 The PMSA003I is an I2C-enabled sensor that measures air quality by reporting the concentration of airborne particulate matter in three different size groupings. It's housed in a sturdy metal box, so of course we'll have to take a look inside and see how it works. First, a built-in fan draws in air at a fixed rate of speed. The air passes through an inner channel illuminated by a laser diode, and particles in the air cause light to scatter. An optical sensor positioned below the channel measures the deflected light. The relationship of these measurements to the known wavelength of the laser is then used to calculate particle sizes by a proprietary chip. The chip then sends results out over the I2C bus. Once again, proving that lasers are awesome.