Relationship between airborne microbial and particulate matter concentrations in the ambient air at a mediterranean site

The relationship between the viable airborne bacterial and fungal concentrations and the
respirable particulate matter with aerodynamic diameter less than 10 μm (PM10), 2.5 μm
(PM2.5), and 1 μm (PM1) in the ambient air was studied. An Andersen six stage viable particle
sampler and a MAS 100 sampler were used for microbial measurements. Duplicates of
samples were collected at each sampling period (20 campaigns in total) at a residential site in
the city of Chania (Crete, Greece) during April, May and June 2008.
Mean concentration of the total sum of the six size fractions was 79 + 41 CFU m-3 for
mesophilic heterotrophic bacteria, whereas for mesophilic fungi it was five times higher (395 +
338 CFU m-3). Particulate matter measurements at the same time period at the same site
revealed that the mean concentrations of PM10, PM2.5, and PM1 were 46 + 14, 35 + 14, and 28
+ 12 μg m-3, respectively, whereas the mean cumulate counts of PM1 particles was 5,059 +
1,973 particles cm-3. The mean arithmetic concentration of the size distribution of the airborne
fungi had a maximum at aerodynamic diameters between 2.1 and 3.3 μm. However, a
maximum was not observed for the mean arithmetic concentration of the size distribution of
the airborne heterotrophic bacteria. It was also observed that concentrations of airborne
bacteria and fungi outdoors were highly variable and do not correlate with the particle number
(PM1) or mass concentration of PM10, PM2.5 and PM1. Thereby, the R2-values in all
correlations were less than 0.3. However, the concentrations of airborne bacteria and fungi
were decreased with increasing mass concentrations of PM10, PM2.5, or PM1 while were
increased with increasing number concentration of PM1. In addition, the concentrations of
airborne bacteria were increased with increasing concentrations of airborne fungi. Finally, the
microbial or the particulate matter data did not correlate with meteorological parameters, such
as temperature, relative humidity, wind speed and UV radiation in ambient conditions.