What is the best air purifier for cat litter smell?

For cat litter smell, the best air purifier is usually one with a large activated carbon filter plus a true HEPA filter.

• Activated carbon is the key feature for odor control, because HEPA alone mainly captures dust and dander, not gases such as ammonia.
• Look for a model with a thick carbon bed or substantial carbon pellet filter rather than a thin carbon-coated sheet, since more carbon generally gives better odor control and longer filter life.
• A true HEPA filter is still useful for trapping litter dust and airborne allergens.

For placement, put the purifier near the litter area with enough space for good airflow, but not directly on top of the box.

An air purifier works best as a supplement: scooping daily and changing litter regularly are still essential for controlling odor.