| Pollutant | Type | Year in force | Metric | Value |
|---|---|---|---|---|
NO2 |
LV |
2010 |
Annual mean |
40 μg m-3 |
NO2 |
LV |
2010 |
1-hr mean |
200 μg m-3 (18 allowed) |
PM10 |
LV |
2005 |
Annual mean |
40 μg m-3 |
PM10 |
LV |
2005 |
24-hr mean |
50 μg m-3 (35 allowed) |
PM2.5 |
TV/LV (Stage 1) |
2010/2014 |
Annual mean |
25 μg m-3 |
PM2.5 |
LV (Stage 2) |
2020 |
Annual mean |
20 μg m-3 |
CO |
LV |
2005 |
Maximum daily running 8-hr mean |
10 mg m-3 |
SO2 |
LV |
2005 |
1-hr mean |
350 μg m-3 (24 allowed) |
SO2 |
LV |
2005 |
24-hr mean |
125 μg m-3 (3 allowed) |
O3 |
LTO |
Not defined |
Maximum daily running 8-hr mean |
120 μg m-3 |
Benzene |
LV |
2010 |
Annual mean |
5 μg m-3 |
Lead |
LV |
2005 |
Annual mean |
0.5 μg m-3 |
B[a]P |
TV |
2013 |
Annual mean |
1 ng m-3 |
Arsenic |
TV |
2013 |
Annual mean |
6 ng m-3 |
Cadmium |
TV |
2013 |
Annual mean |
5 ng m-3 |
Nickel |
TV |
2013 |
Annual mean |
20 ng m-3 |
Air Quality in Gibraltar
2022 Air Quality Data Digest
1 Introduction
1.1 Air quality monitoring in Gibraltar
The Gibraltar Air Quality Data Digest provides an annual summary of the air pollutant measurements from the Gibraltar Air Quality Monitoring Network for 2022.
The Gibraltar Air Quality Monitoring Network is operated on behalf of the Government of Gibraltar by the Environmental Agency, with assistance from Ricardo Energy & Environment. The Gibraltar Air Quality Monitoring Network was established for compliance against the European Air Quality Directive (AQD) on ambient air quality and cleaner air for Europe (2008/50/EC) and the Fourth Daughter Directive (DD4) (2004/107/EC) and continues to provide the highest quality evidence of ambient pollution concentrations across Gibraltar. At the instruction of HM Government of Gibraltar, the analysis presented in this summary report is compared against the Limit Values, Target Values and Long Term Objectives laid out in the AQD to ensure valid comparison against established metrics and thresholds. The Gibraltar Air Quality Monitoring network continues operation in line with best practice and criteria established under the AQD and DD4. The data quality and coverage therefore remains comparable with the rest of Europe.
The Gibraltar Air Quality Monitoring Network includes a mixture of automatic pollutant monitoring stations and non-automatic air pollutant monitoring sites. The automatic air quality monitoring stations measure:
Oxides of nitrogen (NOX) and nitrogen dioxide (NO2)
Sulphur dioxide (SO2)
Ozone (O3)
Carbon monoxide (CO)
Particulates (PM10, PM2.5)
Heavy metals: Arsenic (As), Cadmium (Cd), Nickel (Ni), Lead (Pb)
Benzene (Bz) and
Polycyclic aromatic hydrocarbons (PAH), including Benzo[a]Pyrene (B[a]P).
Non-automatic sites measure monthly average concentrations of NO2 and benzene using a passive diffusion tube based method. Diffusion tube measurements have a much higher uncertainty than automatic measurements and are purely indicative of air pollutant concentrations. As such they cannot be compared against the specific legislative values specified in the European Air Quality Directive. Further information on the air pollutants measured in Gibraltar can be found on the Air Quality in Gibraltar website.
The sites within the Gibraltar automatic air quality monitoring network provide a combination of high resolution hourly measurements and daily average air pollutant concentrations. High resolution information is communicated rapidly to the public. The main platform for information dissemination of air quality measurement in Gibraltar is the Air Quality in Gibraltar website. Non-automatic measurement sites provide an indicative measure of roadside and background air pollutant concentrations at thirty-two sites throughout Gibraltar.
The major objectives of the Gibraltar Air Quality Monitoring Network are:
Checking if statutory air quality standards and targets are met (e.g., EC Directives)
Informing the public about air quality
Identifying long-term trends in air pollution concentrations
Assessing the effectiveness of policies to control pollution in Gibraltar, as laid out in the Gibraltar Air Quality Action Plan.
The air pollutant measurements from Gibraltar Air Quality Monitoring Network are used for:
Reporting to the European Commission as required by the Air Quality Directives
Comparison with air quality objectives prescribed by the Air Quality Directives
Providing the public with information through air quality bulletins
Forecasting future air quality levels
Policy development for human health protection.
This document provides graphical analysis and explanatory summaries of the air pollutant measurements made in Gibraltar. Compliance plots (as discussed in Section 2.2) are used to present concentrations for 2022 in the context of historical data, highlighting whether the Limit Values (LVs) or Target Values (TVs) given in the European Air Quality Directives were achieved. The other plots presented here provide useful information from which the source of air pollutants can be inferred.
1.2 Limit Values and Target Values
A summary of the relevant legislative thresholds prescribed in the Air Quality Directive and Fourth Daughter Directive are presented in Table 1. This shows each pollutant and the relevant metric and threshold applicable. Also shown is the type of threshold: Limit Value (LV), Target Value (TV), Long Term Objective (ozone only) and the year in which each LV or TV has to be achieved. These are represented in the ‘compliance plots’ as red dashed lines and the corresponding metrics are also presented in the summary data tables in this document. The air pollutants covered under the two Directives are:
Air Quality Directive (AQD)
NOX and NO2
PM10
PM2.5
CO
SO2
Ozone
Benzene
Lead
- Fourth Daughter Directive (DD4)
Benzo[a]Pyrene (B[a]P)
Arsenic
Cadmium
Nickel
1.3 Air quality monitoring locations
Information on the air pollutant monitoring methods and the composition of the Gibraltar Air Quality Monitoring Network can be found on the Gibraltar Air Quality Monitoring Network website. Table 2 provides a summary of the air pollutant monitoring stations and air pollutants measured at the automatic monitoring stations and non-automatic monitoring sites in Gibraltar in 2022. Figure 1 and Figure 2 show the locations of the automatic monitoring stations and the non-automatic sampling points in Gibraltar in 2022, respectively. Mobile monitoring has been added into the network since 2018 and these sites and concentrations have been presented in Section 3.8.
| Station name | Pollutants measured |
|---|---|
| Automatic monitoring sites | |
Bleak House |
NOX, NO2, PM10 and ozone |
Rosia Road |
NOX, NO2, PM10, PM2.5, CO, SO2, benzene, PAH and metals |
Withams Road |
NOX and NO2 |
| Non-automatic monitoring sites | |
Multiple sites |
NO2 and/or benzene |
1.4 Data processing
The data summaries and plots presented in this document were generated based upon functions originally from the openair package, an open-source air quality analysis toolset written in the R statistical programming language.
1.5 Meteorological observations
A summary of 2022 meteorological observations are presented to provide a context for the air pollutant concentrations measured in Gibraltar. The influence of the Rock on the flow of the wind field is evident: wind speed and direction measurements vary markedly when correponding measurements are compared to one another. Wind speeds measured using the Gibraltar Airport meteorological mast (reference height, z = 10 m), tend to be higher than those measured at the three automatic air quality monitoring stations, where wind speeds are measured at a height of 6-8 m, and are therefore correspondingly lower. Meteorological data from Gibraltar Airport has been included for comparison with the local meteorological data from the AQ monitoring stations and is considered to be more representative of the regional meteorological conditions. Plots that use meteorological data have been generated using the local meteorological data where it is available (e.g. fixed automatic stations), which are associated with the corresponding concentrations resulting from the local dispersion conditions. However, it is important to be mindful that the regional meteorological conditions can be quite different. Where meteorological data is not available to associate directly with concentrations, the regional meteorological data from the airport has been used instead (e.g. AQMesh pods).
2 Description of plot types
This section provides a summary of the main plot types used in the Gibraltar Air Quality Data Digest. The caption of each plot is cross-referenced to this section to allow the reader to easily find the summary description of the plot.
2.1 Interactive map
Interactive maps use markers to show points of interest, for example measurement sites. The user can zoom in and out to see more or less detail. The user can also turn satellite layers on and off by selecting a different base map, using the top right button.
2.2 Compliance plot
The compliance plots show the mean concentrations, expressed as annual mean or an appropriate equivalent percentile for the year. This allows comparison of the mean value with a legislative threshold, e.g. an air quality Directive Limit Value (LV) or Target Value (TV) which is represented by the dashed black line. In instances where the European air quality Directives specify a permissible number of occasions above a threshold, the plotted data are presented as the percentile equivalent to that metric. For example, 99.8th percentile of hourly mean NO2 concentrations is equivalent to 18 permissible exceedances of the hourly NO2 LV (200 μg m-3). Compliance is indicated by values below 200 μg m-3. Likewise for PM10, the 90th percentile of daily mean PM10 is equivalent to 35 permissible exceedances of the daily PM10 LV (50 μg m-3). PM2.5 has two thresholds specified by the Directive: A Stage 1 LV and TV at 25 μg m-3 and a Stage 2 LV at 20 μg m-3.
The user can zoom in and out to different time periods to see more or less detail by using the mouse to click and drag on the time series. The user can also mouse over a data point to get more information. Clicking on the legend can add or remove different traces.
2.3 Wind rose
The wind rose plot shows the variation in wind speed and direction at a site. The classified colour scale represents different wind speeds (in m s-1). The magnitude of the wind speed is shown by the colours indicated in the colour bar. The orientation of the wind sectors around the plot origin represents the wind direction binned in 30° sectors. The distance outwards from the plot origin represents percentage of time the wind speed originated from a particular direction. Therefore by adding each percentage together should sum to 100.
2.4 Trend plot
The trend plot shows monthly mean air pollutant concentrations (indicated by a thin line joining closed circles) and the non-linear trend fitted to the data (bold line). The shaded bands represent the 95% confidence interval of the data. These plots demonstrate temporal trends over months and/or years and can be used to determine long-term trends.
The user can zoom in and out to different time periods to see more or less detail by using the mouse to click and drag on the time series. The user can also mouse over a data point to get more information. Clicking on the legend can add or remove different traces. The smoothed trend and the monthly values can be removed separately.
2.5 Contribution plot
Contribution plots show the influence of the wind direction on mean air pollutant concentrations. As with the wind rose, the orientation of the wind sectors around the plot origin represents the wind direction binned in 30° sectors. The radial scale indicates the percentage of time the wind from a particular wind sector contributed to the overall mean concentration. The plots show the contribution of each wind sector to the overall mean air pollutant concentration; this is particularly useful for showing the influence of wind direction on high air pollutant concentrations.
2.6 Calendar plot
Calendar plots are laid out in a similar style to a wall calendar and show the daily mean air pollutant concentrations disaggregated by day-of-week and month-of-year. The colour of each box corresponds to the daily mean pollutant concentration indicated by the colour bar. The prevailing daily wind direction is indicated by the orientation of the arrow in each box. This allows the daily mean air pollutant concentrations to be seen relative to one another. It also allows seasonal patterns in air pollutant concentrations, trends, and the variation of the local wind field, as well as the influence of meteorology on air pollutant concentrations to be seen.
The user can hover over each “day” in the calendar to read the date, day of the week, pollutant concentration, and wind speed.
2.7 Polar plot
Polar plots show the relationship between air pollutant concentrations and wind speed and wind direction. The wind speed is represented by the distance from the plot origin and the wind direction is the orientation about the origin (as in other plots described above). The continuous colour scale represents the air pollutant concentration. The plot provides a continuous surface by smoothing between observed data points. Where meteorological data are not available at point of measurement (e.g. AQMesh pods), data from the airport meteorological station have been used.
2.8 Polar plot map
Where appropriate, polar plots can be visualised on an interactive map (similar to those described in Section 2.1). This can help triangulate sources and more easily compare polar plots of different sites and pollutants. The user can switch between pollutants using the control menu at the top-right of the plot.
When reading a polar plot map, users should note that each marker has its own colour scale. In other words, a dark red colour on one polar plot marker doesn’t correspond to the same concentration as the dark red on another.
2.9 Time variation plot
The time variation plot shows changing concentrations over several different time scales:
Hour of the day and day of the week (upper pane)
Hour of the day (diurnal variation, in the lower left pane)
Month (seasonal variation, in the lower central pane)
Day of week (in the lower right pane).
The time variation plot is useful for representing changes due to different source activities. For example, fugitive dust emissions from building work, which may cause an increase in the PM10 mass concentration, might occur at specific hours of the day or days of the week; likewise NOX and NO2 associated with road traffic exhausts are typically higher during week days than weekend and at morning and evening rush hours.
This plot requires high-resolution (hourly) measurements of air pollutant concentrations in order to produce the temporal plot shown across the top panel and on the bottom right hand-side of the plot. PM10 in Gibraltar is measured using two techniques: The FDMS, which provides hourly mean PM10 mass concentrations, and by the Partisol, which provides daily mean PM10 mass concentrations. PM2.5 is only measured using the Partisol method. Therefore it is not possible to produce a time variation plot for PM2.5 mass concentrations in Gibraltar.
The user can zoom in and out to different time periods to see more or less detail by using the mouse to click and drag on the time series. The user can also mouse over a data point to get more information. Clicking on the legend can add or remove different traces, which will change all four different panels of the time variation plot.
2.10 Spot concentration plot
The spot concentration plot shows the measured air pollutant concentration for a range of locations. This plot is ideal for summarising the results from the NO2 and benzene diffusion tube measurements from the Gibraltar non-automatic monitoring network. Air pollutant concentrations from the non-automatic monitoring network are measured at multiple sites
Two plots are presented for both pollutants. The first showing the annual mean air pollutant concentration at each site. The second shows the difference in the annual mean for the current year versus the long-term average, for each site, to show the long trends in air pollutant concentrations. This can be used to indicate whether air quality is improving or declining at these locations.
It should be noted that diffusion tube measurements are purely indicative of air pollutant concentrations. As such they cannot be compared against the specific legislative values specified in the European Air Quality Directive.
2.11 Interactive time series plot
Interactive time series plots show the measured air pollutant concentrations at an individual site or multiple sites. The user can zoom in and out to different time periods to see more or less detail by using the mouse to click and drag on the time series or by using the range slider bar at the bottom of the plot. The user can mouse over a pollutant trace to get more information on a specific data point. Pollutant traces can be turned on and off by clicking on the pollutant name in the legend. To see an individual pollutant channel at optimum scale, double click on the pollutant name to isolate one channel.
3 Meteorology
4 Compliance monitoring
4.1 NOX and NO2
4.2 Particulate matter
Gravimetric vs. Real-Time Particulate
Before 2021, particulate statistics in Gibraltar were calculated using data from particulate gravimetry. After 2021, continuous measurements were made using a FIDAS analyser. In long-term trend plots (e.g., Figure 16), gravimetric particulate is represented using a solid circle and continuously measured particulate with an empty circle.
4.3 SO2
4.4 CO
4.5 Ozone
4.6 Benzene
4.7 Directional Analysis Map
Figure 40 overlays polar plots on an interactive map of Gibraltar.
5 Mobile monitoring (AQMesh)
5.1 AQMesh Monitoring in 2022
In 2018 several AQMesh pods were added to the Gibraltar automatic monitoring network. The AQMesh uses electrochemical sensors to measure gaseous pollutants and a light scattering methodology to measure particulate matter. The measurements are described as indicative because direct calibration with reference materials is not possible for the detection techniques used. The pods have periodically been co-located with the reference instruments at Rosia Road in order to characterise the outputs and provide the best estimate of reported concentrations. These new monitoring technologies have been used to investigate potential pollution issues and in doing so have added to the overall understanding of air quality in Gibraltar.
The below table provides a summary of the AQMesh pods and Figure 41 shows the locations of the AQMesh pods in Gibraltar in 2022.
| Site name | Measurement period | Polluants measured |
|---|---|---|
Harbour Views Rd |
01/01/22 to 31/12/22 |
NO, NO2, NOX, PM10, PM2.5 and CO |
Devil’s Tower Road |
01/01/22 to 31/12/22 |
NO, NO2, NOX, PM10, PM2.5 and CO |
Rosia Road Clocktower |
01/01/22 to 31/12/22 |
NO, NO2, NOX, PM10, PM2.5 and CO |
Governor’s Lane |
08/09/22 to 31/12/22 |
NO, NO2, NOX, PM10, PM2.5 and CO |
5.2 Trend Analysis
AQMesh Carbon Monoxide
CO is measured in mg m–3 and as such is plotted separately to the other pollutants. CO concentrations measured at each AQMesh site are shown on the same plot.
5.3 Directional Analysis
NOx
Particulate Matter
Interactive Map
Figure 54 overlays polar plots on an interactive map of Gibraltar.
6 Summary Statistics
6.1 Compliance reporting sites
Data Capture
Caution is recommended when considering records with low data capture as these may not be representative of the full averaging period represented by the metric (e.g. annual mean concentrations).
PM Measurement Techniques
Before 2021, particulate statistics in Gibraltar were calculated using data from particulate gravimetry. After 2021, continuous measurements were made using a FIDAS analyser.
PM Measurement Techniques
Before 2021, particulate statistics in Gibraltar were calculated using data from particulate gravimetry. After 2021, continuous measurements were made using a FIDAS analyser.
AOT 40
AOT 40 is the sum of the differences between hourly concentrations greater than 80 μg m-3, i.e. 40 ppb, and 80 μg m-3, over a given period (the months of May-July) using only the 1-hr averages measured between 08:00 and 20:00 hrs.
6.2 AQMesh indicative sites
Data Capture
Caution is recommended when considering records with low data capture as these may not be representative of the full averaging period represented by the metric (e.g. mean concentrations).