New Delhi, Nov 10 (ANI): As the pollution in Delhi-NCR reached an alarming level, residents prefer to invest in devices such as air purifiers to curb the level of pollutants indoor. In order to protect your lungs from inhaling the deteriorating air, here are few things you need to keep in mind before buying an air purifier Room Size: Before buying an air purifier you should keep in mind the room size. There are several air purifiers available in the market from compact to massive ones. Buy air purifier which is design to purify the air in a slightly larger space than the actual room size. Filter type: The air purifier’s filter must be equipped to filter things like pollen, dust, smoke, odour and other harmful pollutants. There are four types of filter available in the market: HEPA (High Efficiency Particulate Air), charged media, antibacterial and germicidal, and electrostatic precipitator. Air change rate: Air change rate indicates how many times the air purifier has cleaned the complete room’s air during an hour. CADR rating: Clean Air Delivery Rate calculates how many cubic feet of air the purifier can filter in one minute. Higher the CADR number, better will be the air filtration. If your operating space is large, then go for air purifier that has higher CADR rating. Portability and weight: The portability and weight of the air purifier should be kept in mind while buying one because a small air purifier may have the capability of cleaning a big room. Filter replacement and customer service: Before buying an air purifier one must also keep in mind the filter replacement and customer care aspects. The filter of air purifier needs to be changed periodically so, check for post-sale service offered by the company.