Maybe, it depends on what you want to look for exactly, how prevalent it is, how distinguishable from natural stuff it is, how sensitive the detector is. I have been designing open-spectrometer with the goal of being useful for scientific work, where accuracy and precision are key. Sensitivity should be on-par with or better than commercially available devices in the $700-$4000 range, as the sensors used in such systems are identical to what I am using (I took inspiration from them), but I am using an higher-quality grating which is often a few thousand dollars extra upgrade. These gratings are more expensive, but less optical components (easier to build) and also aberration-corrected to produce a more linear spread of the wavelengths, with lower noise from 'higher orders' (aka 'ghost' images of the rainbow spectrum) falling onto the detector.

Can the spectrometer determine the makeup of the air? It seems like this would be valuable when looking at air quality or possibly the makeup of engine exhaust