Air Quality over Europe

I noticed this article in the British Newspaper the Guardian yesterday Revealed: almost everyone in Europe is breathing toxic air | Air pollution | The Guardian
It suggests that over a vast area of Europe the air quality for PM2.5 is bad and yet for all of this year the Sensor Community monitors’ output has been low for most of the year. I really cannot understand why there is the difference in findings.

Yes. - I had also seen that article and the same question arose for me.

I remember a few days where much of Central Europe changed from its usual green to much higher readings. I assumed there were a combination of weather conditions that caused the PM2.5 levels to rise.

I also wonder about the calibration and accuracy of the sensors and software we are using. Is everything reading low giving an over optimistic picture?

If some sensors read high, some low - then this would average out…

Finally, while I subscribe to the Guardian, I suspect they are not immune to hyping data for sensationalising a story.

Somewhere is all of this lies the truth!

Here’s their methodology. I could not make much sense of it.

They cite Skopje in N. Macedonia as having the worst pollution in Europe. A quick look at the reasonably many sensors in Skopje reveals a better picture - most sesnors showing green.

Thank you for your reply. I agree that the truth is possibly somewhere in between.
I do have concerns currently that many of the sensor community sensors have been reading very low this year. For instance the sensors in my location in the U.K. are reading on average PM2.5 concentrations of 2-5ug/m^3 whereas last year the average value was around 8-10ug/m^3. Yes, weather patterns are different and perhaps this accounts for it. However, for the local TEOM, which measures PM10 values the concentration has not changed.
So there is a discrepancy which I haven’t resolved. I would be very happy if the low numbers were correct but as we still have the same traffic issues and NOx levels are high I am struggling with understanding why the PM2.5 values are so much lower this year.