New Delhi, Nov. 4 -- Delhi-NCR's AQI has already crossed 350, placing the region in the very poor category and making outdoor exposure a serious concern. Keeping windows shut may limit some outside pollution from entering, but indoor air can also contain fine particles, dust, smoke and other pollutants. An air purifier can help reduce certain airborne particles in an enclosed room, provided its capacity matches the space and its filters are maintained on time. The choice, however, is not as simple as picking a familiar brand. Room coverage, filtration technology, clean air delivery rate, noise levels and replacement-filter costs all deserve attention. Here in this article, we'll bring together seven options from Dyson, Xiaomi, Qubo, Honey...