An air purifier is a device designed to remove contaminants from the air in a room or an entire building. It works by filtering out pollutants such as dust, pollen, smoke, and pet dander, improving indoor air quality. Many air purifiers use HEPA filters, which can capture particles as small as 0.3 microns, making them effective for allergy sufferers. Some air purifiers also include additional features like activated carbon filters to reduce odors and UV light to kill bacteria and viruses. They are commonly used in homes, offices, and hospitals to create a healthier environment for occupants, especially those with respiratory issues or allergies.