I have chosen to address the measurement of 2nd hand smoke in public.
This is a project that is targeted at public establishments that have outlawed smoking indoors. It is inexpensive to produce, and runs off of a small current source.
The body is a 3D printed piece that also functions as a shroud for the fan. On the top I have attached that project enclosure, that I have chosen to use without a lid, for easy cable management. I have cut a piece of particle board to attach the sensor to the back of the fan shroud. On the opening of the fan shroud I have zip stripped an 80 mm fan. The fan allows for better airflow to the sensor, thus it pulls in smoke easier
The code that is running on the Arduino can be found in the Git Hub repository. The code checks for smoke particles through the sensor. If smoke particles are detected the LED is lit.