[zitoune]

- Are you driving the fan directly from an Arduino pin?

Ont he breadboard in the picture yes - but you can see a resistor at the base of a transistor 2N2222 to actually drive the fan. I have connected the fan directly to the arduino but I believe using the transistor is better.

"PM2.5, particulate matter with a diameter of 2.5 microns or less, has emerged as a pressing environmental concern, notably in China. Sharp Corp. has developed a PM2.5 sensor device, DN7C3CA006, which it claims is not only the smallest such device of its type but also the fastest, with a detection speed of 10 seconds"

- What is that "detection speed of 10 seconds" really means?

In the data sheet, it is mentioned to only power the fan intermittently in order to increase its life span.
A such, they do recommend to power it ON for at least 10 seconds every time - I believe below this time the measure might not be significant?
In my example it's powered for more than 30 sec to get the Vs reference.

--------

Another thing to note when measuring small particles: it does not really make sense to have "instantaneous" measures, but rather to take an average (like what you have implemented for the wind speed) over an hour.
Typical measures are given by national agencies over 1-hour or 3-hours. The most common for 2.5PPM is 1-hour. It would be easy to add in the program.

Regards.