Wiltshire Monthly Report
Monthly report for January 2020
| Authors | Hao Wu |
| Compilation date | 05 February 2020 |
| Customer | Wiltshire County Council |
| Approved by | Ben Davies |
| Copyright | Ricardo Energy & Environment |
| EULA | http://ee.ricardo.com/cms/eula/ |
| Contract reference | ED62771 | Report reference | January 2020 |
1 Introduction
This is a monthly summary report for Wiltshire County Council for the period 2020 January.
This is a dynamic report containing embedded data from which the report tables, plots and graphs are generated. The embedded data allows the reader a level of interaction with some of the report findings, providing additional insight. This approach enables a more easily navigated and streamlined report providing an engaging and intuitive reader experience.
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 . Full site information can be obtained using the URL hyperlink in the popup for each monitoring station on the map.
3 Data description
Data contained within this report is managed by Ricardo and stored in a dedicated, secure database. The data within this report is provisional and subject to change, and as such should be treated with caution.
Some of the plots provided in this report use associated meteorological data (typically wind speed and wind direction) in order to show measured pollutant concentrations in a dispersion context. Very few monitoring stations provide quality controlled met data, therefore these reports import data from the Met Office DataPoint 1.
Gaseous pollutant mass units are at 20 °C and 1013mb. NOx mass units are NOx as NO2 μg m-3. Particulate matter concentrations are reported at ambient temperature and pressure.
3.1 Relevant pollution Limit Values
The European Air Quality Directive and Fourth Daughter Directive set out legal limits for different pollutants as Limit Values, Target Values or Long Term Objectives to protect human health. These are summarised in the table below. Local authorities don’t typically measure ozone, benzene, B[a]P or metals that are captured within Defra’s national networks. All pollutants measured have been included in this data summary for completeness, irrespective of their significance for local authority policy interests.
4 Data Analysis
4.1 Summary statistics
The following tables present pollutant statistics for the period from the start of the year to the reported month. The Low, Moderate and High indicates the number of days for a particular pollutant when the concentrations are in the corresponding AQI bands from the beginning of the year until the end of the reported month.
NO2
PM10
PM2.5
4.2 AQ index distribution
The plots below illustrate the distribution of AQ index values for each site by pollutant. It shows the number of days that site concentrations are in each index. More information on the AQ Index is available from UK-Air 2.
NO2
Figure 1: Distribution of AQI for NO2.
PM10
Figure 2: Distribution of AQI for PM10.
PM2.5
Figure 3: Distribution of AQI for PM2.5.
4.3 Boxplots
The plots below are box and whisker plots to show the distribution in concentrations for each monitoring station. The boxes demarcate the lower quartile, median and upper quartile. The whiskers extend to the maximum and minimum values within median ± 1.5 times interquartile range (IQR). Values outside the median ± 1.5 times IQR are generally considered as outliers.
NO2
Figure 4: Boxplot for NO2 concentration.
PM10
Figure 5: Boxplot for PM10 concentration.
PM2.5
Figure 6: Boxplot for PM2.5 concentration.
4.4 Time series plot
The plots below show the time series of concentrations. Each pollutant is presented on a different tab and all sites are shown on each plot for comparison. A daily average resolution has been chosen as the most appropriate metric over a variety of different time windows. Zooming in on specific periods of the plot can be done by dragging a box over the section of the main plot frame or by using the sliders in the narrow plot frame below. To return to the default (all data) zoom level, double click the plot. Holding the mouse over the lines will highlight specific values and time stamp for that record for each station.
NO2
Figure 7: Time series plot of daily average NO2 concentration.
PM10
Figure 8: Time series plot of daily average PM10 concentration.
PM2.5
Figure 9: Time series plot of daily average PM2.5 concentration.
4.5 Time Variation plot
These plots show concentrations over different time intervals such as diurnal, day of week and month of year. The plot showing seasonal variation will show only the three months of the quarter or a dot showing one month depending on the time frame covered in this report. The topmost frame shows the concentrations as they vary by hour of the day and day of the week. The hour of the day variation is summarised on its own in the lower left pane and the variation by day of the week is shown in the lower right pane. These plots often help explain variations in concentration according to the emissions activity associated with them. For example, NOx concentrations at roadside sites tend to exhibit peaks according to morning and evening traffic rush hours and tend to decline over weekends when there is generally lower traffic volumes.
NO2
Figure 10: Time variation of hourly NO2 concentration.
PM10
Figure 11: Time variation of hourly PM10 concentration.
PM2.5
Figure 12: Time variation of hourly PM2.5 concentration.
4.6 Calendar plot
The plot below shows daily variation in concentrations by pollutant (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 date is coloured by the wind speed for that day. The actual value can also be seen by hovering the mouse on the cell.
NO2
Bradford-on-Avon, Masons Lane
Figure 13: NO2 calendar plot.
Devizes, Sidmouth Street
Figure 13: NO2 calendar plot.
Salisbury, Exeter Street
Figure 13: NO2 calendar plot.
Wootton Bassett High Street
Figure 13: NO2 calendar plot.
PM10
Bradford-on-Avon, Masons Lane
Figure 14: PM10 calendar plot.
Devizes, Sidmouth Street
Figure 14: PM10 calendar plot.
Marlborough London Road 2
Figure 14: PM10 calendar plot.
Salisbury, Exeter Street
Figure 14: PM10 calendar plot.
PM2.5
Marlborough London Road 2
Figure 15: PM2.5 calendar plot.
4.7 Back trajectory analysis
The back trajectory plot shows data from the HYSPLIT model (NOAA HYSPLIT 3) run in analysis mode. This shows the air mass back trajectories for the period covered by the report. Two 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 (Figure 16). This is useful to get an overview of air mass origins during the report period. Plots in Trajectories associated with top ten most polluted days provide information on the trajectory direction associated with the top 10 measured concentrations.
4.7.1 Trajectory clusters
4-day air mass back trajectories arriving at the sites for 2020 are grouped into 4 clusters.
Figure 16: Back trajectory clusters for the month reported.
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 Energy & Environment. The receptor point is used here is Harwell which is 50.5km away from the centre of all monitoring stations analysed in this report.
4.7.2 Trajectories associated with top ten most polluted days
The average daily concentration for each pollutant across all the sites is calculated, with the top 10 most polluted days identified and linked to its back trajectory data in the plot below.
NO2
Figure 17: Trajectory plot for top ten highest daily NO2 concentration.
PM10
Figure 18: Trajectory plot for top ten highest daily PM10 concentration.
PM2.5
Figure 19: Trajectory plot for top ten highest daily PM2.5 concentration.
4.8 Polar plot map
The maps below show polar plots for each pollutant at each monitoring station superimposed on the region to help understand the relative strength and direction of sources. The distance from the plot origin shows the wind speed.
These plots are useful to help identify primary pollutants which are emitted directly into the atmosphere, especially when multiple plots are used in conjunction to ‘triangulate’ a common source. For pollutants with a secondary component (i.e. formed through chemical reactions in the atmosphere, e.g. NO2, PM2.5 and O3) the directional signature seen in the measurements may not be as strong.
NO2
Figure 20: Polar plot for NO2.
PM10
Figure 21: Polar plot for PM10.
PM2.5
Figure 22: Polar plot for PM2.5.
| Name | Ben Davies |
| Address | Ricardo Energy & Environment, Gemini Building, Harwell, Didcot, OX11 0QR, UK |
| Telephone | 01235 753 069 |
| Ben.davies@ricardo.com |