Extract

This study aims i) to characterize the ratios of bioaerosol levels in a meeting room to outdoor
levels and ii) to investigate the impact of two factors, air‐conditioning and mechanical ventilation (ACMV)
operation status and human occupancy, on time‐resolved relationship between indoor and outdoor
bioaerosols. Using an ultraviolet‐light induced fluorescence (UV‐LIF) technique, we measured number
concentrations of total aerosol particulate matter (tPM) and fluorescent biological aerosol particles
(bioPM) (1.0‐3.0 μm and 3.0‐5.0 μm diameter) in an office and outdoors, sampling with 1‐min resolution.
The air‐conditioning and mechanical ventilation (ACMV) system equipped with high‐grade filters was
effective in controlling both tPM and bioPM indoors. As expected, removal efficiencies were found to be
size dependent. One human subject walking on the carpet was found to be a strong contributor to bioPM,
resulting in 2‐3 times higher concentration than that outdoors. Compared to the times when the room is
vacant, the biological proportion of total airborne particles increased by an order of magnitude during the
light walking period. Consequently, indoor‐to‐outdoor ratios depend on the ACMV operating conditions
and on human activities. This pilot study provides preliminary data concerning the bioPM levels in an
indoor environment equipped with an ACMV system. Ongoing investigations using this approach promise
to improve our understanding of the processes that influence indoor bioaerosol levels and the
effectiveness of control alternatives.

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