Contribution of Primary Biological Aerosol Particles to airborne particulate matter in indoor and outdoor environments

Abstract

The atmospheric concentration of bioparticles was determined in some outdoor and indoor sites by using a commercial low-volume sampler and a detection method based on particle collection on polycarbonate filters, propidium iodide staining, observation by fluorescence microscopy and image analysis.Outdoor sampling was continuously carried out from May 2015 to October 2016 by cumulating monthly samples over individual filters. PBAPs contribution to PM10 concentration was in the range 0.7–13%. Seasonal differences were found in PBAPs concentration, shape and mass distribution. Higher concentrations were recorded during the warm period, when the bioparticles were more numerous, larger and more elongated.Simultaneous indoor and outdoor daily samples were collected during the spring of 2014 and 2017 in domestic environments. In indoor sites PBAPs were much higher in concentration than outdoors and showed a different visual appearance, with very wide polyhedral-shaped particles identifiable as skin flakes. Indoor/outdoor ratio (I/O) of PBAPs was in the range 6–16. Indoors, PBAPs contributed 21–77% to organic matter and 16–68% to PM10.When sampling into a sealed room, I/O was only 0.01 for individual bioparticles heavier than100 ng, while it was in the range 0.24–0.43 for PBAPs below 20 ng. This suggests that the infiltration factor of wide bioparticles was very low and that their concentration increase in indoor environments was due to indoor sources, namely the presence of human beings. Samplings carried out in different rooms of an apartment showed that most of the PBAPs mass was due to particles heavier than 100 ng, particularly in the bedroom.