Mobile air cleaners are gaining popularity since they can be effective tools for improving the 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 homogenous mixing of the test aerosol. In contrast, real use scenarios might considerably differ from these conditions. This can involve adverse consequences since a less homogenous distribution of the cleaned air might lead to spatial differences of the CADR and thus to a lower overall efficacy of the air cleaner.
Therefore, in this study the spatial variance of the local cleaning efficacy at several positions within a furnished and in-use office was investigated for four different scenarios, in each of which the air cleaner was located at a different position. 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 measuring positions throughout the room, hinting towards a homogeneous distribution of the cleaned air. Variations of the positioning of the air cleaner in the room resulted only in minor differences, except for an intentionally chosen unfavourable position 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 CADR determined according to the Chinese standard GB/T 18801-2015 in a standardized test chamber, which is presumably mainly attributed to the different size distributions of the realistic and the standard test aerosol.