Air purifiers don't affect the level of oxygen in the room in any way. Your air purifier is recirculating the air already in the room and cleaning it by passing it through a filter where microscopic, solid particles are removed. It is neither removing nor adding additional oxygen into the space. Air purifiers are also not the same as freestanding air conditioners, though the increased airflow from an air purifier may make the air in your home appreciably cooler.