I've been playing with Arduino and Grove for a while now and finally got my hands on some gas sensors that can detect carbon monoxide, alcohol, acetone, formaldehyde and other chemicals. If you're not familiar with Grove it essentially modularises components so you can focus on rapid design rather than wiring.
Anyway, I assembled the kit and ran a variant of this code with some added functionality that flashed LEDs when pollutants were detected.
After a few false starts, I finally got it working and wandered the house.
"Sensor_value:55, Air fresh"
I hovered it over an open bottle of glass cleaner: