Mobile air cleaners have been gaining popularity as potentially effective tools for improving indoor air quality. Usually, the efficacy of an air cleaner is quantified by determination of the clean air delivery rate (CADR) under strictly defined conditions within test chambers lacking furniture and featuring adequate and homogeneous mixing of the test aerosol. By contrast, real-world scenarios may considerably differ from these conditions, resulting in adverse consequences, as a less homogeneous distribution of the cleaned air may produce spatial differences in the CADR and lead to lower overall efficacy for the air cleaner.
Therefore, in this study, the spatial variance of a mobile air purifier’s cleaning efficacy across several positions in a furnished and in-use office room was investigated for four different scenarios, in each of which the air cleaner was placed in a different position inside the room. Ambient outdoor air was supplied as target aerosol by opening a window prior to the measurements, and the local CADR was calculated based on the decay rate of the lung-deposited surface area (LDSA) concentration. It was found that the relative decay of the LDSA concentration was almost identical for all of the measuring points throughout the room, hinting at a homogeneous distribution of the cleaned air. Varying the position of the air cleaner in the room resulted in only minor differences, except when the device was placed in an intentionally unfavourable location under a desk, which significantly reduced the cleaning efficacy. Despite the high spatial homogeneity, the CADR in the office room was significantly lower than the one determined according to the Chinese standard GB/T 18801-2015 in a standardized test chamber, which is presumably mainly attributable to the differing size distributions of the realistic and the standard test aerosol.