As part of the development of the AirKit toolkit, Citizen Sense worked with participants in Forest Hill, London, to monitor air quality near Brockley Rise from January to July 2020. Collaborating with Clean Air SE 23 and the Dalmain School, Citizen Sense set up Dustbox 2.0 monitors at four locations near Brockley Rise in Forest Hill. This data story details how citizen data, weather data and local observations reveal specific pollution patterns. Drawing on meetings, conversations and workshops with local residents, the data story also suggests how best to address the problem, from planning for better transport to reducing burning practices in the area.
The key findings from this Brockley Rise Covid Data Story indicate that traffic emissions are a primary source of air pollution, although this has been lessened somewhat by the first national lockdown due to Covid-19. There were noticeable drops in air pollution in London during the lockdown, especially of NO2. However, declines in particulate matter were less pronounced during this time. We discuss these findings in more detail in a related Covid Data Story, Forest Hill Lockdown.
1. The Location
The Brockley Rise monitoring location includes Dustboxes 2051, 2058, 2060 and 2062. These Dustboxes can be viewed and analyzed on the Citizen Sense Airsift platform. There are several schools in the area, and land use is primarily residential, with localised concentrations of shops, parks and restaurants. Several busy roads cut through Brockley Rise, including the main A205 artery (the South Circular Road). These busy roads contribute to transport as the main source of pollution in the area.
The above map indicates the approximate monitoring locations of the Dustboxes. Dustboxes 2051 and 2060 were located in a non-residential area at the Dalmain School. Dustbox 2060 faced the Brockley Rise road and Dustbox 2051 was sheltered within a DIY Stevenson screen in a building close to the Brockley Rise road. Dustboxes 2058 and 2062 were both located in separate residential gardens and sheltered within DIY Stevenson screens.
Local sources of particulate pollution
The transport sector is the major source of particulate pollution around the Brockley Rise area. The South Circular Road is one of the busiest roads in London, which along with the North Circular Road and Woolwich Ferry, forms a ring road around Central London. There are several intersections along the South Circular that lead to traffic congestion and an increase in vehicle emissions. Other potential sources of pollution include train stations that are traffic hubs and drop-off points, including Honor Oak Park, Forest Hill, Catford and Crofton Park. Additionally, potential emissions sources include outdoor burning, especially to the north of the monitoring site.
London-wide, regional and global sources of particulate pollution
Particulate matter sources in London can be attributed to a broad range of emissions. Within London, PM2.5 from transport (particularly diesel), industry, construction, cooking and heating all contribute significantly to London-wide levels. A significant amount of PM2.5 emissions also comes from heavy industry and agriculture outside the UK, particularly France, Belgium, the Netherlands, Luxembourg, Germany and Poland. These emissions are thought to account for an urban background of approximately 10 µg/m3. The importance of these transboundary effects of PM2.5 emissions from outside of the UK on the total London PM2.5 can vary between 40 to 80 percent daily depending on weather conditions. When long-range pollution episodes do occur in London, they are generally carried on easterly winds. There are a number of global emissions events and practices that contribute particulate matter to the total London PM2.5, including fuel production, industrial and domestic combustion, transportation, waste disposal, and agriculture, although these are harder to quantify.
During meetings with Clean Air SE23, some observations were shared by the group members about noticeable increases in burning activities, including burning garden waste and having barbecues during the lockdown. The London Fire Brigade also reported a 7.4 percent increase in outdoors fires during the April lockdown.
2. Is there evidence of a problem?
The Dustbox 2.0 device used to monitor PM2.5 is an “indicative” monitor. This means that measurements can give an indication of pollutant concentrations, but cannot be directly compared with national and international guidelines and standards in an “official” or regulatory sense. Despite this, indicative monitors are a well-established method within atmospheric science for carrying out initial surveys of an area to establish whether a potential problem merits further investigation. Indicative monitors are also becoming increasingly available for citizen-based air-quality monitoring, similar to this study.
Where possible, the Dustboxes were co-located at the start and the end of the study to account for differences in the sensors and drift during the monitoring period. As discussed below in Figures 9 and 10, the co-location of Dustboxes with the London Air Quality Network (LAQN) New Cross Gate reference monitor indicates that there is a good similarity in measurements across the monitors used in this monitoring location, as well as with monitors in the extended community network, both at the start and end of the monitoring period.
Dustbox monitoring in the Brockley Rise location was first set up on 27 January and ran until December 2020. However, monitoring primarily took place between 07 February 2020 to 30 June 2020, and the analysis of citizen data focuses on this central monitoring period. For additional data stories that focus on the latter part of the monitoring period, see the Airsift Data Stories. Indicative daily concentrations of PM2.5 for monitors 2051 and 2060 between February 2020 and June 2020 are provided in Figure 1.
The World Health Organisation (WHO) has established a 24-hour mean guideline for PM2.5 of 25 µg/m3 (although there is no safe level of exposure). The time series graph in Figure 1 shows that the overall concentration of particulate matter remained below the threshold for both Dustboxes during the data collection period. However, there was an increase in daily PM2.5 levels during mid-March and mid-April. This was the result of two regional and London-wide pollution incidents between 25-27 March 2020 and 8-12 April 2020. The March pollution episode was mainly caused by agricultural emissions originating from Eastern Europe. The April pollution episode was mainly caused by agricultural pollution sources in Holland, Belgium and Northern France. The result was a combination of particulate pollutants from Europe accumulating along with stagnant emissions in London.
During the monitoring period, air quality data from the Dustboxes was compared with the LAQN regulatory monitor at the nearby Honor Oak Park site. This monitor is an urban background location that is stationed at locations away from direct pollution sources and is broadly representative of city-wide background concentrations. The results in Figures 2a and 2b show a similarity between patterns recorded by the LAQN monitor and the Dustboxes although the overall emissions recorded by the Dustboxes were marginally lower than the LAQN monitor because of the distance between the Dustboxes and the LAQN Monitor. Figures 3a and 3b show a comparison and similarity in patterns recorded by the Dustboxes and the LAQN monitor during the two pollution episodes.
3. Characterizing the problem
When is the source most evident?
Using time plots, it is possible to analyse the time of day, week and month when pollution levels are elevated. Time plots aggregate PM2.5 concentrations according to time, so that key patterns such as rush hours and traffic, as well as possible construction or industry sources, along with regional pollution events due to seasonal variation, are evident.
Figure 4 shows a gradual increase in PM2.5 concentration (2 to 3.5 µg/m3) during early morning hours and evening hours. This increase can be associated with traffic-related patterns at peak hours. It can be observed that the concentration levels are higher on Wednesdays, Thursdays and Fridays throughout the monitoring period. This is perhaps to be expected given that the monitoring period includes multiple London-wide pollution events that occurred in the latter part of the working week.
Which direction is PM2.5 coming from?
Wind direction has a considerable influence on pollution measurements. A sensor will only record emissions from a particular source or activity if the wind blows it from the source towards the sensor. Therefore, we can investigate where a source of pollution is likely to be located by plotting wind direction against pollution concentrations. In these polar plots, colour contours reflect pollutant concentrations in relation to wind direction and wind speed. Calm conditions (zero wind) are shown in the centre, increasing to 6 metres per second (ms-1) at the outer ring. The highest mean concentrations are shown in red, the lowest are in blue.
Figures 5a and 5b suggest that local sources of particulate matter could be present, as potentially indicated by the elevated particle concentrations at low wind speeds. The highest pollution concentrations were experienced with low wind speeds from the east, indicating a pollution source immediately to the east of the Dustbox 2051 and 2060 monitoring locations. The Brockley Rise road (B218) is immediately to the east of the school, and is the most likely pollution source detected by the Dustboxes 2051 and 2060. It can also be observed that there is potential emissions source in the northwest direction. Local observations by Clean Air SE23 suggest that notable burning activities were taking place at an allotment in this area, and this activity could have led to elevated pollution levels. However, it would require further observation and monitoring to determine the source of pollution from this location.
Figures 6a and 6b demonstrate that although Dustbox 2058 and Dustbox 2062 are both located in gardens and sheltered within DIY Stevenson screens, they still show that locally-sourced particulate matter could be present, as potentially indicated by the elevated particle concentrations at low wind speeds. Dustboxes 2051, 2060 and 2062 show similar elevated concentration patterns due to easterly winds. For Dustbox 2062, the intersection at A205 (South Circular Road) could potentially be a source of pollution as elevated levels are most evident immediately to the north of the monitoring location. It is also interesting to note that polar plots for all the Dustboxes show a potential emission source in the northwest direction, which could relate to burning activity as noted above.
Under which weather conditions are PM2.5 levels most evident?
In Figure 7, the scatter plot shows that elevated levels of pollution are recorded at lower wind speeds. This pattern also demonstrates that particulate matter is locally produced, and is not traveling from regional or more distant sources at higher wind speeds.
Comparison with other LAQN monitors
Figure 8 shows a comparison of Dustbox 2060 data with the LAQN reference monitor at New Cross Gate. The LAQN New Cross Gate monitor is a roadside monitor and is positioned 6 meters from the road at a height of 3 meters. The area is characterised by several busy roads that cross southeast London. This explains why pollution levels are higher at the LAQN New Cross Gate monitor. However, pollution patterns are broadly aligned across the Dustboxes and the New Cross Gate and Honor Oak Park reference stations, which suggests that regional pollution sources are similar at the two monitoring locations.
Co-locating the Dustbox and LAQN New Cross Gate monitor
Between 13 February to 6 April 2020, Dustboxes 2054 and 2056 were co-located with the LAQN New Cross Gate monitor. Both Dustboxes were located in the open air at a height of approximately 3 meters. The LAQN New Cross Gate monitor is stationed at roadside and is positioned 6 meters from the road at a height of 3 meters.
Figure 9 shows a comparison of the variations captured by Dustboxes 2054 and 2056. To show how the Dustbox data compares with the LAQN monitor at the same site, line graphs are plotted for comparing the data. Figure 10 shows the daily average data of Dustbox 2054 and LAQN New Cross Gate monitor. It can be observed that the variations captured by Dustbox 2054 are very similar to the LAQN New Cross Gate monitor readings. To understand the relationship between the values, statistical methods were used to calculate the Pearson correlation and it was found to be 0.95. A value closer to +1 suggests positive linear correlation and higher accuracy.
Figure 11 shows the daily average data of Dustbox 2056 and LAQN New Cross Gate monitor. It can be observed that there are some sudden peaks around late February and early March that only appear in Dustbox 2056 data. Such outliers can be caused due to various reasons like voltage fluctuation, bug stuck in the fan or even due to water droplets. The Pearson correlation was found to be 0.8 between Dustbox 2056 and LAQN New Cross Gate data.
4. Drawing the evidence together
Using the tools provided through the Citizen Sense Airsift Data Analysis Toolkit, we have analysed the Dustbox 2.0 PM2.5 data for the Brockley Rise area in Forest Hill, South East London. We have also drawn on citizen observations, datasets and tools from nearby LAQN referenice monitors, along with research from King’s College London ERG on air pollution and the first UK lockdown. Our observations are as follows:
- While regional sources of particulate matter pollution were detected, there was clear evidence of additional local source or sources at some locations, most likely related to road traffic, based on the analysis of line graphs and polar plots.
- Particulate matter pollution levels are relatively low throughout the Brockley Rise area, and are generally below the WHO 24-hour mean threshold. However, patterns indicate elevated pollution levels related to traffic, which is clearly evident during times of peak traffic activity.
- Burning activities at the allotment to the northwest of the monitoring area could be a source of pollution. Further monitoring would be needed to establish whether pollution is from burning, as well as the sources and sites.
In relation to the evidence and findings from the Dustbox citizen monitoring study, preliminary actions are proposed here that take into account the neighbourhood context and existing community organisations and initiatives. These actions have been developed in consultation with AirKit participants and local area residents.
Traffic and transport
- Pursue alternative transport options for the area in order to reduce traffic on Brockley Rise and thereby reduce PM2.5 levels.
- Improve cycling and walking routes to reduce the use of cars.
- Support the implementation of schemes such as School Streets and Low Traffic Neighbourhoods.
- Ban idling of cars at local schools.
- Enhance the existing green screen at Dalmain School with additional plants to increase the vegetation mass. Increase and add green screens at the eastern and northern perimeters of the school.
- Transform the Forest Hill station parking lot into a parklet for expanded community green space and improvement of air quality. Alternative parking lots in the area could be used where car parking is necessary.
Air quality monitoring
- Due to the lockdown from Covid-19, this study was not able to install monitors in several planned locations on the South Circular Road. However, it would be useful to study this area more extensively.
- Enhance air-quality monitoring of the South Circular to study the impact of the ULEZ expansion in October 2021.
- Expand the monitoring area to include nearby districts such as Catford to ensure that traffic is not over-spilling to adjacent neighbourhoods.
- Evaluate initiatives such as low traffic neighbourhoods to examine how changing traffic patterns could increase pollution on major roads.
- While additional restrictions on burning have been in place during much of the monitoring period, it is not clear whether they are effective. Mechanisms for reporting outdoor burning could be made clearer on the Lewisham Council webpage.
- Provide greater clarity on the actions taken against persistent burners and how these policies are enforced.
The Citizen Sense and AirKit projects are led by Professor Jennifer Gabrys. These AirKit data stories were developed working in collaboration with Dr Sachit Mahajan and Dr Joanne Armitage. Thanks are due to our collaborators including:
Common Knowledge contributed to the development of the final Airsift platform. Lau Thiam Kok and Tassos Noulas contributed to the development of the data architecture that informed the first-version Airsift platform. Some plots and graphs in this data story use and adapt openair software developed by Dr David Carslaw.
The Citizen Sense Dustbox 2.0 included collaborative contributions to the materials design and 3D printing by Andrea Rinaldi, who built on an earlier Citizen Sense Dustbox 1.0 designs developed in collaboration with Francesca Perona and Helen Pritchard.
Special thanks are due to the participants and residents in the Forest Hill area of London who contributed to the development and testing of the Dustbox monitoring kit, as well as to the collection and analysis of data and communication of results to wider publics and regulators. For more information on project contributors, see Citizen Sense People.
At the start of the monitoring period, the Dustboxes were co-located with a TSI AM 520 at the University of Cambridge. The site for the co-location study was strategically chosen so that the devices could be evaluated under varying environmental conditions with variable pollution levels. For hourly averaged PM2.5 concentration, the average Pearson correlation (R) was 0.98. Because the Dustboxes demonstrated a high degree of accuracy during the co-location, no scaling factor has been applied to calibrate the devices. Because the sensors were co-located and calibrated during a time of low to moderate pollution, the scaling factor could slightly amplify higher readings in relation to the LAQN readings. However, this would require further testing to demonstrate, since when comparing Dustbox levels with nearby LAQN levels (where available), readings are often comparable. For more information, see “Dustbox 2.0 Calibration and Field Studies.”
The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 313347, “Citizen Sensing and Environmental Practice: Assessing Participatory Engagements with Environments through Sensor Technologies,” and from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (ERC Grant Agreement n. 779921), “AirKit: Citizen Sense Air Monitoring Kit.” The University of Cambridge provided additional support through the ESRC Impact Acceleration Account (2020) for enabling impact.
AirKit is available to use under a CC BY-NC-SA 4.0 license. You are free to use, adapt, and share this toolkit for non-commercial purposes under the same CC BY-NC-SA license, and with attribution to Citizen Sense.
To cite this data story, please use the reference: Citizen Sense (2020) “Brockley Rise,” Covid Data Stories, 31 December 2020. Available at: https://datastories-covid.citizensense.net/brockley-rise.