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NO2 sensors missing

Very disappointed that the V2 kits don’t have the NO2 sensor (as the V1 kits did). Didn’t know until we have received the kits that they didn’t. This is probably the most useful pollutant measurement and is used by UK government and local authorities, When will you make an NO2 sensor available, at the moment this has very limited use and seems to have gone backwards since the V1 kits

Dear Andy,

Thanks for posting your opinion.

We have an explanation for this decission in this page of the documentation. TL;DR: the results from the previous metal oxyde sensors for targetted pollutants were not satisfactory, and we decided to simplify the base solution for the urban board (consumption, cost, development effort).

Now, we agree that NO2 sensors are important for urban pollution monitoring, and we won’t be left stranded without it. For that reason, a more stable solution was implemented in the Gas Pro Sensor Board, using Electrochemical Sensors from Alphasense Ltd during the iScape project. The solution implements not only NO2, but also CO and O3. The links above provide all the information about this board and the algorithm behind them. A single cell solution is also under development, similar to that ISB of Alphasense.
In terms of availability, there is no fixed date yet since the project that allows us to develop this is still going on, and we are in the final phases of the evaluation of these sensors.

Let us know if this helps.



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Dear Oscar

Yes thanks. As I am sure lots of people are telling you how Nitrogen oxides are so important, so a option ASAP would be great. As the Gas pro board has already been successfully deployed can that not be made available now?

Many thanks


Dear Andy,

Yes indeed, we are aware of the importance of NOx, as well as the difficulty to measure them. After some iterations, we learnt that Metal Oxyde sensors are not there yet, due to their difficulty to not be affected by temperature, humidity, Ozone, or many other things.

One of the reasons that this board is not released yet is that the post-processing required for the calculation of the pollutant concentration cannot be performed inside the Smart Citizen Kit and has to be calculated in a bigger machine a posteriori, i.e. the Platform. Since this processing is still under validation, we would not like to release the hardware yet. You could say it’s half baked.

In the meantime, what I can give you is some information about the calculation process, should you be interested about it, and some reference to devices that have been deployed for quite a while in the UK, related to your question here:

Finally, another thing you could do, in case these NO2 measurements are somehow urgent and cannot wait, is to prepare a solution including an I2C ADC like this from Adafruit and the ISB from Alphasense with a 4-electrode cell for NO2. This could be connected to the auxiliary port from the SCK and log the data, as seen here. This could be supported soon in a future version of the firmware, but it’s currently not implemented.

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Is there any update on Nitrogen oxides mesurement with the Smart Citizen Kit V2 ?

Based on the Gas Pro Sensor Board documentation page and the last answer on this thread I understand that we can connect the Alphasense NO2-B43F Electro chemical sensor on the firmware and start experiment NO2 mesurement ? Is it right ?

If it is the case could you please share some Smart Citizen Sensors ID in order to see what are the mesuremet results ?

The Alphasense NO2-B43F seems expensive : 280 euros ex-VAT. If this is the real price, is it possible to order customize smart citizen kit which are only dedicated to NO2 mesurement in order to lower the costs ?


We’re currently working towards a commercial release of the Smart Citizen Station. However, we are moving slowly because we are involved in many projects at the same time.

You can read more about our latest developments on the NO2 calibration in the report below:

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On a side note: the NO2-B43F is one of the 4-electrode electrochemical sensors by alphasense, but they also have more options. One cheaper options is the smaller NO2-A43F, with a smaller board. The idea of having the bigger option in the Smart Citizen Station, quoting the manufacturer, is because more electrolite (as it’s bigger) gives more stability to the readings temperature-wise, but the NO2-A43F is also a good option and probably surely a cheaper one, specially if contacting alphasense for more than one unit. The principle would be the same, auxiliary connector to an ADC hooked into the ISB as mentioned here:

Connecting Alphasense sensors to SCK2.1


Hi all,

regarding the inclusion of a NO2 sensor in the SmartCitizen kit (or either iScape), couple of further questions:

1- May we have any update of the status of iScape and its commercial launch?

2- In case iScape is not ready (or not planned yet) to be launch: Is there any kind of repository to connect the Seeed NO2 sensor to the smartcitizen 2.1 kit? Specifically, I am referring to Grove - Multichannel Gas Sensor v2



1- May we have any update of the status of iScape and its commercial launch?

The stations are available for commercial purchase directly by Fablab BCN. You can drop us an email at and we can discuss there your needs.

2- In case iScape is not ready (or not planned yet) to be launch: Is there any kind of repository to connect the Seeed NO2 sensor to the smartcitizen 2.1 kit? Specifically, I am referring to Grove - Multichannel Gas Sensor v2

The Grove Multichannel Gas sensor V2 is not supported atm. We measure NO2 using the Alphasense NO2 sensors with an ADC (we call it Analog sensor board). Two options here:

  • Either you can use the alphasense sensor (expensive, but good results)
  • Either we work on the implementation of that, but currently we are overflown with work. In this case, we could support remotely on the implementation if you feel confortable. Maybe it’s not too tricky as there’s already available libraries

Let us know!