There are several types of air purifiers, including:

1. HEPA (High-Efficiency Particulate Air) filters: These remove very small particles, including allergens and bacteria, from the air.

2. Activated carbon filters: These remove odors and harmful chemicals by adsorbing them onto a surface.

3. UV-C light air purifiers: These use ultraviolet light to kill harmful microorganisms, including viruses and bacteria.

4. Ionizers: These release negatively charged ions into the air, which then bond with positively charged particles, making them heavier and easier to remove from the air.

When choosing an air purifier, it's important to consider factors such as the size of the room it will be used in, the type and level of pollutants you want to remove, and your budget. It's also recommended to replace filters regularly to maintain the purifier's efficiency.