Hi there, We have a Philips air purifier for sale, the model is AC4072. We bought it new in a department store for almost 3000 RMB at the beginning of 2014. The filters have been changed three months ago, so they can still be used for a certain period of time depending how often you switch it on of course. It DID change the air quality significantly in our room. It is a MUST in Beijing ( PM2.5 & other particals ). We would share with you the following article about this model, and that is reason why we choose Philips filter: