Remote sensing of vehicle emissions consists of analyzing the emissions of a vehicle passing by using a light source and a light detector (generally in the IR and UV range) to check if the car is compliant to the current legislation against pollution.
This works because each pollution element absorbs the light at a different frequency.
As far as I know there are the existing commercial devices that can do this are:
These devices consists basically in two parts to be put on the opposite sides of the street: an emitter (or emitter/detector) and a detector (or a mirror to bounce the light back to the emitter/detector device).
These devices are very expensive because they are ready-to-use and includes a graphical interface so that almost anyone can use them and I think they implement all the algorithms to get the concentration but I am not interested in them. So I am looking if it is possible to build something (even less precise) by myself starting from lower-level elements.
Does anyone know if there exist light emitters/detectors sensors to analyze gas concentration(s) for this task where the emitter and detector are separate and that can work with a relatively long distance (3-4 meters) and whose output can be acquired/sampled by an embedded computer?
The optical gas sensors I have seen are generally on single-board while others are for proximity/obstacle detections so that the frequency they use is not suitable for such applications.