Air purifier

An air purification apparatus comprising:

• a flow channel extending between an inlet and an outlet;
• a pollutant removal structure and an air displacement apparatus in the flow channel;
• a branched sensor channel including:
• a first branch extending between an ambient air port and a further outlet in the flow channel between the inlet and the air displacement apparatus;
• and
• a second branch extending between the ambient air port and a further inlet in the flow channel between the air displacement apparatus and the outlet, the first branch and second branch sharing a branch section;
• at least one pollutant sensor in the shared branch section;
• a valve arrangements in the branched sensor channel adapted to exclusively disconnect the first branch from the flow channel in a first configuration and exclusively disconnect the second branch from the flow channel in a second configuration;
• and
• a controller adapted to control the valve arrangement;
• a processor communicatively coupled to the pollutant sensor, the processor being adapted to derive a pollutant concentration from sensor data provided by the pollutant sensor;
• wherein:
• the controller is adapted to:
• periodically switch the valve arrangement between the first configuration and the second configuration;
• derive a first pollutant concentration from sensor data provided by the pollutant sensor with the valve arrangement in the first configuration;
• derive a second pollutant concentration from sensor data provided by the pollutant sensor with the valve arrangement in the second configuration;
• and
• determine a pollutant removal efficiency of the pollutant removal structure from the derived first pollutant concentration and second pollutant concentration.