1.1 Background

Jersey is the largest of the Channel Islands at 45 square miles, with an estimated population 103,650 ². Both air and sea transport links to the UK and France make it easy to travel to nearby destinations in less than an hour.

This report describes a programme of air quality monitoring carried out on the island of Jersey in 2024, undertaken by Ricardo, on behalf of Jersey Government’s Department of Infrastructure and Environment. The report presents and summarises the fully validated and quality controlled dataset for the period 1^st January to 31^st December 2024. This is the 26^th consecutive year in which an annual monitoring programme has been carried out; the first was undertaken in 1997. This ongoing monitoring programme has provided a long-term dataset of pollutant concentrations.

The pollutants monitored in 2024 were nitrogen dioxide (NO₂), particulate matter (PM₁₀ and PM_2.5) and a range of hydrocarbon species (benzene, toluene, ethylbenzene and two xylene compounds). NO₂ was measured by an automatic monitor, situated at Beresford Street located next to the Central Market in St Helier. This was supplemented by indicative monitoring of NO₂ using low-cost passive samplers (Palmes type diffusion tubes) measured at 23 monitoring locations. Between March 2023 and July 2024, two additional temporary diffusion tube monitoring locations were added to the network to assist in the monitoring of pollutant concentrations during the School Street Pilot Scheme that took place in 2023. Particulate matter concentrations were measured by two automatic monitors, located at Central Market and Howard Davis Park. The suite of hydrocarbon species were monitored using ‘BTEX’ diffusion tubes at five sites during the year.

This report presents the 2024 air quality monitoring results and compares the data from Jersey with relevant air quality limit values, objectives and guidelines as well as data from selected UK monitoring stations and monitoring programmes from prior years.

Data in the annual report have been processed according to the rigorous quality assurance and quality control procedures used by Ricardo. These ensure the data are reliable, accurate and traceable to UK national measurement standards.

In addition to this report, Jersey has daily access to provisional data from its monitoring sites via their own air quality monitoring page ³ and data from the UK’s national air quality monitoring network, through the Defra UK Air Information Resource (UK-AIR) ⁴. Data is also available via Ricardo’s Jersey Air web page ⁵.

1.2 Aims and Objectives

Air quality monitoring during 2024 is the continuation of a survey that has been carried out since 1997. This report is the latest in a series of annual reports. As in previous years, the objective of this report was to monitor at sites where pollutant concentrations were expected to be high and compare these with background locations. The monitoring sites consisted of urban and rural background sites, in addition to locations where higher pollutant concentrations might be expected, such as roadside and kerbside sites, as well as locations close to specific emission sources (for example, a petrol station).

The results of the monitoring are used to assess whether applicable national air quality objectives have been met, and how pollutant concentrations in the area have changed over time.

1.3 Impact of Covid-19 Restrictions on Monitoring

2020 and 2021 saw severe disruption to daily life for all of the world and Jersey was no different. The timeline of events relating to restrictions as a result of the COVID-19 Pandemic and the impacts this had on tourism in Jersey have been described in previous reports within this series. These reports also explained the disruption to the monitoring programme, mainly relating to deployment and collection of diffusion tubes.

In 2024 there were over 1 million arrivals by air and sea combined ⁶. This is an increase of 3% compared to total arrivals to Jersey in 2023. This upward trend shows that Jersey is continuing to recover from the effects of the COVID-19 Pandemic, although air and sea arrivals approximately 16% lower than those experienced in 2019 (Pre-COVID-19).

2.1 Pollutants Monitored

2.2 Air Quality Limit Values and Objectives

This report compares the results of the monitoring survey with air quality limit values and objectives applicable worldwide, in Europe and the UK.

2.3 Monitoring Sites and Methods

2.3.2 Diffusive Sampling of NO₂ and Hydrocarbons

The automatic monitoring site of Beresford Street Market was supplemented by indicative monitoring, using diffusion tubes, for NO₂ and BTEX hydrocarbons. Diffusion tubes are ‘passive’ samplers, i.e. they work by absorbing the pollutants direct from the surrounding air and need no power supply. They are located in places and heights of relevant exposure, usually attached to lampposts at approximately 2m-4m above ground.

2.3.2.1 NO₂ Diffusion Tubes

Palmes-type diffusion tubes were used for NO₂. These consist of a small plastic tube, approximately 7 cm long. During sampling, one end is open and the other closed. The closed end contains an absorbent for the gaseous species (in this case NO₂) to be monitored. The tube is mounted vertically with the open end at the bottom. Ambient NO₂ diffuses up the tube during exposure and is absorbed as nitrite. The average ambient pollutant concentration for the exposure period is calculated from the amount of pollutant absorbed.

Figure 1: NO₂ diffusion tube

2.3.2.2 BTEX Diffusion Tubes

BTEX diffusion tubes are different in appearance from NO₂ tubes. They are longer, thinner, and made of metal rather than plastic. These tubes are fitted at both ends with brass Swagelok fittings. A separate ‘diffusion cap’ is supplied. Immediately before exposure, the Swagelok end fitting is replaced with the diffusion cap. The cap is removed after exposure and is replaced with the Swagelok fitting. BTEX diffusion tubes are very sensitive to interference by solvents.

Figure 2: BTEX diffusion tube

2.3.2.3 Preparation and Analysis

Diffusion tubes were prepared and analysed by Gradko International Ltd. They were supplied to Jersey Government’s Natural Environment Technical Officers, who carried out the tube changing. The tubes were supplied in a sealed condition prior to exposure. After exposure, the tubes were again sealed and returned to Gradko for analysis.

The UK Local Air Quality Management Technical Guidance LAQM.TG(22) ²⁶ states that when using diffusion tubes for indicative NO₂ monitoring, correction should be made where applicable for any systematic bias (i.e. over-read or under-read compared to the automatic chemiluminescent technique; the reference method for NO₂). A bias adjustment factor can be calculated due to the co-location of diffusion tubes with the automatic monitoring site at Beresford Street Market. This bias adjustment factor can be applied to the annual mean diffusion tube measurements in this survey. The NO₂ diffusion tube results in this report are uncorrected except where clearly specified. BTEX results have not been bias adjusted as BTEX diffusion tubes are not affected by the same sources of bias as NO₂ diffusion tubes.

Each monthly batch of diffusion tubes was accompanied by a ‘travel blank’ NO₂ and BTEX tube. The purpose of these tubes was to indicate if any contamination of the tubes had occurred. This was particularly relevant in the case of the BTEX tubes as they can easily be contaminated by exposure to solvents. These ‘travel blank’ tubes were taken with the exposure tubes to the site but were not exposed. They were returned to the site operator’s premises and were kept in a sealed bag in a cupboard. When the exposed tubes were collected, the ‘travel blank’ tubes were taken by the operator to the site. The travel blanks were sent with the exposed tubes for analysis.

Gradko also retained one tube from each batch, in a sealed bag in their premises, as a ‘laboratory blank’. The travel blank results for NO₂ were not used to apply any correction to the results from the exposed tubes – only to highlight possible contamination issues. BTEX results were blank corrected using the travel blank, or the laboratory blank where the analyst judged this to be appropriate.

2.3.2.4 Calendar of Diffusion Tube Exposure Periods

The calendar of exposure periods used for the NO₂ and BTEX diffusion tubes is shown in Table 1. They were intended to be an approximation to calendar months, while allowing for the tubes to be changed on a consistent day of the week. It was not always possible to stick to the intended dates, actual change over dates are also shown in the below Table 1.

2.4 Monitoring Sites

Automatic monitoring of oxides of nitrogen was carried out at the Central Market, Beresford Street, in St Helier shown in Figure 3 between 1^st January and 31^st December 2024. This site represents a roadside location where NO₂ concentrations are expected to be high and where members of the public are regularly exposed for periods of one hour or more. The inlet funnel (circled) is located on a column at a height of approximately four meters. The chemiluminescent NO_x analyser itself shown in Figure 4 is located within the building. The analyser is calibrated by the Government of Jersey’s Water and Air’s Technical officers. Details of the calibration procedure is provided in Appendix 2.

Figure 3: Beresford Street Market air quality monitoring site

Figure 4: Automatic NO_x analyser at Beresford Street Market, St Helier

Diffusion tubes were used to monitor NO₂ at sites in a range of different environments around Jersey, as described above.

Diffusion tubes were also co-located with the automatic monitoring site at Beresford Street Market, and the results of this co-located monitoring have been used to assess the precision and accuracy of the diffusion tubes, relative to the automatic chemiluminescent analyser, which is defined within Europe as the reference method for NO₂. The tubes at this site were exposed in triplicate, to allow assessment of precision. All other diffusion tube sites had single tubes deployed.

In July 2024, the diffusion tubes at St Luke’s Roadside and St Luke’s Playground monitoring locations were removed. These sites were used temporarily to assist in the monitoring of pollutant concentrations during the School Street Pilot Scheme that took place in 2023.

Automatic monitoring of particulate matter concentrations was carried out at three locations between 1^st January and 31^st December 2024, Central Market Osiris (JER09), Howard Davis Park Osiris (JER6) and Howard Davis Farm Osiris (JER10). The Central Market Osiris monitoring site is described as a roadside site and is located at the Central Market in St Helier, as shown in Figure 5. The long-running automatic monitoring site located in the Howard Davis Park Osiris is classified as an urban background site and is located near the centre of the park, 77 metres from the nearest road and 330 metres from the beach at Havre Des Pas (Figure 6). In June 2024, monitoring of particulate matter concentrations at Howard Davis Park ended and the Osiris monitor was moved to a new monitoring location at Howard Davis Farm which is classified as a rural site.

Figure 5: Central Market Osiris air quality monitoring site

Figure 6: Howard Davis Park Osiris air quality monitoring site

Figure 7: Howard Davis Farm Osiris air quality monitoring site

BTEX hydrocarbons were monitored at five sites during 2024 shown on Figure 8. The aim was to investigate sites likely to be affected by different emission sources and compare these with background sites.

Le Bas Centre is intended to monitor hydrocarbon concentrations at an urban background location. Rue de Pres Trading Estate, in an industrial estate near to a paint spraying business. The Faux Bie site is located near a fuel filling station, a potential source of hydrocarbon emissions including benzene. This monitoring site is intended to represent public exposure to emissions from the filling station as it is located between a fuel filling station and a nearby block of flats. The fuel supplier uses a vapour recovery system to reduce emissions when filling the storage tanks and has done so since December 2003. A Stage 2 Vapour Recovery System was later installed at the fuel filling station in 2016, and the replacement of the fuel storage tanks took place during August 2017.

The Harrington’s Garage site was introduced as a replacement to the Airport Fence location and has been in operation since January 2019. The site is located on the A13 Rue de Genets, aiming to assess levels of BTEX from a typical garage with petrol and diesel storage and dispensing facilities where there is no Vapour Recovery system currently in place. The BTEX tube is located on a down pipe attached to a domestic dwelling within the boundary of the petrol station.

Figure 8 shows a map of the locations of all monitoring sites used in this study. The map can be zoomed in and out and more information on the monitoring sites can be obtained from clicking on the marker. Note the following regarding site classifications:

• Kerbside: less than 1m from kerb of a busy road.
• Roadside: 1 - 5m from kerb of a busy road.
• Background: > 50m from the kerb of any major road.

3.1 Quality Assurance and Quality Control

A full intercalibration audit of the Beresford Street Market air quality monitoring site takes place annually, summarised in Table 3. The air intake sampling system is cleaned, and all other aspects of site infrastructure are checked in addition to standard checks of the instrument and calibration.

Following the instrument and calibration gas checking, and the subsequent scaling and ratification of the data, the overall accuracy and precision figures for the pollutants monitored at Jersey can be summarised as shown in Table 3. These are given in ppb, the “native” unit of the automatic data.

4.2 Diffusion Tube Uncertainty and Detection Limits

Diffusion tubes are an indicative technique, with greater uncertainty than more sophisticated automatic methods. The reported margins of uncertainty on the analysis are shown in Table 8. However, uncertainties arising from the exposure phase also contribute to the overall uncertainty; it is usually estimated that the overall uncertainty on diffusion tube measurements are approximately ± 25% for NO₂ and BTEX hydrocarbons.

The limits of detection in ambient air depend partly on the exposure time, and therefore vary to some extent from month to month. The analytical limit of detection was in the range 0.028 μg NO₂ to 0.031 μg NO₂. The ambient concentration that this equates to depends on the exposure period, but for the 4-week and 5-week periods used in this study, the limit of detection ranged from 0.491 μg m^-3 to 0.636 μg m^-3. The limit of detection for benzene equated to an ambient concentration between 0.21 μg m^-3 and 0.27 μg m^-3. The laboratory advises that there is a higher level of uncertainty for results lower than 10 times the limit of detection (LOD). For NO₂ diffusion tube monitoring sites, most ambient concentrations measured are well above this threshold, except for NO₂ measurements at Les Quennevais and Rue des Raisies. Therefore, the NO₂ concentrations at these two sites are likely to have overall uncertainty greater than ± 25% and should be treated as indicative only. However, for BTEX hydrocarbons in Jersey, this was not the case for most measurements except for benzene, toluene and mp xylenes at some sites and other isolated measurements. The BTEX hydrocarbon measurements are therefore likely to have overall uncertainty greater that ± 25% and should be treated as indicative only.

4.5 Comparison with Air Quality Guidelines, Limit Values and Objectives

Limit values, AQS objectives and WHO guidelines for all pollutants are described in earlier sections of this report. These are based on the 1-hour, 24-hour and annual means.

All Jersey sites had data capture less than 90%, therefore the annual means may not be representative of the entire year and direct comparison to limit values and objectives should be treated with caution. When data capture is between 75% and 85%, it is possible to express concentrations as percentile values to approximate the number of limit value exceedances. This only applies to Jersey Beresford Market since the data capture of the Osiris analysers was less than 75%.

Where automatic monitoring is completed for less than 75% of the year, annualisation techniques can be employed to estimate an annual average from a period average. This is done through extrapolation of monitoring results using data from nearby background sites.

The Beresford Street Market automatic analyser measured an annual mean NO₂ concentration of 15.1 μg m^-3. This would meet the annual mean limit value of 40 μg m^-3.

The updated WHO guidelines introduced in 2021 advise an annual mean limit for NO₂ of 10 μg m^-3. NO₂ concentrations measured at Beresford Street Market would not meet this guideline in 2024.

The 99.8^th percentile of 1-hour NO₂ at the Beresford Street Market automatic monitoring site was 72.8 μg m^-3. This shows that, had the data capture been 100%, it is likely that there would have been less than 18 exceedances of 200 μg m^-3 in 2024. Therefore, this site would likely meet the AQS objective for this parameter.

The period mean PM₁₀ concentration measured at Central Market Osiris was 20.7 μg m^-3. Due to the low data capture at Central Market Osiris, data was annualised to give an accurate estimate of the annual mean measured at the site. Following this process the annual mean was calculated to be 20.1 μg m^-3.At Howard Davis Park Osiris and Howard Davis Farm Osiris the period mean concentrations were 12.5 μg m^-3 and 9.6 μg m^-3 respectively. Following the annualisation process, the annual means measured at Howard Davis Park Osiris and Howard Davis Farm Osiris were 12.0 μg m^-3 and 9.5 μg m^-3 respectively. These annual means would meet the annual limit value of 40 μg m^-3 for PM₁₀ concentrations. Annual mean PM₁₀ concentrations measured at Howard Davis Park and Howard Davis Farm would also meet the annual mean WHO guideline of 15 μg m^-3 for PM₁₀. However, the annual mean PM₁₀ concentration measured at Central Market Osiris would not meet the annual mean WHO guideline for PM₁₀ concentrations.

The 24-hour mean of 50 μg m^-3 for PM₁₀ concentrations was exceeded on 4 occasions at Central Market Osiris and on 1 occasion at Howard Davis Park Osiris during the monitoring period. Both sites are therefore shown to be below the allowed 35 exceedances. However, both Osiris monitors had low data capture and therefore the number of exceedances may have been greater if data capture been higher.

The period mean PM_2.5 concentration measured at Central Market Osiris was 7.7 μg m^-3 and the annual mean measured at Howard Davis Park Osiris and Howard Davis Farm Osiris was 7.0 μg m^-3 and 5.1 μg m^-3, respectively. Due to the low data capture at these sites, annualisation was carried out to estimate the annual mean at each monitoring site. Following the annualisation process, the annual mean PM_2.5 concentration measured at Central Market Osiris was 7.3 μg m^-3. The estimated annual means measured at Howard Davis Park Osiris and Howard Davis Farm Osiris sites were 6.7 μg m^-3 and 5.3 μg m^-3 respectively. These annual means would meet the annual limit value of 20 μg m^-3 for PM_2.5 concentrations. However, PM_2.5 concentrations measured at the three Osiris monitoring locations would not meet the annual mean WHO guideline of 5 μg m^-3 for PM_2.5.

Due to the long sampling period of diffusion tubes, it is only possible to compare the results from the diffusion tube sites in this study against limit values relating to the annual mean. The raw and bias adjusted annual average recorded at all diffusion tube monitoring locations in 2024 are within the AQS objective of 40 μg m^-3.

The recorded bias adjusted annual means of twelve diffusion tube monitoring locations are lower than the 2021 WHO annual mean guideline for NO₂ of 10 μg m^-3.

The 30 μg m^-3 limit for protection of vegetation is only applicable at rural sites and is therefore only relevant to Rue des Raisies. The annual mean NO₂ concentration of 2.51 μg m^-3 at this rural site was well within the limit value.

4.9 Back Trajectory Analysis

Back trajectory plots show data from the HYSPLIT model ²⁹ run in analysis mode. These show the air mass back trajectories for the period covered by the report. Two different types of plots are shown. One statistically groups the trajectories into similar clusters and shows the proportion of time during the report period that each represents Figure 31. This is useful to get an overview of air mass origins during the report period. Multiple plots of the back trajectories associated with the top 10 most polluted days for each pollutant are also presented in Figure 32 to Figure 33.

4.9.1 Trajectory Clusters

72-hour air mass back trajectories arriving at Jersey for the reporting period are grouped into 4 clusters, shown in Figure 31. This shows the approximate proportion of time air masses were arriving from each compass point during 2024.

Air mass back trajectories over these spatial scales do not vary locally so the receptor location used in this report has been selected from a range of national receptor locations maintained by Ricardo. The receptor point used here is Jersey.

Figure 31: 72-hour air mass back trajectories arriving at Jersey during 2024

4.11 Trends in NO₂ at Long-running Sites

The annual mean NO₂ concentrations for diffusion tube sites which had over 75% data capture are illustrated in Figure 39. The data is not adjusted for diffusion tube bias as there was no reliable information on which to carry out bias adjustment prior to 2002. Therefore, for consistency, unadjusted data is used in this section.

Broad Street became pedestrianised on the 23^rd of May 2020 in order to allow greater social distancing for pedestrians, this is reflected in a 27% reduction in the annual mean concentrations in 2020. This was followed by subsequent decreases in 2021 and 2022 to 17 μg m^-3 and 16 μg m^-3 respectively. In 2024, the annual concentration has further decreased to 14 μg m^-3.

From 2004 onwards, annual mean NO₂ concentrations at historic kerbside, roadside and urban background sites (Weighbridge, Georgetown, Beaumont, The Parade, Broad Street, and Le Bas Centre) show an overall decreasing trend. In 2023, NO₂ concentrations were shown to decrease at most sites. Three sites showed minimal change in concentrations (Rue Des Raisies, Overdale Entrance and Overdale Nursery) and no sites showed an increase in concentrations between 2023 and 2024. Furthermore, all sites remained below 40 μg m^-3.

Table 15 illustrates annual mean NO₂ concentrations at several of the sites have remained stable with typical fluctuations from year to year due to meteorological conditions and other factors since 2012.

As traffic volumes have increased since monitoring began, fluctuations in concentrations are likely linked to increased vehicle efficiency and cleaner fuels. A recent study into vehicle emissions in Jersey ³⁰ found that newer petrol vehicles produce fewer NO_x emissions. It also found that there has been an overall decline in diesel vehicles on the island and an increase in newer petrol cars.

A focused example of the differences between closely located site locations indicates how localised NO₂ distribution can be with certain mitigating factors. A comparison between the now discontinued New Street site and Union Street shows New Street generally measured lower concentrations than Union Street. These sites were very close with the Union Street tube located on the corner of Union Street and New Street which run perpendicular to each other. New Street is access only and therefore, carries much lower traffic volumes. Furthermore, very little pollution from Union Street is carried to New Street, located to the South, as the prevailing wind is from the West with the least wind coming from the North.

4.12 Hydrocarbons

Full monthly results of the hydrocarbon survey for the five BTEX sites and a summary of the annual average hydrocarbon concentrations are shown below. Travel blank values gave consistently lower results than the exposed tubes with the exception of most pollutants in January 2024 which had elevated levels in the Travel Blank. The following exposure was noted to have a loose end cap and it is therefore possible that the elevated concentrations reported were influenced by this:

• November 2024 - Harrington’s Garage

The deployment listed above corresponds with elevated concentrations measured by the BTEX tubes, therefore these measurements should be treated with caution. These results are considered outliers, likely due to loose end caps following exposure and have therefore been rejected.

Table 17 lists the missing BTEX tube results throughout 2024, including outliers and missing tube results.

5.1 NO₂ Results

1. The period mean NO₂ concentration measured by the automatic analyser at Beresford Street Market was 15 μg m^-3 (rounded to the nearest integer). This is therefore within the AQS objective of 40 μg m^-3 for annual mean NO₂. Having achieved compliance by 2010 as required by all European Union member states the Government of Jersey are advised to continue to demonstrate ongoing compliance as has been done since 2010. This site recorded 84.4% data capture for the 2024 calendar year.
2. The AQS objective for 1-hour mean NO₂ concentration is 200 μg m^-3, with 18 exceedances permitted per calendar year. The highest hourly value measured was 309.9 μg m^-3. As the data capture for this site was between 75% and 85%, the concentrations can be expressed as a percentile value to estimate the number of exceedances of this limit value. The 99.8^th percentile of 1-hour NO₂ at the Beresford Street Market automatic monitoring site was 72.8 μg m^-3. Therefore had the data capture been 100%, it is likely that there would have been less than 18 exceedances of 200 μg m^-3, and therefore the limit value would likely be met in 2024.
3. NO₂ diffusion tubes exposed in triplicate alongside the automatic analyser at Beresford Street Market measured a bias adjusted annual mean of 13 μg m^-3.
4. Annual mean NO₂ concentrations at all diffusion tube monitoring sites were within the EC limit value of 40 μg m^-3.
5. The updated WHO guidelines introduced in 2021 advise an annual mean limit for NO₂ of 10 μg m^-3. Beresford Street Market would not meet this guideline during 2024.
6. Twelve diffusion tube monitoring locations measured annual mean NO₂ concentrations lower than the 2021 WHO annual mean NO₂ guideline of 10 μg m^-3
7. NO₂ concentrations at Beresford Street Market were shown to be lower in 2024 compared to 2023. 2024 is the third full calendar year of monitoring at Beresford Street Market, therefore it is difficult to make direct comparisons between this site and others. Jersey is also continuing its recovery from the COVID-19 Pandemic, therefore making comparisons between previous years difficult. It is recommended that monitoring is continued at Beresford Street Market for further years to enable these comparisons.
8. Seasonal variations in monthly mean NO₂ concentrations at the diffusion tube sites are generally shown to be highest in January, February and October whilst lower concentrations were seen between June and August.
9. The diurnal variation in NO₂ concentrations at Beresford Street Market showed a similar pattern to an urban site. The expected morning peak is particularly early and sharp, followed by a broad evening peak at rush hour. This is likely a result of traffic patterns around the site, particularly traffic associated with market operations, such as market traders and delivery vehicles.
10. Annual mean NO₂ concentrations at Jersey’s urban sites have shown a general decreasing trend between 2012 and 2023. Since then, concentrations have been shown to remain largely stable at the majority of sites.
11. Annual mean NO₂ concentrations at all of Jersey’s diffusion tube monitoring sites showed a decrease in concentrations in 2024 compared to 2023. Pollutant concentrations are expected to fluctuate from year to year, due to meteorological and other factors, the COVID-19 pandemic being the obvious major one for 2020 and beyond.

5.2 PM₁₀ and PM_2.5 Results

1. Central Market Osiris recorded a data capture of 68.5% in 2024. Furthermore, Howard Davis Park Osiris and Howard Davis Farm Osiris also recorded low data captures of 47.4% and 49.6% respectively. This is below the recommended 90% data capture required to report an annual mean and compare to limit values and objectives. Where automatic monitoring is completed for less than 75% of the year, annualisation can be applied to estimate an annual average to allow comparison again limit values and objectives.
2. The annualised annual mean PM₁₀ concentration measured at Central Market Osiris was 20 μg m^-3 (rounded to the nearest integer). Howard Davis Park Osiris and Howard Davis Farm Osiris measured annualised annual means of 12 μg m^-3 and 10 μg m^-3 respectively. These annual means would meet the annual limit value of 40 μg m^-3 for PM₁₀ concentrations. Annual mean PM₁₀ concentrations measured at Howard Davis Park and Howard Davis Farm would also meet the annual mean WHO guideline of 15 μg m^-3 for PM₁₀. However, the annual mean PM₁₀ concentration measured at Central Market Osiris would not meet the annual mean PM₁₀ WHO guideline.
3. The annualised annual mean PM_2.5 concentration measured at Central Market Osiris was 8 μg m^-3 (rounded to the nearest integer). Howard Davis Park Osiris and Howard Davis Farm Osiris measured annualised annual means of 7 μg m^-3 and 5 μg m^-3 respectively. These annual means would meet the annual limit value of 20 μg m^-3 for PM_2.5 concentrations. However, PM_2.5 concentrations measured at the three Osiris monitoring locations would not meet the annual mean WHO guideline of 5 μg m^-3 for PM_2.5.
4. The diurnal variation in PM₁₀ and PM_2.5 concentrations at Central Market Osiris show a broad morning peak followed by a smaller peak in the evening. This pattern is likely attributed to traffic patterns around the site, particularly those associated with market operations as well as general public use.
5. The diurnal variation in PM₁₀ and PM_2.5 concentrations at Howard Davis Park Osiris shows concentrations are lower at this site compared to Central Market Osiris, likely due to the location of the site in the centre of the park. There is shown to be a broad morning peak followed by a smaller peak in the evening to which rush hour traffic is a contributing factor.
6. The diurnal variation in PM₁₀ and PM_2.5 concentrations at Howard Davis Farm Osiris shows a similar pattern to those shown at Central Market Osiris and Howard Davis Farm Osiris, although to a lower magnitude. PM₁₀ and PM_2.5 concentrations are also shown to be elevated overnight.
7. Investigation of particulate matter concentrations with wind speed and wind direction show that elevated concentrations of PM₁₀ and PM_2.5 primarily occurred under unsettled conditions. At Central Market Osiris and Howard Davis Park Osiris, this was primarily under high wind speeds from the southwest, in the direction of the port and marinas. At Howard Davis Farm Osiris, elevated concentrations were shown predominantly under high wind speeds from the northwest.
8. Back trajectories from the top ten most polluted days for PM₁₀ and PM_2.5 at Central Market Osiris and Howard Davis Park Osiris indicate that elevated concentrations were predominantly associated with wind directions from the west. This shows that elevated concentrations are not likely associated with long range transport of polluted air masses from the continent. Conversely, the back trajectories for Howard Davis Farm Osiris indicate that particulate matter concentrations may be influenced by local sources such as agricultural land and an animal carcass incinerator as well as long range transport of pollution from the continent as some air masses are shown to originate from mainland Europe and north Africa.

5.3 Hydrocarbon Diffusion Tube Results

1. Annual mean benzene concentrations at all five sites were within the EC Directive limit value of 5 μg m^-3. Having achieved compliance by 2010 as required, the Government of Jersey must continue to demonstrate ongoing compliance.
2. All sites measured relatively low annual mean concentrations of each pollutant. However, Harrington’s Garage showed slightly higher average measurements than the other four sites for toluene, ethylbenzene, m+p-xylene and o-xylene, possibly as a result of the proximity of this site to fuel filling stations. Harrington’s Garage also recorded the highest average concentrations for benzene concentrations.
3. Annual mean concentrations of benzene were shown to be similar or lower than those measured in 2023 at all sites expect Beresford Street, where concentrations were shown to decrease slightly. Toluene concentrations at three monitoring sites were similar or lower than those measured in 2022, however toluene concentrations at Harrington’s Garage and Rue de Pres both showed small increases compared to 2023.
4. Annual mean concentrations of ethylbenzene, m+p-xylene and o-xylene were shown to decrease or remain the same at all BTEX monitoring sites in 2024 when compared to those measured in 2023, except for those measured Harrington’s Garage which showed a small increase in 2024.

5.4 Recommendations

It is recommended that the monitoring programme be continued as part of Jersey’s Air Quality Strategy and that quality assurance and quality control (QAQC) practices are continued for all analysers including the Osiris monitors located at Central Market and Howard Davis Park. The Osiris monitors may be replaced with low-cost sensor units in the future and therefore it is recommended that best practice QA/QC procedures for sensors should be followed. Furthermore, a new reference site is planned to be installed in Jersey, this site will include a reference PM analyser that will also enable the co-location of sensors that form Jersey’s sensor network.

Measured concentrations of BTEX hydrocarbons at most of the sites were very low. The results should therefore only be taken as indicative measurements, for the purpose of confirming that benzene concentrations at the sites are within relevant limit values. However, if accurate measurement of hydrocarbons are required, it may be appropriate to consider installation of pumped-tube sampling at key sites, as used at UK mainland Non-Automatic Hydrocarbon Network sites. As BTEX concentrations at the current monitoring sites have remained low for numerous years, a review of the current VOC network is recommended to identify any sites which may be suitable for relocation to new monitoring locations. Locating a BTEX tube close to the La Collette Terminal is recommended to monitor BTEX concentrations that may be associated with the fuel farm. To further reduce VOC emissions from petrol stations and Jersey’s fuel farm it is recommended that the States of Jersey consider developing vapour recovery legislation.

Continual review of the diffusion tube network is recommended to assess any sites that no longer represent relevant exposure and can be removed or relocated. The results outlined in this report indicate that no sites have breached the annual average NO₂ limit values. As such, an expansion of the automatic NO_x monitoring network is not required, although it is recommended that monitoring continues at the Beresford Street Market urban roadside location. Monitoring at Beresford Street allows better comparison between the other roadside and kerbside diffusion tube sites and enables an appropriate co-location for diffusion tubes used for annual BIAS adjustment. It also ensures that Jersey’s monitoring network aligns with the strategy stated in LAQM.TG(22) whereby monitoring sites are “sufficiently close to the dominant pollution source (i.e. in the vast majority of cases, at roadside sites)”³³. If the Government of Jersey would like to expand the network, monitoring at a background site would be beneficial to “determine long-term trends, as such sites are less likely to be affected by variations in local sources, for example, changes in traffic on a particular road” ³⁴.

Continuation of quality assurance and quality control (QAQC) practices for measured data from the Osiris monitors is recommended.

Based on the 2019 UK Clean Air Strategy ³⁵ and its emphasis on PM_2.5 reduction the Government of Jersey may wish to install reference equivalent analysers in an aim to expanding their particulate monitoring network and demonstrating compliance with the annual WHO PM_2.5 guideline of 5 μg m^-3.

With ongoing reductions in concentrations and improvements in technology since the Jersey Air Quality Strategy was last published in 2013, now would be a good opportunity to review and potentially update the document.

Ricardo understands that with a recent restructure during 2021, with Air Quality monitoring moving to a dedicated scientific team, and Government Plan funding allocation, the Government of Jersey have moved to prioritise the development of the existing Air Quality monitoring programme to meet new and existing environmental challenges.