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

Abstract

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.

Background Concentrations of Cultivable, Mesophilic Bacteria and Dust Particles in the Air in Urban, Rural and Mountain Regions

“…did not appear to be influenced by wind conditions, as the results of the bioaerosol measurements showed in a Greek city [57]. Other authors reported that there are definitely positive correlations between mesophilic bacterial concentrations and wind speeds of 1-3 m/s [55,56,70]. Perez (2012) observed a positive correlation (rho = 0.34) between fine and coarse particles during days with and without Saharan dust [71].…”

“…In this study, a negative correlation could be found between mesophilic bacterial concentrations and air humidity in the three geographical regions. Other investigations concluded that there are no correlations between mesophilic bacterial concentrations and air humidity [55][56][57][58]. Yao et al (2010) noted that the relatively large size of airborne particles allows for absorbance of more moisture from the air when the humidity increases.…”

“…Haas et al (2013) concluded that the total mesophilic bacterial concentrations decreased significantly with increasing ambient air temperatures whereas the air humidity has no influence on them [32]. Kolk et al (2009) and Raisi et al (2010) found no correlations between the two variables [35,56]. Other authors found correlations between concentrations of Staphylococcus sp.…”