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Using Smart Citizen Kits to track COVID-19 effect on pollution

Hi everyone!

First of all, we hope that you are all doing good given the current situation.
We just wanted to share with you that last week we published a little analysis of the effect of COVID-19 lockdown on pollution with open data from the kits deployed around Barcelona. We also included some other kits and we are cooking a bigger analysis, but for starters this is it:

The code that generated this is also open and can be accessed in this github repo.

We see this moment is an exceptional worldwide experiment and an opportunity for change and we would like to hear from you and see how things are evolving in other parts of the world. Have you seen changes in the data from your sensors? Are you planning on measuring something yourselves to see how this period affects the environment?

Hope you like it and looking forward!


That’s a really great article. Its such a pity we see so few kits in my part of the world. (Australia and Asia more generally)

Hi all!

In our twitter account (@fumutsrosolano) we have also been using the sensor to communicate the COVID effects on pollution in our neighbourhood. But while the noise data logically correlates with confinement periods, we have the opposite for PM2,5: higher concentrations during confinement and OK levels the last weeks (when activity and cars have returned to the street).

Anyone has thoughts on why is this happening in our case? Specially @oscgonfer and rest of the team in Barcelona.


Some thoughts.
Firstly are you kit(s) indoor or outdoor ?
If they are indoor, cv19 confinement will correlate with people choosing to cook meals at home. I have found my own PM x levels increase at meal times. TVOC also increases for same reason.

If they are outdoor and its winter then people using wood burning fires to heat homes (because they are at home) will cause increase in particulates. Even in summer they might light fireplaces at night because its cosier.

In summer time it might be that people < shock horror > might be burning garden vegetative waste, generated because people spend time tidying their garden when confined at home.
In some places in the world summer coincides with increase in particulates as people burn farmland vegetation and undergrowth.

These suggestions might not work where you are but maybe it will help generate some ideas for you…


Greetings from la Garrotxa,

I think that we need to take into account other factors such as rain, wind, etc. during previous days that may have altered a nice looking drop in air pollution. I looks more logical when you see CO2eq instead of PM2.5.


Thank you both @bryn.parrott and @doktorkampi for your time and answers!

@bryn.parrott: our kit is outdoors, located in a very dense historic neighbourhood with narrow streets (8 m aprox.) and mainly condominiums (no gardens or fireplaces). So even if your hints could be useful in other contexts, cannot explain this situation. Thanks anyway! :slight_smile:

@doktorkampi: yes, I guess weather is the answer. April was an specially rainy month in Barcelona this year, so it could be wind from the Sahara that influenced the measurements…
Regarding CO2eq, I’ve never payed much attention to this variable, since I had read somewhere in the manuals, that it was not such an accurate tool… Am I wrong? According to your experience, do you actually use it in order to assess pollution? I usually rely on the PM2,5 values, but it could maybe also be an interesting variable to communicate to people


Hi Xavi,

In my opinion, CO2eq is not a good parameter to assess air quality in terms of human health, but an indirect indicator of greenhouse gases emissions, which at the end may be harming our planet and therefore our species. When we look at PM2.5 we can easily correlate to a particular level of air pollution that we breathe, whereas CO2eq may indicate the amount of certain emitted pollutants. In this particular case, we observed a sustained decrease in CO2eq after the lockdown in Olot, but particulate matter was harder to correlate to regular activities that may pollute such as road traffic.

Hope that this helps.



It’s really nice to see that you are getting to these conclusions. This article talks about the effects of weather conditions in a study using SCKs carried out in Bologna (similar weather as Barcelona with some differences in winters). If you refer to pages 14-15 the discussion about these topics is explained, and the results in April could be somehow explained, keeping in mind that we have not used the SCKs in the same controlled way as this study, as we do not know the exact exposure for each device.

With respect to CO2eq, consider it a proxy to volatile organic compounds (CO2eq and tVOC are the same), and mostly indicate as @doktorkampi says, human activity that puts in the atmosphere substances that contain highly volatile substances such as solvents, paints,… Is it a definite measurement? No. However, it can be used with other variables (T, H, PM…) to understand trends in the data.


@oscgonfer I think many people do not understand the term eCO2. What it is NOT is a measure of the gas CO2 in air. It is a proxy for TVOC which is measurement of a bundle of different gases often not specified.
This is why having the NDIR CO2 sensor available as optional sensor is important, because it measures actual CO2 gas concentration.
Thus the expected level is just above 400 Ppm (anywhere in the world) at the moment but rising as time goes by.
But in short time frames the level can increase in a given area, for example when gas cooking is happening indoors, with windows all closed, or if you live in Oregon or Vancouver right now, it might reflect wild fires, and correlate with high PM readings.
When a source of excess CO2 goes away then elevated levels in the vicinity can be expected to settle back to the long term wide area value.

A further note that CO2 is not the only greenhouse gas, CH4 methane is an order of magnitude more significant. A full scientific study using the SCK in this specialist area would need to add a methane sensor too. Generally the concentration at sea level is very low, unless you live near a source such as swamp, garbage dump, farm etc. Indoors, flatulence is the main source.

@doktorkampi Its funny you should say that. I have the same idea (to add wind and rain sensors).

I am currently working on an enhanced version of SCS that has both types of extra sensors added. It uses ultrasonic wind sensor ULP from Calypso Instruments and Infrared Rain sensor RG15 from Radeon. No moving parts in either sensor.

These sensors are NOT cheap, it increases the cost of the system significantly. Eg + ~$USD 800 and I guess this is a good reason why these features are not standard. Of course there are much cheaper sensors available.

It’s not ready for prime time just yet. If you are interested I intend to make some details available when it’s all working.


Hi Bryn,

Maybe this helps? eCO2/TVOC - Smart Citizen Docs

Regarding NDIR sensor, totally agree, that’s why we support the Sensirion SCD30 sensor: CO2 sensor - Smart Citizen Docs.

Regarding VOCS, it is true that we do not have a full setup for them. Not only CH4 but other formaldehyde, benzenes, toluene, etc… to identify a proper pollutant profile would be important. This would allow us to make the connection between human activities and pollution with more precision.


The Doc you referred to gives a pretty good rundown. It’s a pity more people do not read all the way through the docs! It’s human nature I guess.

As you are aware there are many other VOC sensors out on the market of which BME680 made by Bosch is one, and it’s supported by SC too.

I am, as you are aware, also evaluating another which is ENS160 Made by ScioSense who also make the CCS811. The main difference is that this new device has 4 MOX heated plates instead of 1, and the documentation provides characterisation of the sensors response to specific VOC gases. And the range of gases included is somewhat wider. But that’s not to say it provides a measurement of each one by name, it still lumps them together as TVOC.

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