Fungal emissions from air conditioning cooling coils

The fin-and-tube heat exchangers from air conditioning (AC) units are known locations of microbial growth within the built environment. Prior studies have documented the presence of potentially harmful fungal taxa on AC coils and noted the association of AC use and elevated respiratory symptoms in building occupants. This study aims to determine the rate at which fungi can be aerosolized from AC coils during normal operation. We investigated five AC units in commercial buildings in Southern CT, USA. At the end of the cooling season, we measured size-resolved aerosol concentrations (total, biological, fungal) upstream and downstream of the coils and applied ecological analysis to determine if fungal taxa on coil surfaces were emitted into downstream air. Coils were net sinks for a broad range of total aerosol sizes (0.4 to 20 μm). However, three of the five units were net emitters of bioaerosols with average emission rates of 5.6 × 10 7 to 7.2 × 10 7 biological particles hr -1 and 1.1 × 10 4 to 6.6 × 10 5 fungal spore equivalents hr -1 . Considering only measurements indicating the units as net sources, these AC units contributed approximately 34% of biological particle and 72% of airborne fungi in the downstream air. The two net sink coils were characterized by the presence of Leotiomycetes fungi , while the emitting coils had high abundance of Cladosporium , Penicillium, Aspergillus, Stachybotrys and Malassezia fungi. While most particles were found to deposit onto these coils, there is evidence that they can become net emitters of bioaerosols into air supplied indoors. • AC Coils were net sinks for a broad range of total aerosols in the upstream air. • 60% of the investigated AC units were net emitters of bioaerosols and fungi. • The non-emitting coils were characterized by Leotiomycetes and an elevated cooling load. • The emitting coil surfaces were abundant in Cladosporium , Penicillium, Aspergillus.