Modern particulate filters are pleated: you take a thin filter material that is effective at blocking particles but hard to get air through, and then fold a bun

Modern particulate filters are pleated: you take a thin filter material that is effective at blocking particles but hard to get air through, and then fold a bunch of it up in a small space to increase the surface area and decrease the pressure drop required for air to flow through it. If you don't have a suitably thin material or don't have this technique, increasing the surface area by, say, making it into a big cone would probably also work. The miasma theory isn't quite right, but it could conceivably have provided a half decent rubric for designing a working particle filter: at least some unpleasant smells are carried by particles. (Burning incense inside the mask is an example of where this theory might lead you off course.)