Air Pollution
in the UK:2003

A report prepared by the National Environmental Technology
Centre (Netcen) for the Department for Environment, Food andRural Affairs and the Devolved Administrations.

This page has been left deliberately blank

Air Pollution in the UK: 2003
A report prepared for the Department for Environment, Foodand Rural Affairs, the Welsh Assembly Government, theScottish Executive and the Department of Environment inNorthern IrelandThis report has been compiled by Jon Bower, Paul Willis, Geoff
Broughton, Andrew Kent and Jeff Lampert of Netcen; however, the data
here presented represent the end-product of the efforts of many persons
and organisations in the private sector, local and central government.

November 2004

Front cover image © Jon Bower

Air Pollution in the UK: 2003

Title

Air Pollution in the UK: 2003

Customer

Defra

Confidentiality,
copyright andreproduction

Crown CopyrightFile reference

Netcen/ED45098/Issue 1

Reference number

Netcen/ED45098/Issue 1
Jon Bower
National Environmental Technology Centre
551 Harwell
DidcotOxfordshire OX11 0QJ
England
Telephone +44(0)870 190 6416
Facsimile +44(0)870 190 6607
Netcen is an operating division of
AEA Technology plc
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AuthorsName

Jon Bower, Jeff Lampert, Geoff
Broughton

Reviewed byName

Jon Bower, Paul Willis, Geoff
DollardApproved byName

Jacquie Berry

Date

23 November 2004

Netceni

Air Pollution in the UK: 2003

1. Executive Summary
For those of you short of time…
This is the latest in a long-running series of annual reports summarising measurementsfrom national air pollution monitoring networks operated on behalf of Defra (Department
for Environment, Food and Rural Affairs) and the Devolved Administrations of Scotland,
Wales and Northern Ireland.
It includes data and analyses from the calendar year (January to December) 2003. The
pollutants featured in this report are:Ozone (O3)
Nitrogen oxides (NO and NO2)
Sulphur dioxide (SO2)
Carbon Monoxide (CO)PM10 particles
Benzene1,3-butadiene
Because of their potential impacts on human health, welfare and natural environments,
these pollutants are routinely measured at many locations throughout the UK.
The measurements reported here were made in national automatic air monitoring
networks, comprising 125 stations for the year in question. These networks serve avariety of policy, regulatory, scientific research and public health objectives.
In this report, we:
1. Consider current UK and European efforts to tackle air pollution, identifying thepivotal role of air monitoring in this process
2. Describe current UK air monitoring networks, their objectives and methodologies.
Detailed site maps and site registers are also provided
3. Review current UK Air Quality Objectives and examine how and where these were
exceeded during the year
4. Investigate, using detailed maps, how pollution levels vary across the country
5. Examine major periods of elevated pollution (so called pollution ‘episodes’) thathave occurred recently
6. Assess long-term trends in order to identify how pollution levels in theatmosphere have changed over time
7. Provide in the second half of the report detailed statistical summary tables foreach pollutant
8. Identify other published, web and media sources for information on the UK’s air
quality.
The report therefore provides a comprehensive analytical picture of air pollution in the UK
up to and during 2003.

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Air Pollution in the UK: 2003

CONTENTS
1. Executive Summary
2. Introduction

1

PART 1- Networks and Observations
3. UK and International Policy fortackling air pollution

4

3.1 European background
3.2 The UK perspective
3.3 A local focus

468

4. Where and how air pollution ismeasured in the UK

10

4.1 Role of ambient air quality monitoring
4.2 A brief history of monitoring in the UK
4.3 The current situation
4.4 Emphasis on data quality
4.5 Disseminating and using air quality data

10
11
13
20
21

5. High pollution episodes

27

5.1 A winter smog episode5.2 A Bonfire Night episode5.3 A summer smog episode5.4 An episode involving long-range transport
5.5 An episode involving short-range transport

28
28
30
31
31

6. How air pollution varies acrossthe UK33

7. How air pollution has changed
over time

36

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Air Pollution in the UK: 2003

PART 2- Measurement sites,
instrumentation and statistics
8. Benzene

43

9. 1,3-Butadiene49

10. Carbon Monoxide

55

11.Nitrogen dioxide

65

12. Oxides of nitrogen75

13. PM10 particles

85

14. PM2.5 particles

95

15. Sulphur dioxide

103

16. Ozone

113

PART 3- Appendices1- The Major Air Pollutants measured
in the UK

124

2- Regional Maps of UK Automatic Air
Monitoring Sites

128

3- The UK’s Automatic and Samplerbased Air Monitoring Networks

134

4- Calculation methods, statisticalmethods and measurement uncertainty

142

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Air Pollution in the UK: 2003

2. Introduction
An outline of what’s in this report…

The quality of the air that we breathe can have an important impact on our health andquality of life; it is therefore important to us all. Measuring and understanding air
pollution provides a sound scientific basis for its management and control. Considerable
effort is therefore devoted in the UK to the systematic measurement of levels of air
pollution nationwide. This effort started in earnest following the infamous coal-burning
smogs of the 1950s and 60s, but has expanded massively in scope, coverage andsophistication since then.
Air quality monitoring, and the results presented in this report, should not be seen as an
end in themselves; rather, they offer us the best way of understanding our pollution
problems, so they can be tackled effectively at local, national and international level.
Monitoring air pollution in the UK has the following broad objectives:
To provide a sound scientific basis for the development of cost-effective control
policies and solutions
To assess how far air quality standards and objectives are being met
To evaluate potential impacts on population health and welfare
To determine the impact of air pollution on ecosystems and our naturalenvironment
To provide the public with reliable and up-to-date information on air pollution.
This report aims to provide a simple guide, written as far as possible in non-technicallanguage, to what the latest measurements tell us about air pollution in the UK. The
report comprises two parts. The first part is primarily descriptive and analytical. In it,
we’ll:
Summarise current UK and European policy efforts and initiatives to tackle air
pollution (Section 3)
Review where and how air pollution is measured in this country, examining
monitoring networks, site locations and measurement techniques (Section 4)
Examine key episodes - major periods of elevated pollution that have occurred overrecent years (Section 5)
Investigate through a series of detailed maps how pollution levels vary across the
UK (Section 6)
Assess long-term pollution trends in order to see whether pollution levels are
declining over time (Section 7).
The second part of the report is statistical, providing a detailed pollutant-specificsummary of measurements. From Sections 8 to 16, we provide for each pollutant
measured in the automatic networks:
Information on measurement and calibration techniques, instruments utilised andestimated accuracy and precision
A summary of relevant UK objectives for that pollutant, together with EC Limit
Values and WHO Guidelines
A map of UK national network measurement sites
A detailed statistical summary of the measurements made in 2003
Matching information on exceedences of UK Air Quality Objectives
Time-series graphs showing variations in pollutant concentrations throughout theyear at typical urban, rural and other site types
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Air Pollution in the UK: 2003

Corresponding diurnal graphs showing typical variations in pollutant concentrations
during the day
Long-term time series showing trends in annual average measured concentrations.
In a series of Appendices, we’ll also provide additional background information on themeasured pollutants, together with regional site location maps and details of the different
UK national air monitoring networks.

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Air Pollution in the UK: 2003

Air Pollution in the UK: 2003
Part 1In this part of the report, we describe the reasons formonitoring air quality and examine how the UK networks
have evolved over the years to meet our changing needs andobjectives.
We then review major recent air pollution episodes andassess variations in pollution levels across the country.
Finally, we examine long-term trends in order to see if
pollution is getting worse over time.

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Air Pollution in the UK: 2003

3. UK and International Policy for
Tackling Air Pollution
The policy background to why we monitor air quality…
To understand why and how we measure air pollution in the UK, it’s first necessary toconsider the broader policy and regulatory background to the monitoring, both atnational and international level.
Air pollution is becoming an increasingly important focus of interest for national,
European and international policy makers. This has been triggered, in part, by increasing
evidence that air pollution can pose significant risks to our health and amenity, as well as
threatening our natural environment. In recognition of this, the European Union’s Sixth
Environment Action Programme, "Environment 2010: Our future, Our choice"1, includes
Environment and Health as one of the four main target areas where new effort istargetted, with air pollution identified as one of the priority issues to be tackled. The
need to protect human health and welfare is also a central feature of the UK’s Air Quality
Strategy2, discussed later in this section.
Another factor in the increased attention paid to air pollution is emerging evidence of its
relationship to broader issues of global climate change; recent years have shown thedramatic impacts of a series of unusually hot summers throughout many parts of Europe.
Some of these impacts have been a consequence of elevated levels of air pollution.

3.1 European Background
Air quality is one of the areas in which Europe has been particularly active in recent
years. The European Commission’s aim has been to develop an overall strategy throughthe setting of long-term air quality objectives. Within the European Community, a seriesof air quality Directives and Decisions over the last decade has:Established Limit Values for key air pollutants and defined overall requirements formonitoring progress against these targets
Defined the monitoring, modelling and air quality management obligations ofMember States
Set targets for pollutant emissions in different types of industry as well as in thetransport sector
Confirmed the need to communicate information on air quality to the public atlarge.
In 1996, the Environment Council adopted Framework Directive 96/62/EC3 on ambient
air quality assessment and management. This key Directive revised and harmonised preexisting legislation for a range of air pollutants. It also extended the scope of legislation
to cover an increased range of pollutants, and set a timetable for the development ofDaughter Directives; these have specified the detailed Limit Values, monitoring andassessment methods for sulphur dioxide, nitrogen dioxide, particulate matter, lead,ozone, benzene and carbon monoxide. A proposal for further extending the scope ofpollutants to include polycyclic aromatic hydrocarbons, cadmium, arsenic, nickel andmercury is currently at an advanced stage of consideration.
A list of current EC Directive Limit and Target Values for air pollutants covered by the
Directives is provided in the later, pollutant-specific parts of this report. Further detailed
information on the major sources and impacts of these pollutants is provided in Appendix
1.
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Air Pollution in the UK: 2003

A primary objective of the EU’s Sixth Environment Action Programme is to achieve levelsof air quality that do not give rise to unacceptable impacts or risks to human health andthe environment. The Community is acting at many levels to reduce exposure to air
pollution, through:Legislation such as the Framework and Daughter Directives
Work at the wider international level aimed at reducing cross-border pollution
Agreement with transport and industrial sectors responsible for air pollution, forexample under the Auto Oil II umbrella
Effective liaison with national, regional authorities and Non Governmental
Organisations
Research undertaken in its own or Member States’ institutes and universities.
There is no cause for complacency on the human health impacts of air pollution at a panEuropean level. In a report 4 recently published in the Lancet, experts assessed for the
first time the overall impacts of air quality and other environmental risk factors on childhealth in the WHO European Region: 14-24000 deaths every year, representing 6-10%of all mortality in children and adolescents from birth to 19 years of age, are caused byoutdoor and indoor air pollution.
The focus within the European Community for the next ten years will be implementationof air quality standards and increasing the coherency of all air legislation and related
policy effort through large-scale initiatives such as CAFE (Clean Air For Europe)5.
A Community-wide procedure for the exchange of information and data on ambient air
quality in the European Community has also been established by Council Decision
97/101/EC6. The decision introduces a scheme for the reciprocal exchange of informationand data relating to the networks and stations established in the Member States tomeasure air pollution, together with the air quality measurements from those stations.
Although progress towards Europe-wide ratification has been patchy, the 1998 Århus
convention7 on environmental openness is another important instrument; this is intended
to guarantee citizens across the continent the right to information, public participation indecision-making and access to justice in environmental matters.
We identify throughout this report a series of information resources enabling UK
technical, local authority and public end-users to obtain up-to-date information on local
or national air quality; this report, in itself, represents one of the range of published,
media and web resources intended for this purpose in the UK.

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Air Pollution in the UK: 2003

3.2 The UK Perspective
Although the lethal smogs in London and other cities caused by coal burning have now
gone for good, air pollution remains a problem in the UK. Medical evidence shows thatmany thousands of people die prematurely every year because of its effects, and this canaccelerate during extreme weather conditions. Many more become unwell or may require
hospital treatment. The young and infirm are often particularly affected, as well as
people living in deprived areas. The costs to individuals, families and the national
economy are substantial.
Air quality is therefore now one of the UK Government's key headline indicators ofsustainable development8. These provide a 'quality of life barometer' measuring everyday
concerns, and are intended to give a broad overview of whether we are achieving abetter quality of life for everyone, now and for generations to come. We’ll be looking
more closely at the latest air quality indicator levels in Section 7 of this Report.
The Air Quality Strategy for England, Scotland, Wales and Northern Ireland, firstpublished in March 1997 and revised in January 2000, has established a strong
framework for tackling air pollution over the coming years. The overall objectives of theStrategy are to:
Map out future ambient air quality policy in the United Kingdom in the medium
term
Provide best practicable protection to human health by setting health-based
objectives for air pollutantsContribute to the protection of the natural environment through objectives for theprotection of vegetation and ecosystems
Describe current and future levels of air pollution
Provide a framework to help identify what we all can do to improve air quality.
The Strategy established objectives for eight key air pollutants, based on the best
available medical and scientific understanding of their effects on health, as well as taking
into account relevant developments in Europe and the World Health Organisation. As ourknowledge of these effects has deepened, the objectives have been progressively refinedand strengthened. Moreover, objectives for a ninth pollutant, Polycyclic Aromatic
Hydrocarbons (PAHs)9 were introduced in 2003.
A summary of the current UK Air Quality Objectives in Regulation is provided in Table 1.
Corresponding objectives not to be included in Regulation for the purposes of Local Air
Quality Management (LAQM) are summarised in Tables 2a and 2b. Details ofcorresponding EC Limit Values and WHO Guidelines are provided for each pollutant in
Sections 8 to 15 of this report.
Although comprehensive and soundly science-based, these objectives are not particularly
easy for the general public to understand. A simpler air quality banding system istherefore used for media-based reporting of air quality and potential health effects to the
public (Box 1).
The UK Air Quality Strategy’s main focus is on protecting the health of the population atlarge; however, the Strategy has also established corresponding targets for theprotection of vegetation, ecosystems and the natural environment. Air monitoring
provides a key tool in assessing how far the health objectives and other environmental
targets are being met throughout the UK.

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Air Pollution in the UK: 2003

Box 1. The UK Air Quality Banding System
When air pollution is LOW (1-3) effects are unlikely to be noticed even by those
who are sensitive to air pollution.
When air pollution is MODERATE (4-6) sensitive people may notice mild effects
but these are unlikely to need action.
When air pollution is HIGH (7-9) sensitive people may notice significant effects
and may need to take action.
When air pollution is VERY HIGH (10) effects on sensitive people, described for
HIGH pollution, may worsen.

Table 1. UK Air Quality Objectives set in Regulation, 2003
Pollutant

Air Quality Objective
Concentration
Measured as

Date to beachieved by

16.25 µg m-3

BenzeneAll authorities
England and Wales only
Scotland and Northern Ireland
1,3-Butadiene
Carbon monoxide

Running annual mean

31.12.2003-3

Annual mean

31.12.2010-3

Running annual mean

31.12.2010-3

Running annual mean

31.12.2003-3

10.0 mg m

Maximum daily running
8-hour mean

31.12.2003

10.0 mg m-3

5.00 µg m
3.25 µg m
2.25 µg m

England, Wales & N. Ireland
Scotland only
Lead
Nitrogen dioxide

Particles (PM10)(gravimetric)
All authorities
Scotland only

Sulphur dioxide

Running 8-hour mean

31.12.2003-3

0.5 µg m

Annual mean

31.12.2004

0.25 µg m-3

Annual mean

31.12.2008-3

1 hour mean

31.12.2005

40 µg m-3

Annual mean

31.12.2005

50 µg m-3, not to be
exceeded more than 35
times a year

24 hour mean

31.12.2004

Annual mean

31.12.2004

50 µg m-3, not to be
exceeded more than 7 times
a year

24 hour mean

31.12.2010

18 µg m-3

Annual mean

31.12.2010

350 µg m-3, not to be
exceeded more than 24
times a year

1 hour mean

31.12.2004

125 µg m-3, not to be
exceeded more than 3 times
a year

24 hour mean

31.12.2004

266 µg m-3, not to be
exceeded more than 35
times a year

15 minute mean

31.12.2005

200 µg m not to be
exceeded more than 18
times a year

40 µg m-3

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Air Pollution in the UK: 2003

Table 2a UK air quality objectives not set in regulation, 2003
Pollutant

Air Quality Objective
Concentration
Measured as

Date to beachieved by

Ozone (for protection ofhuman health)

100 µg m-3 not to be
exceeded more than 10times a year

Daily maximum of
running 8-hr mean

31.12.2005

Nitrogen dioxide (forprotection of vegetation &ecosystems)

30 µg m-3

Annual mean

31.12.2000

Sulphur dioxide (forprotection of vegetation &ecosystems)

20 µg m-3

Annual mean

31.12.2000

20 µg m-3

Winter average(Oct-Mar)31.12.2000

Table 2b UK air quality objectives for particles not set in regulation, 2003
RegionGreater London

Greater London

Greater London

Rest of England, Wales andNorthern Ireland
Rest of England, Wales andNorthern Ireland

Objective

Measured as

50 µg/m3 not to be
exceeded more than 10times per year

24-hour Mean

23 µg/m3

Annual Mean

20 µg/m3

Annual Mean

50 µg/m3 not to be
exceeded more than 7times per year

24-hour Mean

20 µg/m3

Annual Mean

Date to beachieved by
31.12.2010

31.12.2010

31.12.2015

31.12.2010

31.12.2010

3.3 A Local Focus
Central Government and the Devolved Administrations in Scotland, Wales and Northern
Ireland are responsible for overall policy and legislation affecting the UK environment,
including air quality. However, over the last five years, the Air Quality Strategy has
enabled and encouraged Local Government to take an increasingly important role in air
quality management. Authorities are required regularly to Review and Assess air quality
in their area and take decisive action when the objectives in regulation cannot be met by
the specified target dates.
When this happens, an Authority must declare an ‘Air Quality Management Area’ andintroduce an Action Plan - which may include such measures as congestion charging,traffic management, planning and financial incentives - to tackle problems in the affectedareas.
The vast majority of local authorities in England, Scotland and Wales have now
completed their first round of reviews and assessments against the Strategy’s objectives
prescribed in the 2000 Air Quality Regulations, together with subsequent amendments10,
11.
To date 127 local authorities - over a quarter of those in UK - have established one ormore AQMAs, most of these in urban areas and resulting from traffic emissions of
nitrogen dioxide (NO2) or PM10 particles. These local authorities are now undertaking
further detailed assessments of the areas concerned and are required to submit a report

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Air Pollution in the UK: 2003

within 12 months following designation of the AQMA. The authorities have been advised
to prepare their action plans within 12-18 months of designation.
The situation is somewhat different in Northern Ireland. Here the national strategy’s
Objectives are being implemented through the Environment (NI) Order 2002 and the Air
Quality (NI) Regulations 200312,13. Currently all district councils in Northern Ireland arecompleting their first round review and assessment. Early indications are that a numberof AQMAs will be declared for roads (NO2) and area sources such as domestic heating(PM10). Northern Ireland will synchronise with the UK review and assessment timetablein April 2006, when all authorities are required to submit updating and screening
assessments.
Through the UK-wide process of Local Air Quality Management, tackling air pollution isprogressively focussing more on local ‘grass-roots’ concerns, initiatives and actions.

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Air Pollution in the UK: 2003

4. Where and how air pollution ismeasured in the UK
To manage something effectively, you first have to be able to measure it.

4.1 The Role of Ambient Air Quality Monitoring
Air quality monitoring is a key component of any effective approach to Air Quality
Management (AQM). In order to develop or implement an effective air quality
management plan at local, city or national level, it is first necessary to obtain reliable
information on ambient pollution levels. This point was fully recognised in Agenda 2114 of
the United Nations Conference on Environment and Development (UNCED), held in Riode Janeiro in 1992 and during the more recent global Johannesburg Summit15 held in
2002.
The ultimate purpose of air quality monitoring is not merely to collect data (a common
perception) but to provide the necessary information required by scientists, policy
makers and planners to enable them to make informed decisions on managing andimproving our environment.
Air monitoring fulfils a central role in this process, providing the necessary soundscientific basis for policy and strategy development, objective setting, compliancemeasurement against targets, and enforcement action. Viewed in this context,
monitoring serves the following essential key functions:Comparison of existing air quality against local, national or international standards
Assessment of population health and ecosystem impacts
Initial assessment of problem areas and pollutants requiring regulatory/control
actionProvision of baseline data for predictive models and environmental impact
assessments
Validation of emission inventory and model predictions
Determination of long-term trends
Assessment of the effectiveness - or otherwise - of control strategies over time.
In the UK, air pollution policy development relies heavily on the national air quality
monitoring networks to provide basic data on ambient concentrations. These data areused to establish priorities for policy development and to assess the effectiveness ofcontrol or regulatory action in reducing air pollution concentrations over time. Monitoringdata have also played a central role in the development of the UK’s Air Quality Strategy
and in formulating national Air Quality Objectives. In addition, measurements from our
networks provide the necessary data for determining compliance with EU Air Quality
Directives.

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Air Pollution in the UK: 2003

4.2 A Brief History of Monitoring in the UK
The history of air pollution monitoring in the UK goes back a long way. Primarily inresponse to the serious urban smogs of the 1950s and 60s, black smoke and sulphur
dioxide have been monitored on a national scale in the UK since 1961. Initially called the
National Survey, this major network - still operational today - has monitored the massive
improvement of air quality since a succession of Clean Air Acts16 successfully targeted
domestic and industrial coal burning. The emissions responsible for this type of wintersmog have decreased substantially and, as a result, road transport has now become themost important source of air pollution in many parts of the UK. In response to thishistoric change, the emphasis in monitoring has moved progressively to pollutants suchas ozone, nitrogen dioxide and fine particulate matter.
Research measurements of air pollution using automatic analysers commenced in the UK
during the early 1970s. Later, continuous measurements were increasingly required forregulatory purposes and a UK urban monitoring network was first established in 1987 tomonitor compliance with the emerging EC Directive limit values on air quality. This
network subsequently expanded, following commitments by Government to expand
urban monitoring in the UK and improve public availability of air quality information.
Another landmark year in the evolution of automatic monitoring in the UK was 1993,
when the DoE-funded Enhanced Urban Network (EUN) was established. In 1997, thisnetwork expanded following an initiative designed to promote the integration of local
authority sites into the national network where 1) this met national monitoring objectives
and 2) when appropriate quality and consistency standards could be maintained. At thesame time, increased private sector involvement in the management and quality
assurance of the networks was actively promoted. The net effect of these measures was
to increase the number and diversity of stakeholders and participants in the national
monitoring effort.
In 1995, all statutory and other urban monitoring was consolidated into one programme.
Throughout the next five years, over 50 local authority sites were integrated into theresulting network, including 14 of the London Air Quality Monitoring Network sites. In
1998, the previously separate UK urban and rural automatic networks were combined toform the current Automatic Urban and Rural Network (AURN). This presently (2003)
consists of 120 sites and remains the most important single monitoring programme in
the UK today.
The bulk of the data presented in this report originate from this network, which presently
includes 82 urban, 22 rural and 16 London Network sites: 58 sites are directly funded by
Defra and the Devolved Administrations, whilst 62 are affiliated sites owned and operated
by Local Authorities and other organisations. Future expansion of the network is alreadywell underway in 2004, with the addition of ozone and NOx analysers in rural andsuburban areas to meet the requirements of the third EC Daughter Directive17.
The dramatic continuing expansion in automatic monitoring is clearly illustrated in
Figures 1 and 2, where we show the increase in site numbers and total measurements
made since the commencement of automatic air quality monitoring in the UK.

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Air Pollution in the UK: 2003

Figure 1. The number of automatic measurement stations in the UK has grown
rapidly from 1972 to 2004

Figure 2. The number of measurements made every year has also increased
dramatically for all pollutants in the inorganic monitoring networks (O3, NO2,
CO, SO2 and PM10)

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Air Pollution in the UK: 2003

However, it’s not just the UK’s automatic monitoring networks that have expanded
massively. In fact, all of the UK’s monitoring programmes have evolved considerably
over the past 10 years. This expansion has been driven by many factors, including
increasing concern about health impacts, government’s desire to inform the public of thequality of our air, the UK’s air quality strategy and a range of European commitments.
There has also been considerable growth in the amount of monitoring undertaken by
Local Authorities. Many of these sites now contribute data to nationally organised
measurement programmes funded and supported by Central Government and the
Devolved Administrations.
It should be emphasised that this report deals only with measured data from national
monitoring programmes, including local authority sites that are affiliated to these
programmes. All sites in these networks are subject to stringent quality control
programmes that ensure measurement consistency and accuracy (see Sections 4.3 and
4.4). The value of air quality monitoring undertaken by Local Authorities should not be
underestimated, however. Information from these monitoring sites provides a soundbasis for Local Air Quality Management, planning and decision-making. The quality ofdata from these programmes is also high. Many sites not affiliated to national networks
are now subject to the same level of quality assurance and control procedures as used inthese programmes; this ensures that measurement quality and integrity is fully
harmonised with national networks.

4.3 The current situation
There are currently over 1300 national air quality monitoring sites across the UK,
organised into several automatic and non-automatic networks with different scope andcoverage. Clearly defined objectives have been set for each of these, in order to optimise
network design, select priority pollutants and appropriate measurement methods, anddetermine the required level of quality assurance/control and data management. As
noted in the introduction, the primary objectives of current UK networks are:To understand air quality problems in order that cost-effective policies and solutions
can be developed
To assess how far UK and European standards and targets are being achieved
To provide public information on current and forecast air quality
To assist the assessment of personal exposure to air pollutants.
However, in practice, each network offers a different balance of objectives, and is
structured, organised and quality controlled accordingly.
125 of these sites in the AURN (120) and hydrocarbon networks (5) operate
automatically; these provide high-resolution hourly information on a range of pollutants
that is communicated rapidly to the public. The non-automatic sites measure average
concentrations over a specified sampling period (typically from a day to a month) insteadof instantaneous concentrations, but still provide invaluable data for assessing levels andimpacts of pollution across the country as a whole.
A map of current UK automatic monitoring sites is provided in Figure 3. In theaccompanying Figures 4.1-4.3, we map corresponding sampler-based measurement sites
and show how the different networks provide comprehensive measurement coverageover the UK. Maps showing measurement coverage in different parts of the UK arepresented in Appendix 2, whilst additional site maps for individual pollutants feature in
Sections 8-15 of this report.
The UK’s combined use of both automatic and sampler-based programmes for air
monitoring has evolved over the last 40 years as the best way of quantifying pollutant
behaviour in both space and time, whilst also maximising cost-effectiveness. Thisapproach uses sampler measurements to provide good spatial coverage, area-resolution
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Air Pollution in the UK: 2003and ‘hot-spot’ identification. Samplers can also be used to provide compliance data forpollutants such as benzene, where European Limit Values apply for annual average
concentrations. By contrast, automatic analysers, deployed at carefully selected
locations, provide more detailed time-resolved data for assessing peak concentrations
and for comparison with short-term UK Air Quality Objectives or European Limit Values.
The pollutants measured, site numbers and areas covered in the UK’s nationally coordinated monitoring networks are summarised in Table 3 below, whilst the mainfeatures of individual programmes are summarised in Table 4. Further information on the
different UK air monitoring networks is provided in Appendix 3.
Table 3. Summary of UK measurements made for the most important air
pollutants
Pollutant

Major sources

Site numbers

Areas covered

Nitrogen Dioxide(NO2)
Ozone (O3)Road transport andindustry
Sunlight and heat,
acting on road transport
and industrial emissions
Road transport,
industry, construction,soil and natural sources
Industry and fuelcombustion

106 (Automatic)
1288 (Non-automatic)
85 (A)

Mostly urban

Particles (PM10 andPM2.5)
Sulphur Dioxide
Carbon Monoxide(C0)Volatile Organic
Compound (VOCs)
Dioxins and PCBs
Polycyclic Aromatic
Hydrocarbons(PAHs)
Metals- Pb, Cd, As,
Ni and Hg
Acid Deposition

Ammonia
Nitric Acid

Road transport

68 (A)
7 (NA) gravimetric
123 (NA) black smoke
76 (A)
123 (NA) net acidity
32 (NA)
79 (A)All of UK- urban
and rural areas
Mostly urban
Mostly urban
Rural
Urban

Industry, transport,
solvent use and somenatural sources
Combustion (dioxins)
and past uses (PCBs)
Industry and traffic(PAHs)5 (A)
35 (NA) benzene
9 (NA) 1,3-butadiene
6 (NA)

Mostly urban

24 (NA)

Industrial, urban
and rural

Industrial and otherprocesses
Atmospheric reactions
involving fuel burning,
agricultural and otheremissions
Agricultural activities
Combustion andphotochemistry

17 (NA)
38 (NA)

Industrial, urban
and rural
Rural

93 (NA)
13 (NA)

Rural
Rural

3 urban 3 rural

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Air Pollution in the UK: 2003

Figure 3. Current UK Automatic Air Quality Monitoring Stations

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Air Pollution in the UK: 2003

Fig 4.1 Current UK sampler-based measurement programmes in urban areas

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Air Pollution in the UK: 2003

Fig 4.2 Current UK sampler-based measurement programmes for Persistent
Organic Pollutants (POPs) and metals

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Air Pollution in the UK: 2003

Fig 4.3 Current UK sampler-based measurement programmes: Acidification andEutrophication

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Air Pollution in the UK: 2003

Table 4. The major UK Air Quality Monitoring Networks
Network
The Automatic Urban and Rural
Network (AURN)
The non automatic network forsmoke, SO2 and NO2
Rural acid deposition, gases andparticles
Automatic Hydrocarbon
Toxic
Organic
Micropollutants(TOMPS)
Polycyclic Aromatic Hydrocarbons(PAHs)
Lead and Multi-element
Rural metal deposition network

Auto orSampler?
A

No of Sites

SAS

131 (Smoke and SO2)
1288 (NO2)
38 (acid deposition)
32 (SO2 )
5
6

S

18

S
S

17
10 particle and rain
3 rainwater
2 cloud water all rural
35 (benzene)
9 (1, 3-butadiene)
93
13

S

Benzene and 1,3-butadieneS

Ammonia Network
Nitric Acid

SS

120 (82 urban, 22 rural, 16 London)

Many of the networks, and particularly those involving automatic measurements, arelarge-scale and involve a wide range of participating organisations. A good example is
the AURN; this has a devolved structure with separate specialised organisations
performing different duties (Figure 5). There is also an important role for localorganisations, which are typically responsible for ongoing site operations. However,overall management and quality assurance functions for the network are centrally coordinated in order to ensure fully harmonised and consistent outputs. The data from thisand similar networks, presented in this report, therefore represent the end-product of theefforts of many persons and organisations in the private sector, local and central
government.
Figure 5. A devolved network organisational structure, as employed within thelarge-scale AURN programme.

UK
GovernmentDefra

The European
Commission

CentralManagement
Unit CMCU

Independent
QA/QC Unit

Local Site
operators
LSOs

Equipment
Support Unit
ESU
Public Air
Quality
Information
Service

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Air Pollution in the UK: 2003

Two defining characteristics of the UK national air monitoring effort may be seen as:1) Its focus on quality assurance and control (QA/QC) to maximise measurement
integrity and reliability2) An emphasis on achieving the widest possible dissemination and use of bothmonitoring data and the information derived from this.
In subsequent sections, we will examine both the UK’s QA/QC programmes and air
quality information services in more detail.

4.4 Emphasis on Data Quality
The UK air monitoring networks produce over 12 million individual measurements every
year. In order for these data to be useful and provide a sound scientific basis forcomparison against standards, public information or policy development, we need to be
sure that they are accurate and reliable. This is why considerable attention is devoted in
the UK monitoring networks to quality assurance and control.
Quality Assurance and Control
A system of activities that assures that measurements meet defined standardsof quality with a stated level of confidence
Each UK network therefore has in place a strong QA/QC programme designed to ensurethat its measurements meet defined standards of quality with a stated level of confidence.
Essentially, each programme serves to ensure that the data obtained are:(i)

Genuinely representative of ambient concentrations existing in the various
areas under investigation(ii)

Sufficiently accurate and precise to meet specified monitoring objectives(iii)

Comparable and reproducible. Results must be internally consistent andcomparable with international or other accepted standards, if these exist(iv) Consistent with time. This is particularly important if long-term trend analysisof the data is to be undertaken(v)

Representative over the period of measurement; for most purposes, a yearlydata capture rate of not less than 90% is usually required for determining
compliance with EC Limit Values(vi) Consistent with the Data Quality Objectives defined in EC Daughter Directives.
The UK’s Quality Assurance and Control programmes typically include a broad spectrum ofsystem design, operational management, training and review activities.
For the AURN, these activities are tasked to an independent QA/QC Unit (Figure 5), which
carries out the following functions:
Quality assurance (of measurement processes):-

Advice on network design, site selection and siting
Support in instrument selection and sample system design
Development of operations manual and monitoring compliance
Operator and personnel training

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Air Pollution in the UK: 2003

Quality control (of outputs):-

Monitoring routine site visits and operations
Monitoring calibration gases and instrument response
Routine data inspection review and validation
Data ratification/finalisation before archival

Quality Assessment-

Regular network audits and site inspections

Through these activities, we ensure that the data produced by this network and reported
here are fit-for-purpose, reliable and accurate.

4.5 Disseminating and using air quality data - andwhere to find out more
As discussed previously, the UK’s air monitoring programmes produce very large
amounts of data. However, in isolation, these raw data are of very limited utility. We firstneed to ensure that the data are accurate and reliable; this is a major quality control
task, as highlighted in the previous section. Once this has been done, the validated data
are archived, transformed into useful information and communicated to government,
technical, local authority and public users in timescales and formats meeting their needs.
This process of turning raw data into useful information, depicted in Figure 6, is vital to
the success of the UK monitoring networks. The UK’s Air Quality Archive and Air
Quality Information Service are our key tools enabling the widest access and use of
air quality information in the UK.
As noted in the introduction to this report, a primary objective of Government’s air
quality monitoring networks is to provide rapid and reliable air quality information to the
public. The Air Quality Information Service provides the main link between the networks
and the public at large. Data from all the UK’s automatic monitoring stations areautomatically collected every hour and uploaded to the UK’s Air Quality Archive.
Corresponding data from sampler measurements programmes are also collected andmerged with the archive. The resulting archive contains over 150 million measurement
and statistical records, making it one of the largest publicly accessible online databasesin the world.
Data collected from the automatic networks are also rapidly collated, checked andcompared with UK and European air quality targets and objectives. Exceedences of highor very high air quality bands (see Box 1) initiate a range of co-ordinated actions by
Government and the media to further inform and advise the public. Air quality data fromthe UK automatic networks, together with twice-daily pollution forecasts, are widely
disseminated by a range of electronic and web-based media; these include a freetelephone service, and TV Teletext, as well as globally via the World Wide Web (Figure 7
and Box 2). Information on UK air quality is also frequently exchanged with othercountries in Europe, to enable us to track pollution being transported over long distances.
The UK’s Air Quality Archive is the national repository for ambient air quality
measurement and emissions data. It contains measurements from national automatic
measurement programmes dating back to 1972, together with sampler measurements
dating back to the early 1960s. The Archive brings together into one coherent databaseboth data and information from all the UK’s measurement networks, as well as
corresponding detailed emission data from the National Atmospheric Emissions Inventory(NAEI).

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Air Pollution in the UK: 2003

Measure andcollect raw
data
Quality control, checkand validate
Compile reliable
Air Quality
database
Analyse, map,
interpret

Produce useful
information
Report, disseminate byweb, media etc.
Use theinformation
effectively

Figure 6. This report has been made possible by turning large
quantities of raw air quality data into useful information
All data and information stored in the UK’s Air Quality Archive are freely available atwww.airquality.co.uk The website provides user-friendly but comprehensive access to
information on all air pollutant concentrations and emissions, together with up-to-datebulletins and measurements from the UK national monitoring networks. It also provides
a twice-daily air quality forecast, which is further disseminated via TV Teletext,
newspapers and a free telephone service. Finally, the website offers many pages ofbackground information and advice on air quality, together with links to other UK andinternational information resources. See box 3 for further details of information available
from the website and Figure 8 for a map of the site.
The UK’s national air quality web site currently records over 4,000 hits each day and is a
key resource for UK education and research. It has received wide praise, both within the
UK and internationally.

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Air Pollution in the UK: 2003

Figure 7. The UK Air Quality Information Service
This utilises a wide variety of media, web and electronic resources to disseminate
the latest air quality data and forecasts:

TV Weather Bulletins

TV Teletext

The UK Air Quality Website

Twice daily web forecasts

A series of brochures & reports

Freephone 0800 556677

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Air Pollution in the UK: 2003

Box 2. Key Online and Media Information Resources on UK Air
Pollution
1) How to obtain up-to date air quality information and forecasts for your
area

•
•
•
•
•

•
•
•
•

The Air Pollution Information Service on freephone 0800 556677
The UK Air Quality Archive on www.airquality.co.uk
Latest forecasts, issued twice daily, at
http://www.airquality.co.uk/archive/uk_forecasting/apfuk_home.php
The National Atmospheric Emissions Inventory on www.naei.org.uk
The Defra air quality information web resource on
http://www.defra.gov.uk/environment/airquality/index.htm
The Scottish Executive Air Quality pages on
http://www.scotland.gov.uk/about/ERADEN/ACEUAQT/00016215/homepage.aspx
The Welsh Assembly Government Environment link at
http://www.wales.gov.uk/subienvironment/index.htm
The Northern Ireland Environment and Heritage Service website at
http://www.ehsni.gov.uk/environment/environment.shtml
Teletext page 156

2) Useful Sources of Background Information
A colourful brochure ‘Air Pollution in the UK’, suitable for educational or public use, isavailable from Defra Publications at: defra@iforcegroup.com or 08459 556000
A comprehensive range of air quality research reports is available fromhttp://www.airquality.co.uk/archive/reports/list.php
3) Health Effects of Air Pollution
A concise brochure entitled ‘Air Pollution, what it means for your health’ isavailable to download from the Defra air quality information web resource listed aboveor free of charge from Defra publications or via Freephone.
4) Local Air Quality Issues
For further information on air quality issues in your area, please contact theEnvironmental Health Department at your local Council office.
Further information on Local Air Quality Management may also be found at:
http://www.defra.gov.uk/environment/airquality/laqm.htm andhttp://www.airquality.co.uk/archive/laqm/laqm.php

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Air Pollution in the UK: 2003

Box 3. Information Available from the UK Air Quality Archive at
www.airquality.co.uk•

Historic measurements from all national sampler and automatic air monitoring
programmes•

Current measurements from automatic networks, speedily available for all UK
regions and urban areas•

Detailed air pollution statistics derived from all current and historic data andavailable via interactive selections•

Twice-daily regional forecasts of air quality•

Maps, photographs and descriptions of all automatic network stations•

Information on causes and effects of the major air pollutants•

Details of UK and international efforts taken to tackle air pollution•

A database of Frequently Asked Questions (FAQs) and answers related to air
pollution•

Search-driven information and access to reports covering a wide range of Air
Pollution issues•

Background information on a range of Local Air Quality Management (LAQM)
issues including:
Air Quality Management Areas
LAQM tools
Helplines
Reports and FAQs•

Links to the National Atmospheric Emissions Inventory (NAEI) site which offers:
Information on how the inventory has been prepared
A data warehouse of emission factors and inventory tools
UK–wide maps of emissions of the major pollutants (1km resolution)
Mapped emissions for different source types - industrial, transport etc
A powerful search facility for finding local emissions by postcode input
Information on a broad range of climate change issues•

A range of useful links to air pollution data resources, organisations andinformation in the UK, Europe and worldwide

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Air Pollution in the UK: 2003

Figure 8 Map of the UK Air Quality Archive, showing the comprehensive
range of available data and information from this resource

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Air Pollution in the UK: 2003

5. High Pollution Episodes
We focus on periods when pollution levels are unusually high, either
locally or UK-wide. Through examining some recent episodes, we
identify causes and examine their possible impacts.
Air pollution levels can vary considerably from day to day, as well as from one part of thecountry to another. In this section, we’ll look at short-term variations over time, and inparticular some recent periods when pollution levels were particularly high. These areusually referred to as episodes. In the next section, we focus more on variations inpollution levels from area to area.
Pollution levels vary over time for two main reasons:
1) Variations in pollutant emissions
2) Changes in atmospheric conditions that allow pollution levels to build up or resultin the transport of pollutants from other areas.
All episodes occur because of a combination of these factors.
There are two main types of pollution episode in the UK- winter and summer smogs.
Winter smogs typically occur in cold, still and foggy weather; this traps pollution
produced by motor vehicles, space heating and other sources close to the ground andallows it to build up over time. City areas - in particular those close to major roads - areusually worst affected, together with sheltered or low-lying parts of the country. Winterepisodes are characterised by elevated levels of nitrogen dioxide (NO2), particles (PM10)
and volatile organic compounds (VOCs) such as benzene. High sulphur dioxide levels canalso occur in some industrial or coal-burning regions.
Bonfire night can sometimes provide an interesting example of an emissions-driven
winter episode. Given cold, stable weather – poor conditions for dispersing emissions widespread bonfires can result in elevated levels of PM10 particles in many urban areas of
the UK.
By contrast, summer smogs occur in hot, still and sunny weather. Sunlight and hightemperatures accelerate chemical reactions in mixtures of air pollutants that are emitted
from road vehicles, fuel burning and solvent usage. The pollutants that cause such an
episode can often travel long distances - sometimes from other parts of Europe. During
this large-scale air movement, they react together to produce high levels of ozone (O3),
together with other pollutants such as nitrogen dioxide and particles. Unlike the ozone
layer in the upper levels of the atmosphere that protects us from ultraviolet radiation,
ground level ozone produced in this way is harmful to human health and vegetation, as
well as damaging some man-made materials.
Long-range transport of pollutants from Europe, or occasionally from North Africa orNorth America, can on occasions cause another type of pollution episode. This tends tooccur during the summer months, either in isolation or in combination with summer
smog. Local transport episodes involving elevated levels of primary (directly emitted)
pollutants may also occur in the proximity of large industrial plant.
Air pollution episodes in the UK vary widely in terms of the size and location of the areas
they affect, duration and seriousness. Here we examine five episodes, one of eachspecific type described above.

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Air Pollution in the UK: 2003

5.1 A winter smog episode: December 2001
Historically, the first half of December is particularly associated with winter smogs in theUK; in fact, many of the most notorious coal-burning smogs occurred at this time ofyear. The historic London smog of 1952, which first galvanised Government and public
action to tackle air pollution, occurred in the first week of December. As discussed in
Section 7, where we examine long-term pollution trends, these smogs no longer occur inmost of the UK. However similar episodes, albeit of reduced severity, can still occur inareas such as Northern Ireland, where coal is still widely burnt for domestic spaceheating.
The cold, stable weather that initiates winter smogs also allows pollutants from motor
vehicles and other sources to accumulate over time. As a result, winter smogs can now
be associated with elevated levels of a wide range of pollutants. A good example ofwinter smog associated with road transport emissions occurred between the 7th and 18th
December 2001. The main pollutants involved were PM10 particles and nitrogen dioxide,
although sulphur dioxide levels were elevated throughout the period in Belfast.
High atmospheric pressure dominated the UK weather patterns during this pollution
event. This is a characteristic weather pattern for winter smogs; it is usually associatedwith low wind speeds, cold, misty or foggy conditions and well-defined atmospherictemperature inversion layers which act as a barrier to the dispersion of pollutants,
trapping them close to the ground. As a result, pollutant concentrations during wintersmogs tend to build up slowly over time - the longer the stable conditions last, the higher
the levels of pollution reached. In Figure 9 overleaf, we graph the number of monitoringsites exceeding the moderate, high and very high air quality bands for PM10 during theepisode; this clearly shows the build-up and decline in overall pollutant levels over time.
During the episode’s peak from the 11th onwards, the high-pressure system was centred
over Northern Britain and Ireland (Figure 10), resulting in elevated concentrations of arange of pollutants over this part of the country, Central Scotland and Northern Ireland.
Overnight levels of PM10 reached the VERY HIGH band in Glasgow (104 and 119 µgm-3)
and HIGH in Edinburgh, Manchester and Belfast. These levels were primarily attributable
to road transport emissions, although local sources (nearby construction and a Christmas
Fayre) also influenced peak PM10 levels in Edinburgh. Domestic heating was an importantfactor at Belfast, resulting not just in elevated PM10 but also sulphur dioxide
concentrations in the city. From the 14th onward, wind directions shifted to northerly andspeeds increased. The resulting improvement in atmospheric dispersion brought theepisode to an end.

5.2 A Bonfire Night Episode: 5 November 2002
Although bonfires and firework displays occur in many parts of the UK every November
5th, as well as during adjacent weekends, meteorological conditions strongly affect theresulting pollutant concentrations. Wet, windy or unsettled conditions result in low
concentrations; cold and still weather may result in elevated levels of PM10 particles andother pollutants.
Generally, PM10 levels in 2002 were lower than in previous years, with elevated measured
concentrations being confined to a few small areas, often at sites having comparatively
high background levels. The uncharacteristically low pollutant concentrations were
attributable to unsettled weather, with moderate to strong westerly winds bringing clean
Atlantic air masses and providing effective dispersion conditions over most areas of theUK. Heavy rain showers will also have helped to remove particulate matter from theatmosphere, as well as discouraging firework displays and bonfire night celebrations. In
some parts of England, however, winds dropped and more stable conditions prevailed
during the 4th and 5th. This resulted in PM10 concentrations rising to the moderate band atseveral measurement sites, mostly in London.
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Air Pollution in the UK: 2003

20
18
Moderate

16
14

No of UKsites in
band

High

12
10

V.High

8
6
4
2

-D
ec
18

-D
ec
16

-D
ec
14

-D
ec
12

-D
ec
10

-D
ec
08

06

Date

-D
ec

0

Figure 9. Pollution levels build up slowly during winter smogs

Figure 10. High-pressure systems like this on 12th December are closely
associated with winter smog episodes in the UK (Crown Copyright)

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Air Pollution in the UK: 2003

Figure 11 shows very clearly how Bonfire Night particle concentrations can vary markedly
from year to year. It confirms 2002 to have been a relatively quiet year, with 1994 and1995 being the most recent years characterised by UK-wide exceedences of the current
24-hour running average PM10 objective of 50 µg/m3.

Figure 11. Bonfire night PM levels (running 24-hour average over all UK sites)
compared to objective of 50 µg/m3 for all years from 1994 to 2002

5.3 A Summer Smog Episode: August 2003
2003 proved to be a record-breaking year for the UK and global climate. It was thesunniest on record for England and Scotland, the warmest ever in Scotland, and thesecond driest year in England and Wales since 1766. The highest ever UK temperature of
38.5oC was recorded in Faversham, Kent on 10th August. Taken overall, 2003 was thefifth warmest for Britain as a whole since records began in 1659.
The extreme conditions were not just confined to the UK. 2003 was the third warmest
year worldwide since global records began in 1861, and the hottest ever over many partsof Europe (Figure 12). It is interesting to note that all of the planet’s ten hottest years
have occurred since 1990, providing solid evidence of a worldwide climate trend.
These extreme weather conditions caused photochemical ozone production over large
areas of UK and Europe. 2003 was notable both for very early (April) and late
(September) summer smogs in the UK. The most exceptional of these was the episodethat occurred during the very hottest part of the year, the first half of August (Figure13). During the period from 1st to 15th August, many rural and urban monitoring stations
across England and Wales recorded hourly ozone levels in the HIGH (180-360 µgm-3)
band; the highest single hourly measurement was 250 µgm-3 at Lullington Heath (East
Sussex) on the 11th. Moreover, high concentrations were recorded for 10 consecutive
days, an unusually long period for an ozone episode. During much of this period, airtransported from continental Europe strongly influenced pollution levels over much of the
UK (Figure 14).
However, despite record-breaking temperatures, cloudless skies, sunshine and apersistent, stable high pressure system - all conditions closely associated withphotochemical episodes - corresponding pollution levels in August did not break UK
records. In fact, comparisons with the similar ‘heat wave’ summer of 1976 showed thatmaximum hourly ozone concentrations in 2003 were approximately 50-60% of thoserecorded during that year. This is consistent with the marked UK and Europe-wide
decline in emissions of ‘precursor’ pollutants (nitrogen oxides and volatile organic
compounds) in the years between 1976 and 2003.
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Air Pollution in the UK: 2003

During the August heat wave, severe temperatures and elevated ozone levels wererecorded in many parts of Europe, together with large numbers of reported deaths. It is
often difficult to distinguish deaths caused by heat stroke, dehydration and exhaustion
from those due to air pollution. Very often, multiple factors are involved. The UK Officefor National Statistics has reported an additional 2045 deaths in England and Wales forperiod from 4th to 13th August 2003, when compared against the 1998-2002 average
mortality figures for that time of year. Using previously well-established medical data on
the effects of ozone and PM10 on human health, it has been estimated that between 423
and 769 of the additional deaths were associated with elevated concentrations of thesepollutants. This represents between 21% and 38% of the total excess deaths recorded
during this period.

5.4 An Episode involving Long-range Transport:
March/April 2003
This period was interesting for a number of reasons. From mid-March to the end of themonth, elevated PM10 particle levels in the MODERATE (24 hour running average
exceeding 50µgm-3) or HIGH bands (over 75 µgm-3) were observed at an increasing
number of sites. A VERY HIGH measurement of 104 µgm-3 was recorded in Sheffield on
the 24th March. This may well have been due to nearby city centre or industrial sources.
For much of the period, however, meteorological analyses showed that air quality
nationwide was strongly influenced by primary pollutant emissions from Central orNorthern Europe, together with secondary particles subsequently produced by chemical
reactions in the atmosphere. When cleaner Atlantic airflows became dominant in early
April, levels of all pollutants dropped drastically.
On the 12th April, levels of both ozone and PM10 began to increase at many monitoring
stations. This rise was associated with unusually warm and sunny weather for the time ofyear, combined with air transported from Scandinavia and Central Europe. From the 14th
onwards, however, winds became stronger and more southerly and elevated PM10 levels
up to the VERY HIGH band (118 µgm-3) were recorded in Northern England. Images fromthe US SeaStar satellite, part of NASA’s Earth Science Enterprise, provide a fascinating
glimpse of global long-range transport of dust and pollution during this period (Figure15). The images show the UK almost hidden beneath tan-coloured swirls of Saharan dust
and grey haze associated with polluted continental air.
As particle levels rose, so did those of ozone, reaching the HIGH band at several
locations. As noted previously, April is unusually early for elevated levels of ozone to beobserved in the UK. Long-range transport of air dominated throughout this period,
bringing in continental ozone and its precursors, with particle levels also likely to havebeen influenced by the large-scale Saharan dust storms.

5.5 An Episode involving Short-range Transport: May
2002
Short-term elevated levels of primary pollutants can be observed in the proximity ofmajor emission sources such as power stations, refineries or large industrial plant. Suchepisodes tend to be intermittent, highly localised and associated with rapidly fluctuating
concentrations. In the case of sulphur dioxide, for instance, increasingly stringent
emission controls and the move towards lower-sulphur or clean fuels such as natural gas
mean that such events are now becoming increasingly rare. The most recent clearcut
example of such a point-source episode for SO2 was seen in May 2002 in Grangemouth,~ 1km from the nearby large refinery, where measured peak 15-minute average
concentrations up to 1346 µgm-3 were observed; by comparison, the relevant short-term
UK objective for 2005 states that a concentration of 266µgm-3 should not be exceeded
more than 35 times per year.

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Air Pollution in the UK: 2003

Figure 12 NASA analysis of MODIS
satellite data showing temperature
anomalies (above normal) acrossEurope during July 2003 (Courtesy the
Visible Earth Team)

Figure 13 London’s Canary Wharf
during the height of the August 2003
summer smog

Figure 14 Meteorological analysis
showing transport of air from Continental
Europe to different parts of the UK
during the August 2003 summer smog

Figure 15 NASA SeaStar satellite
image showing strong transport ofair and dust to UK from the south
on 15 April 2003 (Courtesy the
Visible Earth Team)

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Air Pollution in the UK: 2003

6. How air pollution varies acrossthe UK
We examine how levels of air pollution vary across the UK, and see
how these variations relate to both emissions and the behaviour ofpollutants once emitted into the atmosphere.
Levels of air pollutants vary markedly across the country. Measurements from thenational air monitoring networks clearly show that these patterns differ for eachpollutant, depending on how they are formed and where their major sources are located.
Levels of primary pollutants, those emitted directly into the atmosphere, tend to behighest around their sources; these are usually located in urban and industrial areas.
Sulphur dioxide provides a good example of such a pollutant, with domestic or industrial
fuel burning being its major sources nationwide. As illustrated in the last section, thehighest sustained levels of this pollutant are often found during winter in parts ofNorthern Ireland, where solid fuel is still used extensively for domestic heating.
Measurements from the UK monitoring networks can be combined using empirical models
with detailed pollutant emissions data from the UK’s National Atmospheric Emissions
Inventory (NAEI). Together, these provide the basis for robust, empirical pollutant
models which now enable us to produce detailed maps (1km resolution) of average or
peak pollutant concentrations across the country. The mapping method is detailed in a
number of published reports on the UK Air Quality Archive- for example, the report for
Defra and the Devolved Administrations entitled ‘Mapping of nitrogen dioxide and PM10 in
the United Kingdom for Article 5 Assessment’ and subsequently published at
http://www.aeat.co.uk/netcen/airqual/reports/aeat-env-r0707.pdf. The main benefit of
the model is that it is simple and directly related to the measurements. No complicatedmeteorological fields, emissions factors or local information is required.
These maps enable the UK to fulfil its European commitments to assess nationwide
pollution patterns prior to implementing the European Air Quality Directives. They also
provide an extremely powerful tool for identifying pollutant ‘hot-spots’ and managing UKwide air quality problems in the most direct and cost-efficient manner.
A map showing average SO2 levels across the country is shown in Figure 16. This clearlyshows the impact of power station and industrial emissions in Northern England, theThames Estuary and Forth Valley, as well as domestic emissions focussed around Belfast
in Northern Ireland.
Motor vehicles are now a major source of air pollution in many large cities. In particular,
most of the carbon monoxide, nitrogen dioxide, and volatile hydrocarbons (VOCs) suchas benzene and 1,3-butadiene are emitted from traffic, together with a significant
proportion of particles (PM10). Concentrations of all these pollutants are therefore usuallyhighest in built-up urban areas.
In general, patterns of secondary pollutants such as ground-level ozone - which areformed by chemical reaction in the atmosphere - are markedly different from those of
primary pollutants; they are characteristically less dependent on emission patterns, andtend to be more strongly influenced by meteorology and atmospheric chemistry. As aresult, they also change more from year to year than those of primary pollutants. UKwide concentrations of ozone are shown in Figures 17.

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Air Pollution in the UK: 2003

As highlighted previously, ground-level ozone is formed by a series of chemical reactions
involving precursors pollutants - oxides of nitrogen and hydrocarbons – together withoxygen. Ultraviolet radiation drives these reactions and, as a result, ozone production
rates are highest in hot, sunny weather. Ozone formation can take from hours to days tocomplete. Consequently, high levels of ozone can often be formed considerable distances
downwind of the original pollution sources in UK or Europe.
UK-wide patterns of ground-level ozone are also influenced by other factors.
Concentrations in busy urban areas are often lower than in the surrounding countryside.
This is because road transport emissions react very quickly with ozone to remove it fromthe atmosphere. Because ozone is very reactive, it is also readily deposited onto theground or adsorbed onto vegetation. These removal processes tend to be more importantin sheltered, lowland areas than exposed higher altitudes. As a result, ozone levels areusually higher on elevated ground.
The net result of all these effects, acting together, is shown in Figure 17. The highest
summer ozone concentrations (here graphed as accumulated total hours over 80µgm-3
for 2001) are seen in the rural parts of South and South East England; these areas tend
to be hotter and sunnier than other parts of the UK, and are often downwind of polluted
areas of Northern Europe. Elevated concentrations are also seen in parts ofCentral/Eastern Scotland, due to its altitude. However, the fine detail in these annualozone maps changes from year to year, and other years have shown evidence ofelevated concentrations in hilly parts of Wales. Although not mapped here, ozone levels
are characteristically depressed in urban areas, as a result of its ‘scavenging’ from theatmosphere by road transport emissions.
The vast majority of Air Quality Management Areas (AQMAs) in the UK are due to current
or predicted exceedences of air quality objectives for nitrogen dioxide (NO2) or PM10
particles. We’ll now examine UK-wide patterns of these pollutants more closely.
UK-wide patterns of nitrogen dioxide concentration are shown in Figure 18; these aremarkedly different from those of ozone or sulphur dioxide. Although some NO2 is emitted
directly from vehicles or other sources, most is formed by rapid chemical reaction in theatmosphere. This pollutant therefore has both secondary and primary characteristics.
Concentrations of nitrogen dioxide tend to be highest in urban areas such as in London,
where traffic densities are high. Although the data mapped in the figure are backgroundrather than roadside pollution levels, they clearly follow closely the country’s major
motorways and road network infrastructure.
Particles are not a distinct chemical species like the other pollutants measured in theautomatic networks; rather, they consist of material from many sources and are usuallyclassified on the basis of size and not chemical composition. In the UK automatic
networks, particles of average aerodynamic diameter less than 10 microns (where one
micron is a thousandth of a millimetre) are measured. These fine particle fractions can beinhaled deep into the lungs, and therefore provide a better indication of potential healthimpacts than larger particle size ranges.
The sources of PM10 particles are diverse. They are produced from motor vehicles, fuelburning, building work, industrial emissions, soil and road dust and quarrying. A
significant proportion of PM10 particles are secondary, formed by the reaction of gases in
the air. Particles of ammonium sulphate and ammonium nitrate are produced by thesame photochemical reactions that give rise to ozone. Like ozone, secondary particles
can therefore be formed considerable distances from the emission sources. This diversityof PM10 source types and influences is reflected in the map of average concentrations inFigure 19, which shows markedly less variation across the country than for the otherpollutants assessed here.

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Figure 16. Background SO2, annual average
concentrations in 2003 (µg/m3)

Figure 17. Accumulated ozone hours over 80µg/m3, summer 2001

Figure 18. Annual average NO2 levels in 2003(µg/m3)Figure 19. Background PM10 levels in 2002(µg/m3 gravimetric)

Figures 16-19 show mapped concentrations of four major pollutants (SO2, O3,
NO2 and PM10); these have been estimated using models based on national
monitoring and emissions inventory datasets.

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7. How air pollution has changed
over time
Is air pollution getting better or worse? Here we find out, but theanswers are not always clearcut.

As highlighted in previous sections, the concentrations of air pollutants in the atmospherecan vary over the course of a day, the seasons of a year and from year to year. In thissection, we focus on long-term trends in the UK’s air quality, and attempt to answer the
perennial question - ‘are things getting better or worse?’ As always, the answer to such a
straightforward question is not clearcut. It really depends on what pollutants we’re
examining, and over what timescales.
Very reliable indications of long-term trends can be derived from UK monitoring data. As
noted previously, large-scale national measurements of black smoke and sulphur dioxidebegan in the early 1960s. This national network, established in response to the recurring
serious smogs of that era, was probably the earliest air quality measurement programmeof this scale and sophistication in the world. At its peak, it included over 1200
measurement sites. The main objectives of this network were to assess nationwide levelsof these ingredients of coal smog, and to analyse how these have changed over time;over the 40 years of its operation, both of these network goals have been met in full.
In Figure 20, we show annual average levels of both pollutants from the establishment of
the network in the 1960s. The picture shown here is most encouraging. It demonstrates
that overall levels of sulphur dioxide have fallen nearly 10-fold, and smoke levels 20-fold.
Corresponding measurements from later automatic measurements since 1970 tell thesame story, with urban background SO2 levels now barely distinguishable from those inrural areas.
The dramatic decline in atmospheric concentrations of these pollutants mirrors closely
the fall in national emissions of both pollutants. This is because far less coal is used fordomestic and small-scale heating, smoke control measures have been universally applied
through a series of Clean Air Acts, and cleaner fuels and fuel-burning technologies havebeen widely adopted. Overall, the successful regulation and taming of coal burning andits emissions represent a remarkable success story for air quality management in the UK.
However, this did not mark the end of air pollution problems in the UK. Road transport
and industry remain major sources of pollution, with vehicle emissions being the mostimportant factor affecting air pollution in our cities. The shift from an air pollution climate
dominated by coal burning to one most influenced by road transport has occurred incountries world-wide. In many parts of China, for instance, we see pollution climates in astate of transition, with coal burning and a burgeoning vehicle fleet both adding to theurban air quality burden.
Long-term trends of a wide range of air pollutants can be tracked in Britain since theearly 1970s; this was when automatic measurements of many other species- including
secondary pollutants and those produced primarily by road transport- commenced inearnest. Even clearer trends have become apparent since the massive expansion of thescale and coverage of national measurements over recent years.
Long-term trends for individual pollutants are graphed for a range of site types- urban,
rural, near-road and others- in Part 2 of this report.

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Air Pollution in the UK: 2003

In Figure 21, we show the UK Government’s air quality headline indicator of sustainable
development since 1987; urban and rural trends are shown separately. This figure shows
the average number of days on which levels of any one of a basket of five pollutants(carbon monoxide, nitrogen dioxide, ozone, fine particles and sulphur dioxide) were'moderate or higher' according to the Air Pollution Information Service bandings listed
earlier in Section 2 of this brochure. These five pollutants are recognised as the mostimportant for causing short-term health effects.
To supplement this information, we show separately in Figure 22 the average number ofdays of pollution at urban sites since 1993 caused by each individual pollutant.
There is a wealth of information contained in these figures, from which we can extract a
number of key conclusions. Firstly, it’s clear that 2003 was an exceptional year as
regards both weather conditions and air pollution. Although the headline indicator had
been showing an overall downward trend in both UK urban and rural areas since theearly 1990s, 2003 showed a sharp rise, due primarily to an increased number of poorozone days. In urban areas, ozone accounted for approximately 70% of the increase overprevious years, with the remainder due to PM10 particles. The increase in the rural
indicator figures was due overwhelmingly to ozone.
The main causes of days of moderate or higher air pollution at urban sites are now ozone
and fine particles (PM10). The number of days caused by ozone pollution has fluctuated inboth rural and urban areas, with no overall trend being evident. As noted previously, theproduction of ozone is strongly influenced by the weather; as a result, the exceptionallyhot, sunny summer in 2003 led to the greatest number of days of moderate or higher
ozone pollution since this modern air quality indicator series began in 1987.
Ozone causes the overwhelming majority of pollution days in rural areas but, since 1999,
it has also caused more days of poor air quality in urban areas than particles or any otherpollutants. Between 1993 and 2002, the average number of days of pollution at urbansites caused by fine particles, solely or in combination with other pollutants, fell from anaverage per site of about 43 days to 6 days per year, but rose again to 17 days in 2003.
UK-wide emissions of particles have declined substantially in recent years, but the
number of pollution days can still fluctuate from year to year due to variations in weather
conditions and the impacts of long-range transport from outside the UK.
Sulphur dioxide, which used to make a significant contribution to the index, has now
fallen to relatively very low levels. Short-term levels of the other two pollutants includedin the index, carbon monoxide and nitrogen dioxide, have very rarely reached moderateor higher levels since 1993. However, long-term exposure to nitrogen dioxide remains a
problem in many parts of the UK; this is why it triggers the declaration of Air Quality
Management Areas in many urban areas with high traffic densities.

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20

21

22

Figure 20- Smoke and SO2 trends over the last 40 years
Figure 21- Number of days of moderate or higher pollution at
urban and rural sites, 1987-2003
Figure 22- Number of days of moderate or higher pollution
caused by the different pollutants, 1992-2003

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Every year, a comprehensive analysis is undertaken of how UK-wide air quality
measurements from the national networks compare with the Air Quality Objectives –boththose established in Regulation (and summarised in Table 1) and those not in Regulation
or of more localised coverage for London and other parts of the country. Results from thelatest such analysis carried out in 2003 are summarised in Figure 23. In this figure, themean compliance statistics, averaged over all measurement sites, are normalised andexpressed as a percentage of that Air Quality Objective. To provide additional
information, the maximum site statistic is also graphed. The height of each yellow bar in
the figure therefore shows how that all-site average statistic in 2002 compares with therelevant national objective, whilst the blue line show how the ‘worst’ site compares withthat objective.
For example, Figure 23 shows that current site-averaged annual average benzo[a]pyrene
levels substantially exceed the relevant 2010 objective of 0.25µg m-3. Similarly, whilst
the overall site-average annual NO2 level is less than the 2005 objective of 40µg m-3,
many sites still exceed this objective, with a maximum of over twice this value. The
figure also shows widespread non-compliance with a range of 2004 and 2010 PM10
objectives. Clearly, there remains cause for concern in relation to levels of thesepollutants.
By contrast, the Objectives for many pollutants- including benzene, 1,3-butadiene, lead,
CO and SO2- are already being met throughout the UK.
It is interesting to examine how the situation now compares with that revealed by similar
analyses undertaken in previous years. Comparisons with corresponding analyses
undertaken in 1997, for instance, demonstrate improvements for all pollutants, andparticularly for PM10. So, although there is no room for complacency, the overall longterm trends for UK-wide levels of most air pollutants continue to show progressive
improvement over time.

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