Bacterial, fungal, and chemical emissions from air conditioning cooling coils

This study investigated the size-resolved emission rates of microbial aerosols emitted from commercial AC units and identified potential sources of bacterial and fungal growth and emissions of fungi within commercial HVAC systems. Commercial AC units in southern Connecticut were sampled and analyzed using spectrometry, quantitative polymerase chain reaction (qPCR) and next-generation DNA sequencing technologies. Results from capture on multistage impactors and from real-time bioaerosol fluorescence spectrometer measurements indicated that microbial emissions from AC units into buildings do occur, including emissions of hazardous fungi. As the concentrations of the bacteria and fungi upstream and downstream of the AC coils were not significantly different (P = 0.10 and P = 0.49, respectively), and the fungal ecology between upstream and downstream air determined by PCoA and ANOSIM was also not statistically significant (P = 0.6), this suggested that AC coil biofilms were likely not the source of microbial emission within the system. The filters and heating coils located upstream of AC coils appear to be the source of fungal growth and emissions within the system. These emissions include potentially hazardous fungi such as Aspergillus, Stachybotrys, and Penicillium. As the use and implementation of air conditioning expands, it is necessary to study the filters and heating coils present in these HVAC systems as well as explore microbial mitigation techniques to diminish the emission into buildings of microbes that may be negatively affecting human health.