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. 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 audio experience for the rider.

The data also builds a more 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 averaged readings are reported.


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 users of the city who spend lots of time in these hotspots, living or working. For our sonifications, it provided high peaks to take into account alongside a lower range of figures that undulated much 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 the air pollution data together with GPS locations. This allows us to chart the pollution onto maps, to show where these PM2.5 hotspots were.  Using 3D visualizations we displayed the quantity of air pollution along these routes on interactive maps. The height of the red line indicates the volume of PM2.5 pollution – higher equals more pollution.

3d visualization of pollution

What we found through Environmental sonic biking

Cyclists in Lisbon could ride the Environmental bikes wherever they liked – along familiar routes, around their homes or workplaces, along busy roads or through quiet parks. This collected a huge amount of data across different locations and at different times.

3d visualization of pollution

Through conversation with riders, from our own sonic cycling experiences and through our exploration of the data, we found out lots about the nature of air pollution and how it fills Lisbon. Including;

  • finding certain hot spot areas of constantly high pollution, often around junctions (cars starting and stopping?)
  • busy road 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 subways / certain vehicles / extraction units)
  • narrow roads with high buildings seemed to trap the PM2.5, which was particularly unexpected as these were often car free quiet places
  • that PM2.5 moves in gusts or bubbles – it would pass over one bike and then the next, which we could 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.
  • pollution was higher at night, often near restaurants and bars – 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 much more to investigate through study of the data too. One finding is apparent from our readings so far – that averaging  air pollution data looses these significant peaks of pollution….. the figure for peaks need to also 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 through this sonic cycling experience was pretty exciting!

3d visualization of pollution
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