Authors Christopher Conolly and Hao Wu
Compilation date 2021-03-22
Customer Environment Agency, Department for Environment, Food and Rural Affairs, Department of Environment Northern Ireland, Welsh Government and Scottish Government
Approved by Brian Donovan
Copyright Ricardo Energy & Environment
EULA http://ee.ricardo.com/cms/eula/

Contract reference 23102 Report reference ED62291/PAH2019AR/Issue 1

Executive Summary

This annual report for 2019 for the UK PAH Monitoring and Analysis Network was prepared by Ricardo Energy and Environment for the Environment Agency, the Department for Environment, Food and Rural Affairs, the Department of Environment Northern Ireland, the Welsh Government and the Scottish Government.

During 2019 the number of ambient air sampling sites in the UK PAH network increased from 32 to 33 with the addition of Bristol St Paul’s. The network of two deposition samplers remained unchanged. Most of the sampling locations in the network are urban background, but also includes urban industrial, rural background and a single site that is urban traffic. The rural background sites are located at Chilbolton Observatory, Hampshire and Auchencorth Moss, Midlothian. Results from these two rural background sites are used to support the European Monitoring and Evaluation Programme (EMEP) to Level 2. EMEP is a scientifically based and policy driven programme under the Convention on Long-range Transboundary Air Pollution (CLRTAP) (UNECE, 1979) for international co-operation to solve transboundary air pollution problems.

The UK Polycyclic Aromatic Hydrocarbons (PAH) Monitoring Network comprises non automatic systems to measure PAH in ambient air and deposition. Benzo[a]pyrene (B[a]P) has been identified as a human carcinogen by IARC and has been determined to be a suitable ‘marker’ for the PAH mixture in ambient air.

There is an EU Target Value that relates to the annual mean concentration of Benzo[a]pyrene (1 ng/m3). There is also a more stringent UK National Air Quality Objective for B[a]P in ambient air is an annual mean concentration of 0.25 ng/m3 as detailed in the Air Quality Strategy (Defra, 2007).

Key findings for 2019:

  • In 2019 the EC target value for B[a]P (annual mean concentration of 1 ng/m3) was only exceeded at the Scunthorpe Town site with an annual mean concentration of 1.9 ng/m3.
  • In 2019 ten sites exceeding the UK Air Quality Objective for B[a]P (annual mean concentration of 0.25 ng/m3), these are:
    • Scunthorpe Town
    • Scunthorpe Low Santon
    • Derry/Londonderry Brandywell
    • Port Talbot Margam
    • Royston
    • Ballymena Ballykeel
    • Kilmakee Leisure Centre
    • South Hiendley
    • Ruardean
    • Kinlochleven

In addition to these sites Bristol St Paul’s concentration was above the UK Air Quality Objective for B[a]P however, that site was only operational from the 1st November 2019 so is not considered representative of the full year.

  • The average data capture of all of the operational sites throughout the whole of 2019 was 98%

1 Introduction

This report was prepared by Ricardo as part of the UK PAH Monitoring and Analysis Network (‘the Network’ or ‘the PAH Network’) contract number 23102 with the Environment Agency for the Department for Environment, Food and Rural Affairs, the Northern Ireland Department of Agriculture, Environment and Rural Affairs (DAERA), the Welsh Government and the Scottish Government.

Ricardo assumed full operation of the Network on the 1st of September 2016 following a transition period from the previous contractor. This annual report presents and discusses data from both the current contract and the data reported by the previous contractors since data was collected by the Digitel DHA-80 samplers originally set up by the Ricardo team in the late 2000’s.

This interactive annual report contains:

  • An introduction to polycyclic aromatic hydrocarbons (PAHs)
  • Summary of air quality policy relating to PAHs
  • Information relating to sources of PAHs in the UK
  • A network overview including equipment and details of the sampling locations and changes
  • Summary of analytical techniques employed
  • A comparison of annual mean B[a]P concentrations with the EU Target Value and the more stringent UK Air Quality Objective
  • Monthly PAH concentrations in 2019
  • Review of concentration trends of B[a]P at each of the monitoring sites

The appendices of this report present data for the monthly deposition concentrations of B[a]P at all Network stations that were operational in 2019. However, this information air concentration data and other monthly concentration data for all other PAHs measured within the network can be accessed via the UK-AIR website.

1.1 Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutant compounds they contain two or more benzene rings, they are generally produced through incomplete combustion or pyrolysis.

The International Agency for research on Cancer (IARC) has determined that B[a]P is carcinogenic to humans and is currently considered by IARC as the most carcinogenic PAH. Details of the assessment of the carcinogenicity of PAHs carried out by IARC can be found online.

Table 1 below shows the details of PAH that are required to be measured under the Fourth Daughter Directive (2004/107/EC) (EC, 2005) in the UK, plus benzo[ghi]perylene which was more recently included in the 2014 technical standard CEN/TS 16645:2014 (BSI, 2014).

Table 1: PAH structures of PAH that should be monitored according to the 4th Daughter Directive (2004/107/EC). The IARC Carcinogenic Classification of PAH can be found on the IARC website.

Compound Structure
Benz[a]anthracene
Benzo[b]fluoranthene
Benzo[j]fluoranthene
Benzo[k]fluoranthene
Benzo[a]pyrene
Dibenz[a,h]anthracene
Indeno[1,2,3-cd]pyrene
Benzo[g,h,i]perylene

1.2 Air Quality Policy

In the UK there is a national air quality objective for B[a]P in ambient air, based on an annual mean concentration of 0.25 ng/m3. Details can be found in the UK Air Quality Strategy (Defra, 2007).

The EC Air Quality Framework Directive (Directive 96/62/EC) (EC, 1996) set a strategic framework to tackle air quality in a consistent way across Europe by setting limit and target values for air pollutants via a series of Daughter Directives. The Fourth Daughter Directive sets a target value for B[a]P of 1 ng/m3 (total content in the PM10 fraction averaged over a calendar year). Mandatory measurement requirements relating to the measurement of B[a]P can be found in the Fourth Daughter Directive (Directive 2004/107/EC).

B[a]P’s suitability as a marker for the PAH mixture in ambient air as stated in the EC Position Paper on PAH (EC, 2001) led to it being selected as the measure for monitoring in the Fourth Daughter Directive (Directive 2004/107/EC) and the more stringent UK National Air Quality Objective for PAH (annual mean of 0.25 ng/m3 B[a]P in ambient air). Measurements of B[a]P in ambient air are covered by the European standard EN 15549 (BSI, 2008), which has been adopted as the European reference method.

Measurements of PAH in deposition are covered by European standard EN 15980 (BSI, 2011) which details the measurement method sampling, sample preparation and analysis for benz[a]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene and indeno[1,2,3-cd]pyrene. There is no limit or target value related deposition of PAH in the UK or Europe.

The two rural background sites located at Chilbolton Observatory, Hampshire and Auchencorth Moss, Midlothian are used to support the European Monitoring and Evaluation Programme (EMEP) to Level 2. EMEP is a scientifically based and policy driven programme under the Convention on Long-range Transboundary Air Pollution (CLRTAP) which was signed by the UK in 1979. The convention aids international co-operation to solve transboundary air pollution problems, provides access to emission, measurement and modelling data and provides information on the effects of air pollution on ecosystems, health, crops and materials.

1.3 Sources of PAHs in the UK

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutant compounds. They contain two or more benzene rings, they are generally produced through incomplete combustion or pyrolysis. The National Atmospheric Emissions Inventory (NAEI) has estimated the emission of PAH for the UK for many years. The inventory estimates the emissions of PAHs including benzo[a]pyrene. As with all emissions inventories there is some uncertainty in the estimates as the emissions are not based solely on measurements and require some estimation of emission factors and activities being required.

In recent years the Inventory indicates that residential and commercial combustion are the dominate emission sources of B[a]P in the UK. Defra’s Clean Air Strategy reports that the used of wood as a domestic fuel has been calculated to produce 78% of total national emission of Benzo[a]pyrene (B[a]P). More information relating to UK Emissions of PAH and other pollutant can be accessed via the NAEI website.

2 The PAH Network

2.1 Network Objectives

The objective of the PAH Network is to determine the ambient concentrations of PAHs in ambient air in the UK through monitoring and chemical analysis, and deliver or aid the delivery the following:

  • A UK assessment of current concentrations of PAHs for assessment against the Fourth Daughter Directive and the UK Air Quality Strategy objectives, and provide measurement input for any future reviews.
  • A Review of the measurements and trends of airborne concentrations of PAHs in representative UK industrial, urban and rural locations.
  • Provide data and metadata to UK-AIR to enable demonstration of the UK’s compliance with the Fourth Daughter Directive, the OSPAR convention (OSPAR, 2017) and the UNECE Convention on Long Range Transboundary Air Pollutants (UNECE, 1979), to enable a better understanding of sources or potential sources of PAH.

2.2 Network Overview

The 33 monitoring stations operating in the UK PAH Network during 2019 are shown in Figure 1. Two monitoring sites where both Digitel particulate samplers and deposition samples are taken are marked with the drop marker (Auchencorth Moss and Chilbolton Observatory). Other sites where only Digitel particulate samples are taken are marked with red circles.

Figure 1: Map of UK PAH monitoring stations in 2019.


In 2019 there were 33 ambient air sampling sites operational in the network in the UK in addition to two deposition samplers. The majority of the sampling locations are urban background, but the network also includes urban industrial, two rural background sites located at Chilbolton Observatory, Hampshire and Auchencorth Moss, Midlothian and a single urban traffic site at London Marylebone Road. The rural background sites are used to support the European Monitoring and Evaluation Programme (EMEP).

2.3 Samplers in the PAH Network

The Network requires the sampling and analysis of two types of samples these are particulate and deposition samples.

‘PAH Digitel (solid phase)’ particulate samplers. These samples are in the PM10 fraction of ambient air on a filter and are taken daily at all network stations using Digitel DHA-80 samplers with automatic filter changers. Each sample is taken for 24 hours with the sample changeover occurring at midnight (GMT). The samples are bulked into groups representing calendar months per location for analysis. The Digitel DHA-80 samplers (see Figure 2) used throughout the Network are considered to be equivalent to the requirements of the European Standard for sampling PM10 matter (EN 12341) (BSI, 2014). The samplers are therefore valid for use with the European Standard method for the measurement of B[a]P in ambient air (EN 15549). The solid phase filter samples have a measurement period of 24 hours at a flowrate of approximately 30 m3/h.

Figure  2: Digitel DHA-80 sampler deployed to measure solid phase PAH in the UK Network.

Figure 2: Digitel DHA-80 sampler deployed to measure solid phase PAH in the UK Network.

‘PAH deposition’ samplers. These deposition samples are taken fortnightly at two rural stations within the network at Auchencorth Moss and Chilbolton Observatory (prior to 2016 the equipment at Chilbolton was located at Harwell). Each sample is taken for 14 days using a deposition sampler (Figure 3) that meets the requirement of the European Standard for the measurement of the deposition of PAHs (EN 15980). The deposition samplers itself consist of a glass funnel and a four litre brown glass collection bottle, which are located inside a protective tube in order to minimise photochemical reactions and the degradation of PAHs. The spikes seen on the image have been fitted to the top of the protective tubes to prevent damage and contamination by bird strikes.

Figure  3: Samplers to measure deposition of PAH in the UK Network.

Figure 3: Samplers to measure deposition of PAH in the UK Network.

2.3.1 Sampling Quality Control

To ensure the quality of the sampling procedure there are a number of checks and quality assurance and quality control measures that are undertaken on the data and the filters used in the samplers prior to use. These include the inspection of sampling media prior to use at sampling sites, analysis of field and sample blanks, checking of equipment operation via online systems, review of the measurement data associated with the filters being returned from the sites to ensure they meet the requirement of the EN 15549 standard. In addition to these checks the network is supported by an infrastructure of local site operators who are fully trained and provided with detailed working instructions for site operation.

2.4 Network Activities During 2019

2.4.1 Station Infrastructure and Network Re-organisation

The following network infrastructure changes took place which are not detailed in previous reports covering the time period at the end of 2015 and 2019:

  • Hove PAH sampling ceased 31st December 2015
  • London Crystal Palace Parade PAH sampling ceased 31st December 2015
  • Nottingham Centre PAH sampling began 16th November 2016
  • Ruardean PAH sampling began 15th March 2017
  • Sheffield Tinsley PAH sampling began 16th March 2017
  • Birmingham Tyburn PAH sampling ceased 24th May 2017
  • Newport PAH sampling suspended from 16th August 2017 to 6th April 2018 due to safety work at the monitoring site
  • Birmingham Ladywood PAH sampling began 1st June 2018
  • Scunthorpe Santon PAH sampling suspended from 9th September 2020 to 22nd October 2019 due to roof replacement
  • Bristol St Paul’s PAH sampling began 1st November 2019

2.4.2 Data capture, Station Calibrations, Services and Breakdowns

All Stations were calibrated and serviced in 2019 and checks on flow were undertaken. Table 2 below shows the data captures for 2019.

Table 2: PAH data capture in 2019.
Site Data capture
Auchencorth Moss 95%
Ballymena Ballykeel 99%
Birmingham Ladywood 99%
Bolsover 99%
Bristol St Paul’s* 16% (95% for the operational period)
Cardiff Lakeside 99%
Chilbolton Observatory 99%
Derry Brandywell 98%
Edinburgh St Leonards 99%
Glasgow Townhead 99%
Hazelrigg 99%
High Muffles 97%
Kilmakee Leisure Centre 100%
Kinlochleven 95%
Leeds Millshaw 100%
Liverpool Speke 97%
London Brent 100%
London Marylebone Road 97%
Lynemouth 2 99%
Middlesbrough 99%
Newcastle Centre 98%
Newport 96%
Nottingham Centre 98%
Port Talbot Margam 99%
Royston 98%
Ruardean 98%
Salford Eccles 99%
Scunthorpe Low Santon* 84%
Scunthorpe Town 96%
Sheffield Tinsley 100%
South Hiendley 94%
Stoke Ferry 98%
Swansea Cwm Level Park 96%
Network Average (excluding Bristol St Paul’s) 98%
*Site not operating for part of the year due to safety concerns (Scunthorpe Santon) or or not installed for the full year (Bristol St Paul’s).


All sites that were in place at the start of 2019 have data captures of above 95% with the exception of Scunthorpe Santon, which had site structure safety repairs which led to the sampler at the site being switched off. The Scunthorpe Santon site had still achieved a data capture of 84% despite this issue. The network average data capture for sites operating from the start of 2019 including the Scunthorpe Santon sites was 98%. This is in line with the recent years where Ricardo have managed the network.

3 Analytical Techniques and PAH reported

In 2019 there was a transition from one analytical laboratory, Concept Life Sciences (CSL) to TNO (Netherlands Organisation for Applied Scientific Research). The analytical method used to analyse for PAH in both sampling media is Gas chromatography–mass spectrometry (GC-MS). The PAH analysed and reported from deposition and particulate samples, typical detection limits and accreditation information for CSL and TNO are shown in Appendix 2 and 3 respectively (Tables A2 and A3).

More information relating to the quality control measures that are undertaken in relation to the analytical work are shown in Appendix 2 and 3.

4 Results & Discussions

This section presents and discusses the results from the PAH Digitel (solid phase) particulate samplers’ stations. The discussion focuses on B[a]P as the Fourth Daughter Directive Target Values and UK Air Quality Objective both use B[a]P as the marker for the PAH mixture in ambient air. Some data for other PAHs are also presented below. Data for all PAHs for all stations are made available on the UK-AIR website.

4.1 Comparison of B[a]P annual concentrations against EC target values and UK Air Quality Objective

The annual mean B[a]P concentration measured at all the PAH Digitel (solid phase) particulate samplers are shown in Figure 4.

Figure 4: Comparison of annual B[a]P concentrations at all the monitoring stations against EC and UK target values and UK Air Quality Objective.


Only a single site in the UK PAH Network measurement sites exceeded the EC target value of 1 ng/m3 this was Scunthorpe Town with a concentration of 1.91 ng/m3. Three sites exceeded upper assessment threshold (UAT) of 0.6 ng/m3 these were Scunthorpe Town (1.91 ng/m3), Derry Brandywell (0.82 ng/m3) and Scunthorpe Low Santon (0.76 ng/m3). A further site exceeded the lower assessment threshold (LAT) of 0.4 ng/m3 these were Ballymean Ballykeel (0.44 ng/m3). The Bristol St Paul’s site’s concentraton was also above the lower assessment threshold at 0.5 ng/m3, however as it was only measuring PAH from November onwards it is not considered representative of the full year.

The more stringent UK Air Quality Objective for PAH (0.25 ng/m3 B[a]P) was exceeded at ten sites:

  • Scunthorpe Town
  • Scunthorpe Low Santon
  • Derry/Londonderry Brandywell
  • Port Talbot Margam
  • Royston
  • Ballymena Ballykeel
  • Kilmakee Leisure Centre
  • Ruardean
  • South Hiendley
  • Kinlochleven

Whilst some of the above sites have specific emission sources such as steel works (Scunthorpe sites and Port Talbot Margam), other urban sites may have solid fuel/wood use contributing to their exceedance of the UK Air Quality Objective for PAH.

4.2 B[a]P monthly concentrations

PAH are expected to show seasonality with the higher concentrations observed during the winter months as a result of domestic and industrial combustion processes usually related with heating during the colder months. Industrial sites would generally be expected to show less seasonality as any seasonality related to such domestic and industrial combustion process for heating would be masked by the more constant emissions from industrial processes. The monthly concentrations of B[a]P for 2019 grouped by the site characteristic types are shown in Figure 5 - 9.

4.2.1 Northern Ireland sites

Figure 5: Monthly average B[a]P concentrations at the Northern Ireland sites and average regional temperatures in 2019.

The Monthly variation of B[a]P concentrations in Northern Ireland for 2019 continued to show pronounced seasonal variation with low concentrations in the summer months and higher in winter. The above figure shows that when lower temperatures are observed there is an increase in B[a]P. This supports the understanding that the PAH sites in Northern Ireland are highly influenced by emission from solid fuel usage for domestic heating.

The lower boundary layer depth in the winter months also contributes to the increased concentrations in the winter months. The boundary layer (often called the Atmospheric Boundary Layer) is the layer of atmosphere next to the surface of the earth. Within this layer air is very well mixed. If the boundary layer decreases in height, as is common in winter months this can increase concentrations within the layer.

4.2.2 GB urban background

Figure 6: Monthly average B[a]P concentrations at urban background sites in GB in 2019.

Urban background sites in Great Britain generally exhibited seasonal variability resulting from the anticipated solid fuel usage. Whilst this isn’t as pronounced as the Northern Ireland sites there is still an observed decrease in concentrations during the summer months. At the majority of the urban sites there is an elevation in concentrations observed in November which like in previous years is likely to be a combination between solid fuel use and the effect of Guy Fawkes Night.

4.2.3 GB rural background

Figure 7: Monthly average B[a]P concentrations at rural background sites in GB in 2019.

The Ruardean site has the highest concentration of the rural sites and shows a seasonal profile that is more pronounced than the other rural sites. This is likely to be due to the site being located within the village. The other sites of Chilbolton and Stoke Ferry also have local influences being close to small villages that could potentially contribute to PAH concentrations particularly during the winter months.

The most rural site in the PAH network is considered to be Auchencorth Moss (red line), it is not thought that this site is influenced significantly by any local sources or by industry and would be the best site to represent the PAH concentration of regional background.

The rural PAH network sites show much lower concentrations throughout the year than most of the urban and industrial sites. However, there is seasonality observed at the sites. The ‘Guy Fawkes Night effect’ does not appear to be as prominent at the rural locations where PAH are measured but it is present at some sites.

4.2.4 GB industrial

Figure 8: Monthly average B[a]P concentrations at operating industrial sites and those that are now closed in 2019.

These monitoring sites are likely to be influenced by the nearby industrial activities, which are relatively invariant throughout the year, therefore, seasonality is less pronounced.

The sites that are still influenced by industry are Port Talbot Margam, Scunthorpe Town and Scunthorpe Low Santon. These sites show limited seasonality due to the seasonal sources that may be present such as for domestic heating are masked by the more consistent and dominating industrial emissions at these locations. Industrial sources are more likely to deviate from the usual seasonal patterns seen with PAH concentrations as relatively high concentrations are observed during non-winter months as well as the winter months.

The industrial sites that do show seasonality are the sites where the local industrial PAH sources have closed. These are Lynemouth, Middlesbrough, South Hiendley and Royston. These site may be influenced by emission from domestic heating emission from solid fuel in addition the lower boundary layer depth in the winter months also contributes to the increased concentrations.

The Scunthorpe town site has two peaks in concentration of benzo[a]pyrene in April and November 2019. The exceedance was considered likely to be as a result of pressure relief systems causing increased emissions from Coke Oven Plant in April and November and due to prevailing wind speed and directions transporting these emissions from the nearby regulated industry integrated steelworks in the direction of the Scunthorpe Town monitoring site.

4.2.5 GB urban traffic

Figure 9: Monthly average B[a]P concentrations at the urban traffic site in GB in 2019.


Marylebone road is the only urban traffic site that measures PAH and is a site that has significant traffic flow. There is a clear seasonality observed at the site and the magnitude of B[a]P measured at Marylebone road is comparable to that measured at other urban background sites in Great Britain. This could indicate that the concentrations of B[a]P at the site may not dominated by traffic even though the site is a traffic site and could indicate that it is as a result of seasonal emissions relating to domestic and other heating emissions. There is also a slight elevation in concentrations in November in 2019 which is smaller than at other urban background sites it is possible that that could be attributed to Guy Fawkes Night.

4.3 Other PAHs Monthly Concentrations

As detailed earlier in this report the Fourth Daughter Directive also specifies that six other PAHs should be monitored at a limited number of measurement stations. The PAH the directive refers to are benz[a]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, indeno[1,2,3-cd]pyrene, and dibenz[a,h]anthracene. The CEN TC264 WG21 developed a Technical Specification for the measurement of these PAHs and benzo[ghi]perylene in the particulate phase. The UK PAH Network measures all of the PAH referred to in the Technical Specification at all stations and since Ricardo Energy & Environment took over the network from the previous contractor, these have been analysed and reported separately. The monthly mean concentration of each of these PAHs measured at the sites are shown in the figures below. On a review of the figures on a visual basis only, these PAH appear to follow similar seasonal trends to those of the ‘marker’ B[a]P, which indicates that the assumptions made in using B[a]P as a marker are well founded.

4.3.1 Benz[a]anthracene

Figure 10: Monthly mean benz[a]anthracene concentrations at the UK PAH sites.

4.3.2 Benzo[b]fluoranthene

Figure 11: Monthly mean benz[b]fluoranthene concentrations at the UK PAH sites.

4.3.3 Benzo[j]fluoranthene

Figure 12: Monthly mean benzo[j]fluoranthene concentrations at the UK PAH sites.

4.3.4 Benzo[k]fluoranthene

Figure 13: Monthly mean benzo[k]fluoranthene concentrations at the UK PAH sites.

4.3.5 Indeno[1,2,3-cd]pyrene

Figure 14: Monthly mean indeno[1,2,3-cd]pyrene concentrations at the UK PAH sites.

4.3.6 Dibenz[ah]anthracene

Figure 15: Monthly mean dibenz[a,h]anthracene concentrations at the UK PAH sites.

4.3.7 Benzo[ghi]perylene

Figure 16: Monthly mean benzo[ghi]perylene concentrations at the UK PAH sites.

4.4 Depositon (‘C’) samples

The 4 weekly bulked samples of Benzo[a]pyrene concentrations measured in deposition at the Auchencorth Moss and Chilbolton sites are displayed in Appendix 1. The levels of PAH at these rural sites in the UK are very low as reported in the previous annual reports. The levels found are often below or very close to detection limits, which makes any interpretation of the data difficult. Other PAH analysed are also regularly below detection limits. The monitoring conducted at the sites does however enable the UK to meet its obligations under the Forth Daughter Directive. All deposition data is available on the UK-AIR website.

4.6 Trend Assessment at the UK PAH Network sites

To summarise the long-term each at each monitoring site, the slope of the trend for each site was calculated using TheilSen function in the openair R package (Figure 22). A positive slope means that there is an increasing trend of B[a]P annual mean and a negative slope means a decreasing trend. The slope of each site’s B[a]P concentration over time was also calculated with its 95% confidence interval, which indicates the uncertainty of the slope coefficient. If the uncertainty of the slope covers zero, it suggests that no significant trend can be concluded. Figure 22 shows separately the sites that had a significant trend and the sites that did not. It should be noted that sites which have not been installed for very long have not been included due to the limited number of data points, the sites affected are: Bristol St Paul’s, Chilbolton, Nottingham and Ruardean.

Figure  22: B[a]P concentration trend (ng m^-3^ yr^-1^) from 2008 to 2019.

Figure 22: B[a]P concentration trend (ng m-3 yr-1) from 2008 to 2019.


The trend calculated from many of the monitoring sites did not show a significant decreasing or increasing trend. This was either because there was very little change in the annual concentrations (i.e. a slope was not significantly different from zero) or there were large variations between years but not in a consistent direction (as indicated by the large confidence intervals (red bars) at the two Scunthorpe sites). For all the sites where a significant trend was observed, they generally showed a very small decreasing trend and the sites showing large decreasing trend (South Hiendley, Royston and Ballymena Ballykeel) were associated with larger uncertainties but all appear to have a significant decreasing trend in B[a]P concentrations.

5 Conclusions

The average data capture of all of the sites that were operational throughout 2019 was 98%. The annual mean Benzo[a]pyrene concentrations observed at the UK networks during 2019 continued to vary greatly between sites. The highest annual mean was observed at the Scunthorpe Town site with an annual mean B[a]P concentration of 1.91 ng/m3 and the lowest concentration measured at the Auchencorth Moss site 0.01 ng/m3.

In 2019 the EU Target Value for B[a]P (annual mean concentration of 1 ng/m3) was exceeded at Scunthorpe Town Site. The exceedance was considered likely to be as a result of pressure relief systems causing increased emissions from Coke Oven Plant in April and November and due prevailing wind speed and directions transporting these emissions from the nearby regulated industry integrated steelworks in the direction of the Scunthorpe Town monitoring site.

In 2019 eight sites exceeding the UK Air Quality Objective for B[a]P (annual mean concentration of 0.25 ng/m3) these were Ballymena Ballykeel, Derry/Londonderry Brandywell, Kilmakee Leisure Centre, Kinlochleven, Port Talbot Margam, Royston, Scunthorpe Low Santon Scunthorpe Town, South Hiendley and Ruardean.

The levels of B[a]P have been seen to be decreasing at sites where industrial sources have ceased operating and also at a number of the urban sites most prominent at Ballymena Ballykeel.

References

BSI, 2014. BS EN 12341:2014 Ambient air. Standard gravimetric measurement method for the determination of the PM10 or PM2.5 mass concentration of suspended particulate matter.

BSI, 2011. BS EN 15980:2011 Air quality. Determination of the deposition of benz[a]Anthracene, benzo[b]Fluoranthene, benzo[j]Fluoranthene, benzo[k]Fluoranthene, benzo[a]Pyrene, dibenz[a,h]Anthracene and indeno[1,2,3-cd]Pyrene.

BSI, 2008. Air quality. Standard method for the measurement of the concentration of benzo(a)Pyrene in ambient air. BS EN 15549:2008.

Defra, 2007. The Air Quality Strategy for England, Scotland, Wales and Northern Ireland (Volume 1). URL https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69336/pb12654-air-quality-strategy-vol1-070712.pdf (accessed 2-June-2017).

EC, 2005. Directive 2004/107/EC of the European Parliament and of the Council of 15 December 2004 relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air. URL http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32004L0107\&from=EN (accessed 26-July-2017).

EC, 2001. Ambient air pollution by Polycyclic Aromatic Hydrocarbons (PAH). Position Paper. URL http://ec.europa.eu/environment/air/pdf/pp_pah.pdf (accessed 26-July-2017).

EC, 1996. Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management. URL http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:31996L0062\&from=EN (accessed 26-July-2017).

OSPAR, 2017. The Convention for the Protection of the Marine Environment of the North-East Atlantic.

UNECE, 1979. 1979 Convention on long-range transboundary air pollution.

Appendix 1 PAH Deposition

Table A1: PAH deposition for B[a]P in 2019.
Station name Start date End date Measurement (ng/m2/day)
Auchencorth Moss 02/01/2019 30/01/2019 <90
Auchencorth Moss 30/01/2019 27/02/2019 <90
Auchencorth Moss 27/02/2019 27/03/2019 <90
Auchencorth Moss 27/03/2019 24/04/2019 <90
Auchencorth Moss 24/04/2019 22/05/2019 <90
Auchencorth Moss 22/05/2019 19/06/2019 4
Auchencorth Moss 19/06/2019 17/07/2019 5
Auchencorth Moss 17/07/2019 14/08/2019 4
Auchencorth Moss 14/08/2019 11/09/2019 3
Auchencorth Moss 11/09/2019 09/10/2019 7
Auchencorth Moss 09/10/2019 06/11/2019 4
Auchencorth Moss 06/11/2019 04/12/2019 3
Auchencorth Moss 04/12/2019 02/01/2020 2
Chilbolton Observatory 02/01/2019 30/01/2019 <90
Chilbolton Observatory 30/01/2019 27/02/2019 <90
Chilbolton Observatory 27/02/2019 27/03/2019 <90
Chilbolton Observatory 27/03/2019 24/04/2019 <90
Chilbolton Observatory 24/04/2019 22/05/2019 <90
Chilbolton Observatory 22/05/2019 19/06/2019 7
Chilbolton Observatory 19/06/2019 17/07/2019 12
Chilbolton Observatory 17/07/2019 14/08/2019 8
Chilbolton Observatory 14/08/2019 11/09/2019 10
Chilbolton Observatory 11/09/2019 09/10/2019 11
Chilbolton Observatory 09/10/2019 06/11/2019 7
Chilbolton Observatory 06/11/2019 04/12/2019 6
Chilbolton Observatory 04/12/2019 31/12/2019 3

Appendix 2 Concept Life Science PAH Analysis January - April 2019

Table A2: PAH analysed in Deposition and particulate samples and their typical detection limits (all ISO 17025 Accredited).
Deposition samples Particulate samples
PAH Analysed Typical LOD ng/m2/day Analysed Typical LOD ng/m3
5-Methyl Chrysene Yes 285 Yes 0.0046
9-Methyl anthracene Yes 190 Yes 0.0046
Acenaphthene Yes 190 Yes 0.0046
Benzo(a)Pyrene Yes 190 Yes 0.0046
Benzo(b)fluoranthene Yes 190 Yes 0.0046
Benzo(b)naphtho(2,1-d)thiophene Yes 190 Yes 0.0046
Benzo(c)phenanthrene Yes 190 Yes 0.0046
Benzo(e)pyrene Yes 190 Yes 0.0046
Benzo(ghi)Perylene Yes 190 Yes 0.0046
Benzo(j)fluoranthene Yes 190 Yes 0.0046
Benzo(k)fluoranthene Yes 190 Yes 0.0046
Cholanthrene Yes 190 Yes 0.0046
Chrysene Yes 190 Yes 0.0046
Coronene Yes 190 Yes 0.0046
Cyclopenta(c,d)pyrene Yes 190 Yes 0.0046
Dibenzo(ae)pyrene Yes 190 Yes 0.0046
Dibenzo(ah)pyrene Yes 190 Yes 0.0046
Dibenzo(ai)pyrene Yes 190 Yes 0.0046
Dibenzo(al)pyrene Yes 190 Yes 0.0046
Dibenzo(ac)anthracene* Yes 190 Yes 0.0046
Dibenzo(ah)Anthracene* Yes 190 Yes 0.0046
Indeno(1,2,3-cd)pyrene Yes 190 Yes 0.0046
Perylene Yes 190 Yes 0.0046
2-Methyl naphthalene Yes 190 No -
2-Methyl phenanthrene Yes 190 No -
4.5-Methylene phenanthrene Yes 190 No -
Acenaphthylene Yes 190 No -
Anthanthrene Yes 190 No -
Anthracene Yes 190 No -
Benzo(a)Anthracene Yes 190 No -
Benzo(b+j)fluoranthene* Yes 190 Yes 0.0046
Biphenyl Yes 190 No -
Dibenzo(ah+ac)anthracene* Yes 190 Yes 0.0046
Fluoranthene Yes 190 No -
Fluorene Yes 190 No -
Naphthalene Yes 190 No -
Phenanthrene Yes 285 No -
Pyrene Yes 190 No -
Retene Yes 285 No -

Concept Life Sciences (CSL) (previously known as Scientific Analysis Laboratories) were the chosen analytical laboratory for the UK PAH network from when Ricardo took over the network until the end of April 2019 when TNO took over the analysis (for details see Appendix 3).

Concept Life Sciences are an ISO 17025 accredited laboratory for the analysis of PAH in the samples from the PAH network. The procedure used to measure PAH in ambient air sampled on filters and deposition samples is Gas chromatography mass spectrometry (GC/MS). The performance of this method is validated in accordance with internationally recognised procedures and meet the requirement for PAH analysis detailed in the standards for the measurement of PAH in ambient air and deposition (EN15549:2008 and EN15980:2011 respectively). PAH and typical detection limits for the analysis in the PAH network are presented in Table A2 above.

Ambient air, sampled on to GF/A filters, are bulked into monthly batches with a specific portion extracted in dichloromethane with the use of ultra-sonication. The dichloromethane is then reduced to circa 1 ml prior to analysis by GC/MS in selected ion monitoring mode (SIM).

Deposition samples are initially filtered to separate any particulate content from the aqueous phase. The filters are then extracted in dichloromethane with the use of ultra- sonication, while the aqueous phase is liquid/liquid extracted with dichloromethane. The organic fractions are then combined, reduced to circa 1 ml and analysed by GC/MS in Selected ion monitoring mode (SIM).

In addition to the Performance Expectations of ISO 17025 accredited analytical laboratory the following analytical quality control measures are undertaken to maintain analytical quality:

  • Multi-point calibration with authentic standards. The calibration fit should be linear, with a typical correlation coefficient of R2 > 0.995
  • Analysis of QC samples within each analytical batch
  • An independent calibration check standard is analysed at the start and end of each batch to confirm the calibration has been prepared correctly and there has been minimal or no drift throughout the run
  • Resolution and peak asymmetry checks are performed
  • Analysis of reagent/method blanks within each analytical batch.
  • Ongoing quality assured by the use of control charts in conjunction with warning and action limits for the QC sample data
  • Participation in external proficiency testing and inter-laboratory schemes such as LGC CONTEST and AQUACHECK for system performance

Appendix 3 TNO PAH Analysis May to December 2019

TNO were the chosen analytical laboratory for the UK PAH network from May 2019 analysis forward. TNO are an ISO 17025 accredited laboratory for the analysis of PAH in the samples from the PAH network. The procedure used to measure PAH in ambient air sampled on filters and deposition samples is Gas chromatography mass spectrometry (GC/MS). The performance of this method is validated in accordance with internationally recognised procedures and meet the requirement for PAH analysis detailed in the standards for the measurement of PAH in ambient air and deposition (EN15549:2008 and EN15980:2011 respectively).

TNO undertake national PAH analysis in the Netherlands and take part in international inter-comparisons including those run annually by INERIS (the French National Institute for Industrial Environment and Risks).

PAH and typical detection limits for the analysis in the PAH network are presented in Table A3 below.

Table A3: PAH analysed by TNO in Deposition and particulate samples and their typical detection limits.
Deposition samples Particulate samples
PAH ISO 17025 accredited Typical LOD ng/m2/day Typical LOD ng/m3
Benzo(a)antracene Yes 0.19 to 0.26 0.00004 to 0.00056
Cyclopenta(c,d)pyrene No 0.28 to 0.38 0.00004 to 0.00056
Chrysene Yes 0.20 to 0.26 0.00004 to 0.00056
5-methylchrysene No 0.34 to 0.47 0.00004 to 0.00056
Benzo(b)fluorantene Yes 0.22 to 0.28 0.00004 to 0.00056
Benzo(k)fluorantene Yes 0.23 to 0.30 0.00004 to 0.00056
Benzo(j)fluorantene No 0.24 to 0.31 0.00004 to 0.00056
Benzo(e)pyrene No 0.23 to 0.30 0.00004 to 0.00056
Benzo(a)pyrene Yes 0.23 to 0.32 0.00004 to 0.00056
Indeno(123-cd)pyrene Yes 0.18 to 0.27 0.00004 to 0.00056
Dibenzo(ah)antracene Yes 0.27 to 0.37 0.00004 to 0.00056
Denzo(ghi)perylene Yes 0.27 to 0.37 0.00004 to 0.00056
Dibenzo(al)pyrene No 0.46 to 0.59 0.00004 to 0.00056
Dibenzo(ae)pyrene No 0.41 to 0.52 0.00004 to 0.00056
Denzo(ai)pyrene No 0.81 to 1.23 0.00004 to 0.00056
Dibenzo(ah)pyrene No 0.57 to 0.87 0.00004 to 0.00056


For further information, please contact:

Name Christopher Conolly
Address Ricardo Energy & Environment, Gemini Building, Harwell, Didcot, OX11 0QR, United Kingdom
Telephone 01235 753375
Email christopher.conolly@ricardo.com