A long time has passed since I wrote Part 1, and I presented the results for NO2 and PM2.5 measurements between the low-cost sensors and the reference monitors. Due to the COVID-19 pandemic, laboratories were closed for 2 months so they couldn’t send me the results but since the 1st of June, I have the results in my hands.

These are the data they sent me. Two daily average values for the 31st of January and the 3rd of February. Data for the 1st and 2nd of February weren’t available for a validity reason.

I know it is ridiculous for an urban state reference station to give you just two values for four days. I am curious to learn what exactly they do with these values, what kind of studies (rolling my eyes now).

Unfortunately, I am unable to compare the PM2.5 low-cost sensors with the BAM results as I wanted, so the only thing I could do is to average the values from the low-cost sensors for the specific days and place them side by side. However, it won’t do it as it will create a huge confusion.

Conclusion

You start evaluating portable low-cost sensors, and you end up finding that the official city station is so outdated (accurate but outdated). This is the reason I am going to review an outdoor monitor (Clarity) that is designed specifically for cities that lack real-time PM2.5 monitoring, and it can offer a denser spatial coverage.

Regarding the Atmotube Pro and Flow 2, I will also compare them against the outdoor monitor in order to get a better idea about the PM2.5 monitoring capabilities.