The standardised method (the Protocol) for the biovalidation of air purifiers (a.k.a. air scrubbers) developed for NHS Supply Chain is described. The Protocol determines the clearance rate of aerosolized Micrococcus luteus in a closed room-sized chamber achieved by the air scrubber under test. Aerosolization of the bacterium suspension is by venturi nebuliser. Air sampling is by a Coriolis air-to-liquid impinger. Collected samples are spiral plated on to agar plates. After incubation, colony development is quantified as the number of colony-forming units using a dedicated image processor. Microbiology methodology is accredited to ISO/IEC 17025:2017. Clearance rates are inferred from data represented by a first order exponential decay model. Read the full protocol by following the link below.