Documentation and review of site selection

The site-selection procedures should be fully documented at the classification stage by such means as compass-point photographs of the surrounding area and a detailed map. Sites should be reviewed at regular intervals with repeated documentation to ensure that selection criteria remain valid over time.

For ozone, this requires screening and monitoring of the monitoring data in the context of the meteorological and photochemical processes affecting the ozone concentrations measured at the respective site.

SCHEDULE 5 — CRITERIA FOR DETERMINING MINIMUM NUMBERS OF SAMPLING POINTS FOR FIXED MEASUREMENT OF CONCENTRATIONS OF RELEVANT POLLUTANTS AND OZONE IN AMBIENT AIR

PART I — Relevant pollutants: minimum number of sampling points for fixed measurement to assess compliance with limit values for the protection of human health and alert thresholds in zones where fixed measurement is the sole source of information

Population of zone (thousands )	If concentrations exceed the upper assessment threshold	If maximum concentrations are between the upper and lower assessment thresholds	For SO₂ and NO₂ in agglomerations where maximum concentrations are below the lower assessment thresholds
0-250	1	1	not applicable
250-499	2	1	1
500-749	2	1	1
750-999	3	1	1
1,000-1,499	4	2	1
1,500-1,999	5	2	1
2,000-2,749	6	3	2
2,750-3,749	7	3	2
3,750-4,749	8	4	2
4,750-5,999	9	4	2
>6,000	10	5	3
	For NO₂ and particulate matter: to include at least one urban- background station and one traffic-orientated station—this requirement shall also apply to benzene and carbon monoxide provided that it does not increase the number of sampling points

(b) Point sources

For the assessment of pollution in the vicinity of point sources, the number of sampling points for fixed measurement should be calculated taking into account emission densities, the likely distribution patterns of ambient-air pollution and the potential exposure of the population.

PART II — Relevant pollutants: minimum number of sampling points for fixed measurements to assess compliance with limit values for the protection of ecosystems or vegetation in zones other than agglomerations

If maximum concentrations exceed the upper assessment threshold	If maximum concentrations are between the upper and lower assessment thresholds
1 station every 20,000 km²	1 station every 40,000 km²

In island zones the number of sampling points for fixed measurement should be calculated taking into account the likely distribution patterns of ambient-air pollution and the potential exposure of ecosystems or vegetation.

PART III — Ozone: minimum number of sampling points for fixed continuous measurement to assess air quality in view of compliance with the target values, long-term objectives and information and alert thresholds where continuous measurement is the sole source of information

Population (× 1,000)	Agglomerations (urban and suburban) (a)	Other zones (suburban and rural) (a)	Rural background
0-250		1	1 station/50,000 km² as an average density over all zones in England (b)
251-500	1	2	“
501-1,000	2	2	“
1,001-1,500	3	3	“
1,501-2,000	3	4	“
2,001-2,750	4	5	“
2,751-3,750	5	6	“
>3,750	1 additional station per 2 million inhabitants	1 additional station per 2 million inhabitants

PART IV — Ozone: minimum number of sampling points for fixed measurements for zones attaining the long-term objectives

The number of sampling points for ozone must, in combination with other means of supplementary assessment such as air quality modelling and co-located nitrogen dioxide measurements, be sufficient to examine the trend of ozone pollution and check compliance with the long-term objectives. The number of stations located in agglomerations and other zones may be reduced to one-third of the number specified in Part III. Where information from fixed measurement stations is the sole source of information, at least one monitoring station should be kept. If, in zones where there is supplementary assessment, the result of this is that a zone has no remaining station, co-ordination with the number of stations in neighbouring zones must ensure adequate assessment of ozone concentrations against long-term objectives. The number of rural background stations should be 1 per 100,000 km².

SCHEDULE 6 — MEASUREMENTS OF OZONE PRECURSOR SUBSTANCES

(a) Objectives

The main objectives of measurements of ozone precursor substances are to analyse any trend in ozone precursors, to check the efficiency of emission reduction strategies, to check the consistency of emission inventories and to help attribute emission sources to pollution concentration.

An additional aim is to support the understanding of ozone formation and precursor dispersion processes, as well as the application of photochemical models.

Substances

Measurements of ozone precursor substances must include at least nitrogen oxides, and appropriate volatile organic compounds (VOC). A list of volatile organic compounds recommended for measurement is given below.

Ethane	1-Butene	Isoprene	Ethyl benzene
Ethylene	trans-2-Butene	n-Hexane	m+p-Xylene
Acetylene	cis-2-Butene	i-Hexane	o-Xylene
Propane	1.3-Butadiene	n-Heptane	1,2,4-Trimeth. benzene
Propene	n-Pentane	n-Octane	1,2,3-Trimeth. benzene
n-Butane	i-Pentane	i-Octane	1,3,5-Trimeth. benzene
i-Butane	1-Pentene	Benzene	Formaldehyde
	2-Pentene	Toluene	Total non-methane hydrocarbons

Reference methods

The reference method for the analysis of oxides of nitrogen shall be ISO 7996:1985, Ambient air—determination of the mass concentrations of nitrogen oxides—chemiluminescence method: see footnote (a) to Part I of Schedule 7.

(b) Siting

Measurements should be taken in particular in urban and suburban areas at any monitoring site set up in accordance with the requirements of the Air Quality Limit Values Regulations 2001 and considered appropriate with regard to the monitoring objectives in this Schedule.

SCHEDULE 7 — DATA-QUALITY OBJECTIVES AND COMPILATION OF RESULTS OF AIR-QUALITY ASSESSMENT

PART I — Relevant pollutants: data-quality objectives

The following data-quality objectives for the required accuracy of assessment methods, of minimum time coverage and of data capture of measurement are laid down to guide quality- assurance programmes.

	Sulphur dioxide, nitrogen dioxide and oxides of nitrogen	Particulate matter and lead
The accuracy of the measurement is defined as laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993)[^f00011] or in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994)[^f00012]. The percentages in the table are given for individual measurements averaged, over the period considered, by the limit value, for a 95% confidence interval (bias + two times the standard deviation). The accuracy for continuous measurements should be interpreted as being applicable in the region of the appropriate limit value. The accuracy for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for particulate matter and lead by methods for which accuracy within the 95% confidence interval with respect to continuous monitoring has been demonstrated to be within 10%. Random sampling must be spread evenly over the year.	The accuracy of the measurement is defined as laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993)[^f00011] or in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994)[^f00012]. The percentages in the table are given for individual measurements averaged, over the period considered, by the limit value, for a 95% confidence interval (bias + two times the standard deviation). The accuracy for continuous measurements should be interpreted as being applicable in the region of the appropriate limit value. The accuracy for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for particulate matter and lead by methods for which accuracy within the 95% confidence interval with respect to continuous monitoring has been demonstrated to be within 10%. Random sampling must be spread evenly over the year.	The accuracy of the measurement is defined as laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993)[^f00011] or in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994)[^f00012]. The percentages in the table are given for individual measurements averaged, over the period considered, by the limit value, for a 95% confidence interval (bias + two times the standard deviation). The accuracy for continuous measurements should be interpreted as being applicable in the region of the appropriate limit value. The accuracy for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for particulate matter and lead by methods for which accuracy within the 95% confidence interval with respect to continuous monitoring has been demonstrated to be within 10%. Random sampling must be spread evenly over the year.
Continuous measurement
Accuracy	15%	25%
Minimum data capture	90%	90%
Indicative measurement
Accuracy	25%	50%
Minimum data capture	90%	90%
Minimum time coverage	14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)	14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)
Modelling
Accuracy:
Hourly averages	50%-60%
Daily averages	50%
Annual averages	30%	50%
Objective estimation
Accuracy:	75%	100%

The following data quality objectives, for allowed uncertainty of assessment methods, of minimum time coverage and of data capture of measurement are provided to guide quality assurance programmes.

	Benzene	Carbon monoxide
The uncertainty (on a 95% confidence interval) of the assessment methods shall be evaluated in accordance with the ‘Guide to the Expression of Uncertainty of Measurements' (ISO 1993)[^f00013] or the methodology of ISO 5725:1994[^f00014]. The percentages for uncertainty in the above table are given for individual measurements averaged over the period considered by the limit value, for a 95% confidence interval. The uncertainty for the fixed measurements should be interpreted as being applicable in the region of the appropriate limit value. The uncertainty for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking into account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for benzene if the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25%. Random sampling must be spread evenly over the year.	The uncertainty (on a 95% confidence interval) of the assessment methods shall be evaluated in accordance with the ‘Guide to the Expression of Uncertainty of Measurements' (ISO 1993)[^f00013] or the methodology of ISO 5725:1994[^f00014]. The percentages for uncertainty in the above table are given for individual measurements averaged over the period considered by the limit value, for a 95% confidence interval. The uncertainty for the fixed measurements should be interpreted as being applicable in the region of the appropriate limit value. The uncertainty for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking into account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for benzene if the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25%. Random sampling must be spread evenly over the year.	The uncertainty (on a 95% confidence interval) of the assessment methods shall be evaluated in accordance with the ‘Guide to the Expression of Uncertainty of Measurements' (ISO 1993)[^f00013] or the methodology of ISO 5725:1994[^f00014]. The percentages for uncertainty in the above table are given for individual measurements averaged over the period considered by the limit value, for a 95% confidence interval. The uncertainty for the fixed measurements should be interpreted as being applicable in the region of the appropriate limit value. The uncertainty for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking into account the timing of the events. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation. The Secretary of State may allow for random measurements to be made instead of continuous measurements for benzene if the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25%. Random sampling must be spread evenly over the year.
Fixed measurements
Uncertainty	25%	15%
Minimum data capture	90%	90%
Minimum time coverage	35% urban background and traffic sites (distributed over the year to be representative of various conditions for climate and traffic)
	90% industrial sites
Indicative measurements
Uncertainty	30%	25%
Minimum data capture	90%	90%
Minimum time coverage	14% (one day’s measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)	14% (one measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)
Modelling
Uncertainty:	—	50%
Eight-hour averages	50%	—
Annual averages
Objective estimation
Uncertainty	100%	75%

PART II — Relevant pollutants: results of air quality assessment

The following information should be compiled for zones 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;

• the specific methods used, with references to descriptions of the method;

• the sources of data and information;

• a description of results, including accuracies and, in particular, the extent of any area or, if relevant, the length of road within the zone over which concentrations exceed the limit value or, as may be, the limit value plus applicable margin of tolerance and of any area within which concentrations exceed the upper assessment threshold or the lower assessment threshold;

• for limit values the object of which is the protection of human health, the population potentially exposed to concentrations in excess of the limit value.

Where possible maps shall be compiled showing concentration distributions within each zone.

PART III — Ozone and ozone precursors: data quality objectives

The following data quality objectives, for allowed uncertainty of assessment methods, and of minimum time coverage and of data capture of measurement, are provided to guide quality-assurance programmes.

	For ozone, NO and NO₂
The uncertainty (on a 95% confidence interval) of the measurement methods shall be evaluated in accordance with the principles laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993)[^f00015] of the methodology in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994)[^f00016] or equivalent. The percentages for uncertainty in the table are given for individual measurements, averaged over the period for calculating target values and long-term objectives, for a 95% confidence interval. The uncertainty for continuous fixed measurements should be interpreted as being applicable in the region of the concentration used for the appropriate threshold. The uncertainty for modelling and objective estimation means the maximum deviation of the measured and calculated concentration levels, over the period for calculating the appropriate threshold, without taking into account the timing of events. ‘Time coverage’ means the percentage of time considered for settling the threshold value during which the pollutant is measured. ‘Data capture’ means the ratio of the time for which the instrument produces valid data, to the time for which the statistical parameter or aggregated value is to be calculated. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or normal maintenance of the instrumentation.	The uncertainty (on a 95% confidence interval) of the measurement methods shall be evaluated in accordance with the principles laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993)[^f00015] of the methodology in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994)[^f00016] or equivalent. The percentages for uncertainty in the table are given for individual measurements, averaged over the period for calculating target values and long-term objectives, for a 95% confidence interval. The uncertainty for continuous fixed measurements should be interpreted as being applicable in the region of the concentration used for the appropriate threshold. The uncertainty for modelling and objective estimation means the maximum deviation of the measured and calculated concentration levels, over the period for calculating the appropriate threshold, without taking into account the timing of events. ‘Time coverage’ means the percentage of time considered for settling the threshold value during which the pollutant is measured. ‘Data capture’ means the ratio of the time for which the instrument produces valid data, to the time for which the statistical parameter or aggregated value is to be calculated. The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or normal maintenance of the instrumentation.
Continuous fixed measurement
Uncertainty of individual measurements	15%
Minimum data capture	90% during summer 75% during winter
Indicative measurement
Uncertainty of individual measurements	30%
Minimum data capture	90%
Minimum time coverage	>10% during summer
Modelling
Uncertainty	50%
1 hour averages (daytime)	50%
8 hours daily maximum
Objective estimation
Uncertainty	75%

PART IV — Ozone and ozone precursors: results of air quality assessment

The following information should be compiled for zones within which sources other than measurements are employed to supplement information from measurement:

• a description of the 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 within the zone over which concentrations exceed long-term objectives or target values;

• for long-term objectives or target values whose object is the protection of human health, the population potentially exposed to concentrations in excess of the threshold.

The Secretary of State shall ensure that maps are compiled showing concentration distributions within each zone.

SCHEDULE 8 — REFERENCE METHODS FOR ASSESSMENT OF CONCENTRATIONS OF RELEVANT POLLUTANTS AND OZONE

PART I — Reference method for the analysis of sulphur dioxide

ISO/FDIS 10498 (Standard in draft) Ambient air—determination of sulphur dioxide—ultraviolet fluorescence method[^f00017].

PART II — Reference method for the analysis of nitrogen dioxide and oxides of nitrogen

ISO 7996: 1985 Ambient air—determination of the mass concentrations of nitrogen oxides—chemiluminescence method[^f00018].

PART IIIA — Reference method for the sampling of lead

The reference method for the sampling of lead will be that described in the Annex to Directive 82/884/EEC[^f00019] until such time as the limit value in Schedule 1 to these Regulations is to be met, when the reference method will be that for PM₁₀ specified in Part IV of this Schedule.

PART IIIB — Reference method for the analysis of lead

ISO 9855: 1993 Ambient air—Determination of the particulate lead content of aerosols collected in filters. Atomic absorption spectroscopy method[^f00020].

PART IV — Reference method for the sampling and measurement of PM10

The reference method for the sampling and measurement of PM₁₀ will be that described in EN 12341 ‘Air Quality—Field Test Procedure to Demonstrate Reference Equivalence of Sampling Methods for the PM₁₀ fraction of particulate matter’[^f00021]. The measurement principle is based on the collection on a filter of the PM₁₀ fraction of ambient particulate matter and the gravimetric mass determination.

PART V — Reference method for the sampling and analysis of benzene

The reference method for the measurement of benzene will be a pumped sampling method on a sorbent cartridge followed by gas chromatographic determination.

PART VI — Reference method for the analysis of carbon monoxide

The reference method for the measurement of carbon monoxide will be a non-dispersive infra-red spectrometric (NDIR) method.

PART VII — Reference methods for the analysis of ozone and calibration of ozone instruments

The reference method for analysis of ozone shall be the UV photometric method (ISO FDIS 13964 or equivalent).

The reference method for calibration of ozone instruments shall be the Reference UV photometer method (ISO FDIS 13964, VDI 2468, B1.6 or equivalent).

SCHEDULE 9 — INFORMATION TO BE INCLUDED IN THE PLAN OR PROGRAMME FOR IMPROVEMENT OF AIR QUALITY

Localisation of excess pollution

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General information

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Responsible authorities

3

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Nature and assessment of pollution

4

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Origin of pollution

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Analysis of the situation

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Details of those measures or projects for improvement which existed prior to 21st November 1996

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Details of those measures or projects adopted with a view to reducing pollution following 21st November 1996

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Details of the measures or projects planned or being researched for the long term.

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List of the publications, documents, work etc used to supplement information requested in this Schedule.

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SCHEDULE 10 — REVOCATIONS

Regulations revoked	Reference	With effect from
The Air Quality Standards Regulations 1989, insofar as they apply to England:	S.I. 1989/317
Regulation 2(1) (limit values for sulphur dioxide and suspended particulates in the atmosphere)		1st January 2005
Regulation 4(1) (limit value for lead in air)		1st January 2005
Regulation 6 (limit value for nitrogen dioxide in the atmosphere)		1st January 2010
The Ozone Monitoring and Information Regulations	S.I. 1994/440	9th September 2003
The Air Quality Limit Values Regulations 2001	S.I. 2001/2315	9th September 2003
The Air Quality Limit Values (Amendment) Regulations 2002	S.I. 2002/3117	9th September 2003

SCHEDULE 11 — INFORMATION TO BE OBTAINED AND COLLATED ON OZONE CONCENTRATIONS, AND CRITERIA FOR AGGREGATING DATA AND CALCULATING STATISTICAL PARAMETERS

PART I — Information on ozone concentrations

The following information on ozone concentrations shall be obtained and collated—

	Type of station	Level	Averaging/accumulation time	Provisional data for each month from April to September	Report for each year
(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.	(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.	(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.	(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.	(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.	(a) In this Schedule, “AOT40” has the same meaning as in paragraph (d) of Part I to Schedule 2.
(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.	(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.	(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.	(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.	(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.	(b) Maximum daily 8-hour mean. Where they do not do so already, annual reports must also contain— for ozone, nitrogen dioxide, oxides of nitrogen and the sums of ozone and nitrogen dioxide (added as parts per billion and expressed in µg/m³ ozone) the maximum, 99.9th, 98th and 50th percentiles and annual average and number of valid data from hourly series; and the maximum, 98th and 50th percentile and annual average from a series of daily 8-hour ozone maxima. Data submitted in monthly reports are considered provisional and shall be updated where necessary in subsequent submissions.
Information threshold	Any	180µg/m³	1 hour	—for each day with any exceedance: date, total hours of exceedance, maximum 1 hour ozone and related NO₂ values when required—monthly 1 hour maximum ozone	—for each day with any exceedance: date, total hours of exceedance, maximum 1 hour ozone and related NO₂ values, when required
Alert threshold	Any	240µg/m³	1 hour	—for each day with any exceedance: date, total hours of exceedance, maximum 1 hour ozone and related NO₂ values, when required	—for each day with any exceedance: date, total hours of exceedance, maximum 1 hour ozone and related NO₂ values, when required
Health protection	Any	120µg/m³	8 hours	—for each day with any exceedance: date, 8 hours maximum [^f01008]	—for each day with any exceedance: date, 8 hours maximum [^f01008]
Vegetation protection	Suburban, rural, rural background	AOT40 [^f01007] =6,000µg/m³.h	1 hour, accumulated from May to June		Value
Forest protection	Suburban, rural, rural background	AOT40 [^f01007] =20,000µg/m³.h	1 hour, accumulated from April to September		Value
Materials	Any	40 µg/m³	1 year		Value

PART II — Criteria for aggregating data and calculating statistical parameters

In this Part, percentiles are to be calculated using the method specified in Council Decision 97/101/EC establishing a reciprocal exchange of information and data from networks and individual stations measuring ambient air pollution within Member States[^f00022].

The following criteria are to be used for checking validity when aggregating data and calculating statistical parameters—

Parameter	Required proportion of valid data
(a) In cases where all possible measured data are not available, the following factor shall be used to calculate AOT40 values: $AOT40 (estimate)=AOT40 measured×total possible number of hours*number of measured hourly values$ * being the number of hours within the time period of AOT40 definition (that is, 8:00 to 20:00 Central European Time from 1 May to 31 July each year, for vegetation protection and from 1 April to 30 September each year for forest protection).	(a) In cases where all possible measured data are not available, the following factor shall be used to calculate AOT40 values: $AOT40 (estimate)=AOT40 measured×total possible number of hours*number of measured hourly values$ * being the number of hours within the time period of AOT40 definition (that is, 8:00 to 20:00 Central European Time from 1 May to 31 July each year, for vegetation protection and from 1 April to 30 September each year for forest protection).
1 hour values	75% (45 minutes)
8 hour values	75% of values (6 hours)
Maximum daily 8 hours mean from hourly running 8 hours averages	75% of the hourly running 8 hour averages(8 hours per day)
AOT40	90% of the 1 hour values over the time period defined for calculating the AOT40 value [^f01009]
Annual mean	75% of the 1 hour values over summer (April to September) and winter (January to March, October to December) seasons separately
Number of exceedances and maximum values per month	90% of the daily maximum 8 hours mean value (27 available daily values per month) 90% of the 1 hour values between 8:00 and 20:00 Central European Time
Number of exceedances and maximum values per year	Five out of six summer months over the summer season (April to September)

Signed

Elliot Morley — Minister of State, — Department for Environment, Food and Rural Affairs — 2003-08-13

Explanatory note

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Footnotes

[^f00001]: 1972, c. 68.

[^f00002]: S.I. 1988/785.

[^f00003]: OJ No. L 296, 21.11.1996, p. 55.

[^f00004]: See footnote (a) to regulation 3.

[^f00005]: OJ No. L163, 29.6.1999, p. 41.

[^f00006]: OJ No. L313, 13.12.2000, p. 12.

[^f00007]: 1995 c. 25; section 85 was amended by the Greater London Authority Act 1999 (c. 29), section 367.

[^f00008]: OJ No. L 229, 30.8.1980, p. 30.

[^f00009]: The figures for margins of tolerance for each of the relevant pollutants given in this Schedule are calculated from those given in Annexes I to IV of Directive 99/30/EC.

[^f00010]: OJ No. L 125, 18.5.1994, p. 1.

[^f00011]: Copies of these International Standards Organisation publications can be purchased from the British Standards Institution ‘BSI’ sales department either by telephone on 0208-996-9001 or by post from the BSI, Standards House, 389 Chiswick High Road, London W4 4AL.

[^f00012]: Copies of these International Standards Organisation publications can be purchased from the British Standards Institution ‘BSI’ sales department either by telephone on 0208-996-9001 or by post from the BSI, Standards House, 389 Chiswick High Road, London W4 4AL.

[^f00013]: See footnote (a) to Part I of Schedule 7 above for location of ISO publications.

[^f00014]: See footnote (a) to Part I of Schedule 7 above for location of ISO publications.

[^f00015]: Copies of these International Standards Organisation publications can be purchased from the British Standards Institution ‘BSI’ sales department either by telephone on 020-8996-9001 or by post from the BSI, Standards House, 389 Chiswick High Road, London W4 4AL.

[^f00016]: Copies of these International Standards Organisation publications can be purchased from the British Standards Institution ‘BSI’ sales department either by telephone on 020-8996-9001 or by post from the BSI, Standards House, 389 Chiswick High Road, London W4 4AL.

[^f00017]: See footnote (a) to Part I of Schedule 7 above for location of ISO documents.

[^f00018]: See footnote (a) to Part I of Schedule 7 above for location of ISO documents.

[^f00019]: OJ No. L 378, 31.12.1982, p. 15.

[^f00020]: See footnote (a) to Part I of Schedule 7 above for location of ISO documents.

[^f00021]: European Standards Institute ‘CEN’ publication reference BSEN 12341, obtainable from the British Standards Institution: see footnote (a) to Part I of Schedule 7 above.

[^f00022]: OJ No. L035, 5.2.1997, p. 14.

[^f00023]: OJ No. L296, 21.11.1996, p. 55.

[^f00024]: OJ No. L163, 29.6.1999, p. 41, amended by Commission Decision 2001/744/EC, OJ No. L278, 23.10.2001, p. 35.

[^f00025]: OJ No. L313, 13.12.2000, p. 12.

[^f00026]: OJ No. L67, 9.3.2002, p. 14.

[^f00027]: S.I. 2001/2315.

[^f00028]: OJ No. L278, 23.10.2001, p. 35.

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The maximum daily 8-hour mean concentration shall be selected by examining 8-hour running averages, calculated from hourly data and updated each hour. Each 8-hour average so calculated shall be assigned to the day on which it ends, i.e. the first calculation period for any one day shall be the period from 17:00 on the previous day to 01:00 on that day; the last calculation period for any one day shall be the period from 16:00 to 24:00 on that day.

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a

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In this Schedule—

• (a) all values shall be expressed in µg/m³;

• (b) the volume shall be standardised at the following conditions of temperature and pressure: 293K and 101,3kPa;

• (c) the time shall be specified in Central European Time;

• (d) “AOT40” (expressed in (µg/m³) hours) means the sum of the difference between hourly concentrations greater than 80 µg/m³ (which equals 40 parts per billion) and 80 µg/m³ over a given period using only the 1 hour values measured between 8:00 and 20:00 Central European Time each day;

• (e) in order to be valid, the annual data on exceedances used to check compliance with the target values and long-term objectives below must meet the criteria set out in Part II of Schedule 8.

The following upper and lower assessment thresholds will apply:

	Health protection	Ecosystem protection
Upper assessment threshold	60% of 24-hour limit value (75 µg/m³), not to be exceeded more than 3 times in any calendar year	60% of winter limit value (12 µg/m³)
Lower assessment threshold	40% of 24-hour limit value (50 µg/m³), not to be exceeded more than 3 times in any calendar year	40% of winter limit value (8 µg/m³)
	Hourly limit value for the protection of human health (NO₂)	Annual limit value for the protection of human health (NO₂)
---	---	---
Upper assessment threshold	70% of limit value (140 µg/m³), not to be exceeded more than 18 times in any calendar year	80% of limit value (32 µg/m³)
Lower assessment threshold	50% of limit value (100 µg/m³), not to be exceeded more than 18 times in any calendar year	65% of limit value (26 µg/m³)
	24-hour average	Annual average
---	---	---
Upper assessment threshold	60% of limit value (30 µg/m³), not to be exceeded more than seven times in any calendar year	70% of limit value (14 µg/m³)
Lower assessment threshold	40% of limit value (20 µg/m³), not to be exceeded more than seven times in any calendar year	50% of limit value (10 µg/m³)
	Annual average
---	---
Upper assessment threshold	70% of limit value (0.35 µg/m³)
Lower assessment threshold	50% of limit value (0.25 µg/m³)
	Annual Average
---	---
Upper assessment threshold	70% of limit value (3.5 µg/m³)
Lower assessment threshold	40% of limit value (2 µg/m³)
	Eight-hour average
---	---
Upper assessment threshold	70% of limit value (7mg/m³)
Lower assessment threshold	50% of limit value (5mg/m³)

Exceedances of upper and lower assessment thresholds must be determined on the basis of concentrations during the previous five years where sufficient data are available. An assessment threshold will be deemed to have been exceeded if it has been exceeded during at least three separate years out of the previous five years.

Where fewer than five years' data are available, measurement campaigns of short duration during the period of the year and at locations likely to be typical of the highest pollution levels may be combined with results obtained from emission inventories and modelling to determine exceedances of the upper and lower assessment thresholds.

The following considerations will apply to fixed measurement.

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Protection of human health and vegetation:

a

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The following guidelines should be met as far as practicable:

• — the flow around the inlet sampling probe should be unrestricted, (and, for ozone sampling, free in an arc of at least 270°) without any obstructions affecting the airflow in the vicinity of the sampler (normally some metres away from buildings, balconies, trees and other obstacles by more than twice the height the obstacle protrudes above the sampler and at least 0.5 m 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 m (the breathing zone) and 4 m above the ground. Higher positions (up to 8 m) may be necessary in some circumstances and in wooded areas. Higher siting may also be appropriate if the station is representative of a large area;

• — the inlet probe should not be positioned in the immediate vicinity of sources in order to avoid the direct intake of emissions unmixed with ambient air;

• — the sampler’s exhaust outlet should be positioned so that recirculation of exhaust air to the sampler inlet is avoided;

• — location of traffic-orientated samplers;— for all pollutants, such sampling points should be at least 25 m from the edge of major junctions and at least 4 m from the centre of the nearest traffic lane;— for nitrogen dioxide and carbon monoxide, inlets should be no more than 5 m from the kerbside;— for particulate matter, lead and benzene, inlets should be sited so as to be representative of air quality near to the building line;

• — for ozone, the inlet probe should be positioned well away from such sources as furnaces and incineration flues and more than 10m from the nearest road, with distance increasing as a function of traffic intensity.

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 co-locating sampling points for different pollutants;

• — lanning requirements.

The site-selection procedures should be fully documented at the classification stage by such means as compass-point photographs of the surrounding area and a detailed map. Sites should be reviewed at regular intervals with repeated documentation to ensure that selection criteria remain valid over time.

For ozone, this requires screening and monitoring of the monitoring data in the context of the meteorological and photochemical processes affecting the ozone concentrations measured at the respective site.

(b) Point sources

For the assessment of pollution in the vicinity of point sources, the number of sampling points for fixed measurement should be calculated taking into account emission densities, the likely distribution patterns of ambient-air pollution and the potential exposure of the population.

In island zones the number of sampling points for fixed measurement should be calculated taking into account the likely distribution patterns of ambient-air pollution and the potential exposure of ecosystems or vegetation.

a

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b

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The number of sampling points for ozone must, in combination with other means of supplementary assessment such as air quality modelling and co-located nitrogen dioxide measurements, be sufficient to examine the trend of ozone pollution and check compliance with the long-term objectives. The number of stations located in agglomerations and other zones may be reduced to one-third of the number specified in Part III. Where information from fixed measurement stations is the sole source of information, at least one monitoring station should be kept. If, in zones where there is supplementary assessment, the result of this is that a zone has no remaining station, co-ordination with the number of stations in neighbouring zones must ensure adequate assessment of ozone concentrations against long-term objectives. The number of rural background stations should be 1 per 100,000 km².

(a) Objectives

The main objectives of measurements of ozone precursor substances are to analyse any trend in ozone precursors, to check the efficiency of emission reduction strategies, to check the consistency of emission inventories and to help attribute emission sources to pollution concentration.

An additional aim is to support the understanding of ozone formation and precursor dispersion processes, as well as the application of photochemical models.

Measurements of ozone precursor substances must include at least nitrogen oxides, and appropriate volatile organic compounds (VOC). A list of volatile organic compounds recommended for measurement is given below.

Ethane	1-Butene	Isoprene	Ethyl benzene
Ethylene	trans-2-Butene	n-Hexane	m+p-Xylene
Acetylene	cis-2-Butene	i-Hexane	o-Xylene
Propane	1.3-Butadiene	n-Heptane	1,2,4-Trimeth. benzene
Propene	n-Pentane	n-Octane	1,2,3-Trimeth. benzene
n-Butane	i-Pentane	i-Octane	1,3,5-Trimeth. benzene
i-Butane	1-Pentene	Benzene	Formaldehyde
	2-Pentene	Toluene	Total non-methane hydrocarbons

Reference methods

The reference method for the analysis of oxides of nitrogen shall be ISO 7996:1985, Ambient air—determination of the mass concentrations of nitrogen oxides—chemiluminescence method: see footnote (a) to Part I of Schedule 7.

(b) Siting

Measurements should be taken in particular in urban and suburban areas at any monitoring site set up in accordance with the requirements of the Air Quality Limit Values Regulations 2001 and considered appropriate with regard to the monitoring objectives in this Schedule.

The following data-quality objectives for the required accuracy of assessment methods, of minimum time coverage and of data capture of measurement are laid down to guide quality- assurance programmes.

	Sulphur dioxide, nitrogen dioxide and oxides of nitrogen	Particulate matter and lead
Continuous measurement
Accuracy	15%	25%
Minimum data capture	90%	90%
Indicative measurement
Accuracy	25%	50%
Minimum data capture	90%	90%
Minimum time coverage	14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)	14% (One measurement a week at random, evenly distributed over the year, or eight weeks evenly distributed over the year.)
Modelling
Accuracy:
Hourly averages	50%-60%
Daily averages	50%
Annual averages	30%	50%
Objective estimation
Accuracy:	75%	100%

The accuracy of the measurement is defined as laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993) or in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994) . The percentages in the table are given for individual measurements averaged, over the period considered, by the limit value, for a 95% confidence interval (bias + two times the standard deviation). The accuracy for continuous measurements should be interpreted as being applicable in the region of the appropriate limit value.

The accuracy for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking account the timing of the events.

The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation.

The Secretary of State may allow for random measurements to be made instead of continuous measurements for particulate matter and lead by methods for which accuracy within the 95% confidence interval with respect to continuous monitoring has been demonstrated to be within 10%. Random sampling must be spread evenly over the year.

The following data quality objectives, for allowed uncertainty of assessment methods, of minimum time coverage and of data capture of measurement are provided to guide quality assurance programmes.

	Benzene	Carbon monoxide
Fixed measurements
Uncertainty	25%	15%
Minimum data capture	90%	90%
Minimum time coverage	35% urban background and traffic sites (distributed over the year to be representative of various conditions for climate and traffic)
	90% industrial sites
Indicative measurements
Uncertainty	30%	25%
Minimum data capture	90%	90%
Minimum time coverage	14% (one day’s measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)	14% (one measurement a week at random, evenly distributed over the year, or 8 weeks evenly distributed over the year)
Modelling
Uncertainty:		50%
Eight-hour averages	50%
Annual averages
Objective estimation
Uncertainty	100%	75%

The uncertainty (on a 95% confidence interval) of the assessment methods shall be evaluated in accordance with the ‘Guide to the Expression of Uncertainty of Measurements*rsquo; (ISO 1993) or the methodology of ISO 5725:1994 . The percentages for uncertainty in the above table are given for individual measurements averaged over the period considered by the limit value, for a 95% confidence interval. The uncertainty for the fixed measurements should be interpreted as being applicable in the region of the appropriate limit value.

The uncertainty for modelling and objective estimation is defined as the maximum deviation of the measured and calculated concentration levels, over the period considered by the limit value, without taking into account the timing of the events.

The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or the normal maintenance of the instrumentation.

The Secretary of State may allow for random measurements to be made instead of continuous measurements for benzene if the uncertainty, including the uncertainty due to random sampling, meets the quality objective of 25%. Random sampling must be spread evenly over the year.

The following information should be compiled for zones 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;

• — the specific methods used, with references to descriptions of the method;

• — the sources of data and information;

• — a description of results, including accuracies and, in particular, the extent of any area or, if relevant, the length of road within the zone over which concentrations exceed the limit value or, as may be, the limit value plus applicable margin of tolerance and of any area within which concentrations exceed the upper assessment threshold or the lower assessment threshold;

• — for limit values the object of which is the protection of human health, the population potentially exposed to concentrations in excess of the limit value.

Where possible maps shall be compiled showing concentration distributions within each zone.

The following data quality objectives, for allowed uncertainty of assessment methods, and of minimum time coverage and of data capture of measurement, are provided to guide quality-assurance programmes.

	For ozone, NO and NO₂
Continuous fixed measurement
Uncertainty of individual measurements	15%
Minimum data capture	90% during summer75% during winter
Indicative measurement
Uncertainty of individual measurements	30%
Minimum data capture	90%
Minimum time coverage	>10% during summer
Modelling
Uncertainty	50%
1 hour averages (daytime)	50%
8 hours daily maximum
Objective estimation
Uncertainty	75%

The uncertainty (on a 95% confidence interval) of the measurement methods shall be evaluated in accordance with the principles laid down in the ‘Guide to the Expression of Uncertainty of Measurements’ (ISO 1993) of the methodology in ISO 5725-1 ‘Accuracy (trueness and precision) of measurement methods and results’ (ISO 1994) or equivalent. The percentages for uncertainty in the table are given for individual measurements, averaged over the period for calculating target values and long-term objectives, for a 95% confidence interval. The uncertainty for continuous fixed measurements should be interpreted as being applicable in the region of the concentration used for the appropriate threshold.

The uncertainty for modelling and objective estimation means the maximum deviation of the measured and calculated concentration levels, over the period for calculating the appropriate threshold, without taking into account the timing of events.

‘Time coverage’ means the percentage of time considered for settling the threshold value during which the pollutant is measured.

‘Data capture’ means the ratio of the time for which the instrument produces valid data, to the time for which the statistical parameter or aggregated value is to be calculated.

The requirements for minimum data capture and time coverage do not include losses of data due to the regular calibration or normal maintenance of the instrumentation.

The following information should be compiled for zones within which sources other than measurements are employed to supplement information from measurement:

• — a description of the 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 within the zone over which concentrations exceed long-term objectives or target values;

• — for long-term objectives or target values whose object is the protection of human health, the population potentially exposed to concentrations in excess of the threshold.

The Secretary of State shall ensure that maps are compiled showing concentration distributions within each zone.

ISO/FDIS 10498 (Standard in draft) Ambient air—determination of sulphur dioxide—ultraviolet fluorescence method .

ISO 7996: 1985 Ambient air—determination of the mass concentrations of nitrogen oxides—chemiluminescence method .

The reference method for the sampling of lead will be that described in the Annex to Directive 82/884/EEC until such time as the limit value in Schedule 1 to these Regulations is to be met, when the reference method will be that for PM₁₀ specified in Part IV of this Schedule.

ISO 9855: 1993 Ambient air—Determination of the particulate lead content of aerosols collected in filters. Atomic absorption spectroscopy method .