Looking at the sensor from the bottom, you can see the two tabs/prongs that hold the outer case together.

There is a fine cable attaching the internal components of the PM sensor. Be careful not to disrupt/break it.

The internal housing will now be exposed. You can use the two tabs/prongs on this porting to remove that portion of the case.

Next, you can remove the 4 small screws holding the internal components to the outer shell.