You are right that this is a source problem rather than a filtration problem, and your instinct to check before buying is worth honouring.
Cooking is the largest indoor source of fine particles in most homes by a wide margin, and frying is the worst case - hot oil aerosolises. In a flat with decent outdoor air, your kitchen is the pollution.
Things that reduce it at the source, roughly in order of effect:
Use the back burners if your hood is over the hob. Capture is dramatically better at the back, because rising plumes at the front escape the capture area entirely. Free, and it is the largest single improvement available to most people.
Turn the hood on before you start and leave it on for fifteen minutes after. Your reading staying elevated for an hour is partly this, you are turning it off while the particles are still in the air.
Lids. Enormously effective and nobody wants to hear it.
Lower heat, less oil, and avoid taking oil to smoking. The smoke point is where the numbers go vertical.
Open a window while frying, even in winter, for ten minutes. Dilution beats filtration for something generated in the room.