When sprinting/landing on floating bottom trapdoors, there are no particles. Trapdoors in all other configurations produce particles when sprinting/landing. Related bugs are MC-1691, as the game is likely attempting to show the particles of the air below, and MC-8820, which is similar.

What I expected to happen was...:
Particles to appear when sprinting on bottom trapdoors when there is no block underneath

What actually happened was...:
No particles appear

How to reproduce

1. Place down trapdoors of any type in the air (no blocks below them at all). Make sure they are on the bottom and not the top, and keep them closed.
2. Sprint or fall onto them, no particles appear (they do appear if the trapdoor is opened/on the top of the block)

Link to video demonstrating issue