Air Pollution: the data and our visualisations
The air pollution sensor and what it collects
The air pollution sensor used on Environmental Bike is the ‘Digital universal particle concentration sensor’, advised by Sonic Kayak team Dave and Amber at FoAM Kernow, who also designed its 3D casing.
Of the 9 different data readings that the sensor provides, we have been focused on the following three:
- 2.5> concentration. This measures how many fine particles of 2.5 micrometers and smaller are in the air – all of the super fine harmful stuff that gets into our lungs and bloodstream. Known as ‘PM2.5’ this is a key pollutant that is a real problem in urban spaces.
- 0.3< concentration. This measures the particles of 0.3 micrometers and larger. This captures both pollutants and organic matter like pollen. It provides a dynamic data set which is good for sonification.
- 0.5< concentration. Particles of 0.5 micrometers and larger. As above.
How much pollution is in Lisbon’s air?
During the Lab the four Environmental Bikes were ridden all over the city by the participants and by ourselves. On each ride the air pollution was live sonified for riders so they could hear the pollution levels as they rode also providing a unique sonic bike experience on every occasion. This map shows a number of the routes taken.
EnviroBikes also record this data as they go so it can be reviewed afterwards. Understanding the data and quality of the air enables us to build and improve the bikes’ sonification responses creating a more comprehensive and interesting audio experience for the rider.
The data also builds a detailed understanding of the quality of Lisbon’s air – showing how much harmful PM2.5 there is at any given moment. This builds on the data provided by the government, who use static monitoring sites, from which only averaged readings are reported from these fixed locations.
This graph shows a selection of the bike rides made from just one of the four Environmental Bikes during the lab.
Each line shows the duration of the bike ride. The horizontal axis shows time (how long they rode for) and the vertical axis counts PM2.5 concentration (how polluted the air was). The blue horizontal line at 25 shows the EU’s target for PM2.5 reduction.
How much is too much? Ideally there would be no PM2.5 in the air, as it is harmful to us. The horizontal blue line showing the EU’s target, is an annual averaged figure that cities need to be below each year. During our Lab (in September 2020) the PM2.5 levels in Lisbon sat mainly between 0-10 in and around the city – so reasonably low. However, on almost every ride the cyclist would also ride through one or more hot spots of PM2.5 pollution, causing peaks up to 25 and even far over it reaching the 90s. This has significant health implications for city users who might regularly pass through these hotspots in their daily lives without realising. For our sonification responses, the hotspots provided peaks to take into account alongside a lower range of figures that undulated more gradually.
How we visualized the air pollution for riders
When riders returned to the Lab, we would show them two visualisations of their ride and what they had just experienced through sound. Firstly a graph showing the levels of PM2.5 they rode through, with the EU limit included for context.
The bikes also log their journeys’ GPS locations along with the air pollution data as they go. This allows us to chart the changing pollution levels onto maps also showing exact locations of the mentioned PM2.5 hotspots. Using 3D visualizations we then displayed this quantity of air pollution along these routes where the height of the red line indicates the volume of PM2.5 pollution. So the higher the red line, the more pollution.
What we found through Environmental sonic biking
Cyclists in Lisbon chose to ride the Environmental bikes wherever they liked. Maybe along familiar routes, around their homes or workplaces, or just exploring busy roads or quiet parks. This collected a huge amount of data across different locations and at different times of day.
Through conversation with the riders, from our own sonic cycling experiences and through our exploration of the data, we came up with many questions about air pollution and how it moves and changes, not only with location and volumes of traffic/trees/ architecture, but with the time of day and the weather in Lisbon. We also discovered much including :-
- finding certain hot spots of constantly high pollution, often around junctions (cars starting and stopping?)
- busy roads didn’t spike as much as we expected (other pollutants may have increased significantly, but PM2.5 only rose slightly)
- unknown passing sources caused hugely high dangerous spikes (maybe pavement vents from subways / certain vehicles / air extraction units)
- narrow roads with high buildings seemed to trap air and therefore PM2.5 levels rose, which was particularly unexpected as these areas were often car free and quiet
- that PM2.5 moves in gusts or bubbles , ie. it would pass over one bike and then the next, which we could all hear from our ‘sonic alarms’ for high pollution being triggered.
- parks were not always free from pollution, high levels would gust through – possibly from passing vehicles around the edge or pollen from the trees?
- pollution was higher at night, often near busy restaurants frying fish on charcoal/bars full of happy smokers/ a specific Hotel on a major inner highway – their extractor fans perhaps ?
- completely unknown sources triggered high levels of pollution that we just couldn’t match to anything in our surroundings. Was it simply moving in the air? Or are there causes that we have no idea about?!
There is also much more to investigate through study of the data. One finding is apparent from our readings so far – that averaging air pollution data loses these significant peaks of pollution. The figures for peaks also really need to be included in data reporting from official monitoring stations to understand the full range of what is in the air.
The Environmental bikes are offering a unique method of air pollution investigation. Riders found the experience to be exhilarating and empowering – to be able to understand the quality of the air they were riding through inspired a very different way of riding and listening. No longer were they simply floating through space listening, but were out seeking air pollution by what they heard and truly engaging with the air space and city around them therefore in a new way.