Promises & goals of the CityBreeze billboards
While a 75-inch LCD screen displays advertisements on the front of the CityBreeze Steles, a living moss wall is located on the back. According to the manufacturer, this filters out the smallest particles such as particulates, viruses, bacteria as well as odors and gases from the air. In addition, the moss binds greenhouse gases that are harmful to the climate. As moisture evaporates on the moss surface, the ambient air is even cooled by a few degrees. The billboards are powered by green electricity so that the digital advertising media leave as small a carbon footprint as possible and outdoor advertising becomes more climate-friendly and sustainable.
With its world's first regenerative bio-tech filters, the manufacturer promises a demonstrable improvement in air quality: the green billboards are said to remove up to 82 percent of the particulate matter contained in the air flowing through them. For a noticeable effect, Green City Solutions places its billboards primarily at high-traffic locations such as a shopping center, parking lots or other busy places.
We have now measured whether the CityBreeze keeps its promise.
air-Q field test: Measurable air purification & impact of CityBreeze on air quality.
We performed our test measurement in Leipzig's Plagwitz district. Here, the CityBreeze billboard is located on a busy main street next to a shopping center and a gym. The screen faces the street, while the moss wall at the back points to a house wall. A wooden bench is grouped around the billboard so that people can sit down and, at best, feel the purified air directly. So that we could understand the effects of the air purification in the outflowing air, we placed several air measuring devices at different heights in front of the advertising board. This allowed us to imitate people of different heights and check the airflow at different points.
First, we tested the ambient air in front of the ad. The test period was ten minutes in the morning between 10:26 and 10:36. We then collected measurement data on the back of the stele to test the effect of the air purifier. Here we had the three air-Qs collect measurement data between 10:40 and 10:55. In doing so, we sometimes placed them further away and sometimes as close as possible to the louvers and aligned the sensors with them to determine the direct airflow. Since the measured values are similar, we show a diagram of one air-measuring device as an example in the following - but also show the measured values of the remaining devices.
Our test does not claim to be scientifically unimpeachable. Since the billboard is located in an urban space, we could not test it under laboratory conditions. Visitors who use the bench are also in the real situation.
Can a CityBreeze Stele reduce particulate matter in the air?
Directly in front of the stele, the air-Q air measuring device was only able to detect a very low average level of particulate matter of the larger PM₁₀ particulate matter molecules of 5 μg/m³ (micrograms per cubic meter) or 6 μg/m³ (test device 2 & 3) in the ambient air. particulates is produced, among other things, by brake abrasion from cars and is very unhealthy if inhaled. The value of the smaller PM₂,₅ particles was also only 4 μg/m³ on average (test device 1 & 2). In contrast, this air pollutant does not reach a limit value of concern until 40 μg/m³. Therefore, there were hardly any pollutants suspended in the air that the filter could have removed.
Evaluation diagram PM₁₀-measured values incoming air
Evaluation diagram PM₂,₅-measured values incoming air
A difference between the quality of the incoming and outgoing air was not detectable. Accordingly, our experiment as well as the evaluation of the measurement data cannot detect or prove any effect. On the moss filter side, the same PM₁₀ measurement values of an average of 5 μg/m³ (test device 1 & 2, test device 3 determined an average value of 4 μg/m³) and 4 μg/m³ (test device 1 & 2, test device 3 determined an average value of 3 μg/m³) prevailed for the smaller particulate matter particles.
Evaluation diagram PM₁₀-measured values outflowing air
Evaluation diagram PM₂,₅-measured values outflowing air
How does the moss filter of a CityBreeze billboard affect the nitrogen dioxide content of the air?
In addition to the effect on particulates , we also observed the change in the measured value of nitrogen dioxide. Nitrogen oxides are formed at high temperatures, e.g. in engines, and enter the air through car exhausts. The incoming air at the busy road was enriched with an average of 38.81 μg/m³. In the course, the load increased from just under 30 to over 50 μg/m³, thus exceeding the limit value of 40 μg/m³ for all test devices. This shows the increase in traffic volume and thus the exposure to car exhaust during the test phase.
Evaluation diagram nitrogen dioxide measured values incoming air
In contrast, the outflowing air contained an average of only 23.84 μg/m³ (test device 1). The initial value initially fell from approx. 30 μg/m³ to just under 10 μg/m³, but then rose continuously again and also exceeded the limit value of 40 μg/m³ towards the end of the test. This development was also shown by the other test devices. Thus, we were unable to demonstrate any significant improvement in air quality in the form of purification of the incoming air containing nitrogen dioxide.
Evaluation diagram nitrogen dioxide measured values outflowing air
Does a moss filter improve relative humidity?
We also tested the relative humidity. The incoming air had an average humidity of 35.07 (test device 1), 43.99 (test device 2) and 37.89 (test device 3) percent. This was hardly subject to fluctuations and appears as a constant line in our evaluation chart.
Evaluation diagram humidity of incoming air
In the outgoing air, the air-Q was able to detect a noticeably higher average humidity of 41.77 (test device 1), 43.86 (test device 2) and 43.45 (test device 3) percent. While the measured value for test device 1 increased slightly during the practical test, it decreased for device 2 and remained relatively constant for device 3. The different heights of the positioned air measuring devices thus seem to have an effect on the air composition.
Evaluation diagram humidity of the outflowing air
Can a CityBreeze ad cool the air temperature?
The CityBreeze billboards promise a cooling effect of up to 4°C with an output of over 2,000 watts. We also collected this measured value with the air-Q. On the side of the screen, i.e. the air flowing in, the temperature fluctuated between 28 and 32°C. The air-Q determined an average temperature of 31.29 (test device 1), 26.54 (test device 2) and 29.28 °C (test device 3).
Evaluation diagram air temperature of incoming air
Since the sun fell on the advertising screen from the front during the test period, a natural shadow was created on the side of the moss wall and the ambient temperature was much lower than in direct sunlight anyway. Accordingly, we were able to determine a significant temperature difference behind the moss filter, but we could not clearly attribute this to the stele. Significantly lower temperatures were also noticeable in the shade around the advertisement. Thus, test device 1 showed an average temperature of 26.98°C, device 2 26.75°C and device 3 26.08°C.
Evaluation diagram air temperature of the outflowing air
Our conclusion to the CityBreeze test
Our measurement data showed no significant effect of the moss air filter on air quality. We could therefore neither feel nor measure an air-purifying effect. However, in our tested billboard, the moss used was very dried out in many places and did not cover the back wall in a comprehensive manner. Therefore, it is possible that the moss wall did not work adequately. According to the manufacturer's website, the walls are regularly maintained - the interval for this would therefore have to be greatly reduced to ensure functionality at all. We did not hear anything about the manufacturer's advertised "smart watering system".
Since the billboard is not short-meshed, the question arises whether the functionality of the moss wall is the focus of the operator at all. Possibly, the functionality of the billboard and the sale of advertising space under an ecologically justifiable label is rather the goal.
We also noticed that both the location and the construction of the bench do not necessarily invite you to linger. We noticed a lot of noise pollution from the traffic. Do people want to linger on a busy road in an industrial area and enjoy the "fresh breeze"? Or do you just want as many drivers as possible to notice the advertising message?
So how green are CityBreeze really, or is it greenwashing? After all, the displays claim to be the first truly green advertising network. The appeal of this advertising slogan could also have an effect on the companies and products presented here.
During our field test, we were also concerned with other questions. For example, why isn't the electricity for the advertising screens generated by the steles themselves via solar panels? How many billboards would you have to put up in a city to really provide better air? And why are the benches designed so that those sitting, instead of looking toward the air cleaner, turn away from it? If the direction of sitting were towards the filter, the lingering people would be able to breathe in the filtered, fresh air much more easily.
In addition, the manufacturer of the CityBreeze stands states on its own website that the air quality sensor measures filter performance and environmental data and would display it in real time. Perhaps this is done on an external platform. However, the data is not displayed on the stele itself and, unfortunately, no indication is given as to where the data can be viewed. We would have very much liked to compare the data from the air quality improvement board with the measurement data from the air-Qs at the same time.
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