Authors Ben Fowler
Compilation date 18 April 2024
Customer Spelthorne Borough Council
Approved by Louisa Kramer
Copyright Ricardo Energy & Environment
EULA http://ee.ricardo.com/cms/eula/

Contract reference ED15866 Report reference ED15866101

1 Introduction

This is an annual summary report for Spelthorne Borough Council covering the period 01/01/2023 - 31/12/2023.

This is a dynamic report which contains the data it displays embedded within and allows the reader a level of interaction with some of the findings. This enables a more easily navigated and streamlined report with a more engaging, intuitive reader experience.

Maps, tables and some plots have an element of interactivity to them which makes them easier to read or offers additional insight. Maps for example can be panned and zoomed with different layers and markers turned on and off and with popup information by clicking on markers or hovering the mouse over them. Tables may contain much more information than initially displayed and can be set to show different numbers of rows, and can be filtered sorted or searched to display only specific information of interest. Some time series plots can be tracked with the mouse cursor to obtain specific time/date stamps and values and the reader can zoom into a specific time window by dragging with the cursor and double left clicking to return to the full plot extent.

The report is easily navigable using the floating table of contents on the left pane which tracks with the reader’s progress through the report and expands and collapses to a level of detail related to the subheadings used. The layout of the report is also dynamic, with some sections split into specific ‘tabs’ (e.g. per pollutant or per site) for ease of access to those sections.

2 Monitoring stations

A summary of site information is presented in the interactive map and table below .

Figure 1: Location of sensor monitoring sites in Spelthorne

3 Air Pollutants

Nitrogen Dioxide (NO2)

NO2 is a gas that is mainly formed from combustion processes such as wood burning wood and vehicle emissions. When breathed in NO2 can irritant the throat and lungs and worsen symptoms in those with underlying respiratory issues. NO2 is also involved in the formation of photochemical smog and acid rain and may cause damage to crops and vegetation.

Particulate Matter (PM)

Particulate matter in the atmosphere has many man-made and natural sources, and can vary widely in its physical and chemical composition, and size. For air quality PM is typically classified into two sizes - PM10 is the concentration of particles with an effective median diameter of 10 micrometers (μm) and PM2.5 the concentration of particles with an effective median diameter of 2.5 μm. PM2.5 is sometimes known as “fine” particulate matter. Fine particulate matter is a particular concern to human health, as the particles are small enough to penetrate deep into the lungs.

3.1 Relevant pollution Limit Values

The table below shows the legal limits for NO2 and PM for local authorities in England as set out in the Air Quality Standards Regulations 2010. Also shown are the 2021 WHO guidelines.

3.2 Daily Air Quality Index (DAQI)

The Daily Air Quality Index (DAQI) provides information on air pollution levels, recommended actions, and health advice. The index is numbered 1-10 and divided into four bands, low (1) to very high (10). More information on the AQ Index can be found on the Defra UK AIR website.

Boundaries

Band DAQI O3 NO2 PM2.5 PM10
Low 1 0-33 0-67 0-11 0-16
2 34-66 68-134 12-23 17-33
3 67-100 135-200 24-35 34-50
Moderate 4 101-120 201-267 36-41 51-58
5 121-140 268-334 42-47 59-66
6 141-160 335-400 48-53 67-75
High 7 161-187 401-467 54-58 76-83
8 188-213 468-534 59-64 84-91
9 214-240 535-600 65-70 92-100
Very High 10 241 or more 601 or more 71 or more 101 or more

Health Effects

AP Band Accompanying health messages for at-risk individuals Accompanying health messages for the general population
Low (1-3) Enjoy your usual outdoor activities. Enjoy your usual outdoor activities.
Moderate (4-6) Adults and children with lung problems, and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity, particularly outdoors. Enjoy your usual outdoor activities.
High (7-9) Adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms. People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion. Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors.
Very High (10) Adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often. Reduce physical exertion, particularly outdoors, especially if you experience symptoms such as cough or sore throat.

4 Data Analysis

4.1 Summary statistics

The following tables present some basic pollutant statistics for the period selected in the report.

NO2

Figure 2: NO2 exceedence.

PM2.5

PM10

4.2 Boxplots

NO2

PM2.5

PM10

4.3 Time series plot

The plots below show the time series of concentrations each hour. Each pollutant is presented on a different tab and all sites are shown on each plot for comparison.

The plot is interactive and you can change what is shown by the following:

  • All data can be seen by clicking on the “all” button.
  • Zooming in on specific periods can be done by dragging a box over the section of the main plot.
  • Holding the mouse over the lines will highlight specific values and time stamp for that record for each site.
  • Double-clicking on a site in the legend will show the time series for the selected site.
  • To return to the default (all data), double click the plot.

NO2 Hourly

Figure 3: Time series plot of hourly average NO2 concentration.

NO2 Daily

Figure 4: Time series plot of daily average NO2 concentration.

PM2.5 Hourly

Figure 5: Time series plot of hourly average PM2.5 concentration.

PM2.5 Daily

Figure 6: Time series plot of daily average PM2.5 concentration.

PM10 Hourly

Figure 7: Time series plot of hourly average PM10 concentration.

PM10 Daily

Figure 8: Time series plot of daily average PM10 concentration.

4.4 Variations with time

The plots below show how the concentrations vary with hour of the day and day of week. These plots often help explain variations in concentration according to the emissions activity associated with them. For example, NO2 concentrations at roadside locations tend to show peaks in the morning and afternoon traffic rush hours and tend to decline over weekends when there is generally lower traffic volumes. For PM2.5 a peak often occurs later in the evening, which is likely due to emissions from domestic burning of wood for heating.

Similar to the the time series plots above, this plot is interactive. To select one site, double click on the site in the legend. Further sites can then be added with a single click. To return to all sites, double click again on the legend.

NO2

Figure 9: Time variation of hourly NO2 concentrations.

PM2.5

Figure 10: Time variation of hourly PM2.5 concentrations.

PM10

Figure 11: Time variation of hourly PM10 concentrations.

4.5 Calendar plot

The plots below show daily variation in concentrations by pollutant and site (one on each tab) across the period of the report, as laid out in a calendar style. This allows intuitive viewing of day to day headline trends in the wider context of the period. The background colours shown for each day relate to the concentration. The actual concentrations, along with the wind speed, can also be seen by hovering the mouse on the cell.

PM10

1st Charlton Scouts, Shepperton (sensor)

Figure 12: PM10 calendar plot.

1st Sunbury Scouts, Sunbury (sensor)

Figure 13: PM10 calendar plot.

Knowle Green Council Offices (sensor)

Figure 14: PM10 calendar plot.

Shepperton Squires Bridge Road (sensor)

Figure 15: PM10 calendar plot.

Staines Bus Station Bus Stand 3 (sensor)

Figure 16: PM10 calendar plot.

Sunbury-on-Thames St Ignatius School (sensor)

Figure 17: PM10 calendar plot.

NO2

1st Charlton Scouts, Shepperton (sensor)

Figure 18: NO2 calendar plot.

1st Sunbury Scouts, Sunbury (sensor)

Figure 19: NO2 calendar plot.

Knowle Green Council Offices (sensor)

Figure 20: NO2 calendar plot.

Shepperton Squires Bridge Road (sensor)

Figure 21: NO2 calendar plot.

Staines Bus Station Bus Stand 3 (sensor)

Figure 22: NO2 calendar plot.

Sunbury-on-Thames St Ignatius School (sensor)

Figure 23: NO2 calendar plot.

PM2.5

1st Charlton Scouts, Shepperton (sensor)

Figure 24: PM2.5 calendar plot.

1st Sunbury Scouts, Sunbury (sensor)

Figure 25: PM2.5 calendar plot.

Knowle Green Council Offices (sensor)

Figure 26: PM2.5 calendar plot.

Shepperton Squires Bridge Road (sensor)

Figure 27: PM2.5 calendar plot.

Staines Bus Station Bus Stand 3 (sensor)

Figure 28: PM2.5 calendar plot.

Sunbury-on-Thames St Ignatius School (sensor)

Figure 29: PM2.5 calendar plot.

4.6 Back trajectory analysis

The back trajectory plot shows data from the HYSPLIT model run in analysis mode. This shows the air mass back trajectories for the period covered by the report. Three different kinds of plot are shown. One statistically groups the trajectories into similar clusters and shows the proportion of time during the report period that each represents. This is useful to get an overview of air mass origins during the report period. On additional tabs, the trajectories associated with exceedances of the limit value (24-hr for PM10) is shown. A plot of the trajectories associated with the top 10 measured concentrations is also presented.

Trajectory clusters

4-day air mass back trajectories arriving at London for 2023 are grouped into 6 clusters.

Trajectories associated with pollutant exceedances

There were no NO2 hourly exceedances.

Daily PM10

Trajectories for days when there was an exceedence in PM10 concentration are plotted below.

4.6.1 Trajectories associated with top ten most polluted days {-}

The average daily concentration for each pollutant across all the sites was calculated. The top 10 most polluted days were identified and linked to the back trajectory data.

NO2

PM2.5

PM10

4.7 Polar plot map

The plot below shows bivariate plots, ‘’pollution roses’’ of hourly mean pollutant concentrations against the corresponding wind speed and wind direction. These plots should be interpreted as follows:

  • The wind direction is indicated as in the wind rose above (north, south, east and west are indicated).

  • The wind speed is indicated by the distance from the centre of the plot: the concentric circles indicate wind speeds in 5 ms-1 intervals.

  • The pollutant concentration is indicated by the colour (as indicated by the scale).

These plots therefore show how pollutant concentration varies with wind direction and wind speed.

The plots do not show distance of pollutant emission sources from the monitoring site. However, in the case of primary pollutants such as NO, the concentrations at very low wind speeds are dominated by emission sources close by, while at higher wind speeds, effects are seen from sources further away.

NO2

PM2.5

PM10



For further information, please contact:

Name Ben Fowler
Address Ricardo Energy & Environment, Gemini Building, Harwell, Didcot, OX11 0QR, United Kingdom
Telephone 01235 753554
Email