Variations, seasonal shifts and ambient conditions affecting airborne microorganisms and particles at a southeastern Mediterranean site.

Airborne particles are known climate drivers whilst the impact of microorganisms is investigated with increasing interest. The particle number size distribution (0.012-10 µm), PM10 concentrations, bacterial communities and cultivable microorganisms (bacteria and fungi) were measured simultaneously throughout a yearly campaign at a suburban location at the city of Chania (Greece). Most of the bacteria identified belonged to Proteobacteria, Actinobacteriota, Cyanobacteria, and Firmicutes, with Sphingomonas having a dominant partition at the genus level. Statistically lower concentrations of all microorganisms and bacterial species richness during the warm season due to the direct impact of temperature and solar radiation suggested notable seasonality. On the other hand, statistically significant higher concentrations of particles <0.1 µm during the cold season was attributed to indirect seasonality with enrichment due to heating emissions. Analysis of wind direction data demonstrated that a land prevailing origin of air resulted in statistically higher microorganism concentrations, bacterial species richness and diversity, indicating the continental environment as a dominant contributor in shaping airborne microbial load (compared to a marine air origin). Likewise, statistically higher concentration of particles <0.1 µm were measured during a land prevailing air origin as a direct result of nanoparticle enrichment from anthropogenic activities. Long-range transport of both particles and biological components was evidenced by the increased concentrations of cultivable microorganisms (with a distinct contribution at sizes >1 µm), supermicron particles and bacterial species richness during Sahara dust events. Factorial analysis of the impact of 7 environmental parameters on bacterial communities profile has identified temperature, solar radiation, wind origin and Sahara dust as strong contributors. Increased correlations between airborne microorganisms and coarser particles (0.5-10 µm) suggested resuspension, especially during stronger winds and moderate ambient humidity, whereas, increased relative humidity during stagnant conditions acted as inhibitor for suspension.

Airborne particles and microorganisms in a dental clinic: Variability of indoor concentrations, impact of dental procedures, and personal exposure during everyday practice.

This study presents for the first time comprehensive measurements of the particle number size distribution (10 nm to 10 µm) together with next-generation sequencing analysis of airborne bacteria inside a dental clinic. A substantial enrichment of the indoor environment with new particles in all size classes was identified by both activities to background and indoor/outdoor (I/O) ratios. Grinding and drilling were the principal dental activities to produce new particles in the air, closely followed by polishing. Illumina MiSeq sequencing of 16S rRNA of bioaerosol collected indoors revealed the presence of 86 bacterial genera, 26 of them previously characterized as potential human pathogens. Bacterial species richness and concentration determined both by qPCR, and culture-dependent analysis were significantly higher in the treatment room. Bacterial load of the treatment room impacted in the nearby waiting room where no dental procedures took place. I/O ratio of bacterial concentration in the treatment room followed the fluctuation of I/O ratio of airborne particles in the biology-relevant size classes of 1-2.5, 2.5-5, and 5-10 µm. Exposure analysis revealed increased inhaled number of particles and microorganisms during dental procedures. These findings provide a detailed insight on airborne particles of both biotic and abiotic origin in a dental clinic.

Inorganic and carbonaceous components in indoor/outdoor particulate matter in two residential houses in Oslo, Norway.

A detailed analysis of indoor/outdoor physicochemical aerosol properties has been performed. Aerosol measurements were taken at two dwellings, one in the city center and the other in the suburbs of the Oslo metropolitan area, during summer/fall and winter/spring periods of 2002-2003. In this paper, emphasis is placed on the chemical characteristics (water-soluble ions and carbonaceous components) of fine (PM2.5) and coarse (PM2.5-10) particles and their indoor/outdoor relationship. Results demonstrate that the carbonaceous species were dominant in all fractions of the PM10 particles (cut off size: 0.09-11.31 microm) during all measurement periods, except winter 2003, when increased concentrations of water-soluble inorganic ions were predominant because of sea salt transport. The concentration of organic carbon was higher in the fine and coarse PM10 fractions indoors, whereas elemental carbon was higher indoors only in the coarse fraction. In regards to the carbonaceous species, local traffic and secondary organic aerosol formation were, probably, the main sources outdoors, whereas indoors combustion activities such as preparation of food, burning of candles, and cigarette smoking were the main sources. In contrast, the concentrations of water-soluble inorganic ions were higher outdoors than indoors. The variability of water-soluble inorganic ion concentrations outdoors was related to changes in emissions from local anthropogenic sources, long-range transport of particles, sea salt emissions, and resuspension of roadside and soil dusts. In the indoor environment the infiltration of the outdoor air indoors was the major source of inorganic ions.

Microorganisms in bioaerosol emissions from wastewater treatment plants during summer at a Mediterranean site.

Measurements were conducted at a Mediterranean site (latitude 35 degrees 31' north and longitude 24 degrees 03' east) during summer, to study the concentration of microorganisms emitted from a wastewater treatment plant under intensive solar radiation (520-840 W/m2) and at elevated air temperatures (25-31 degrees C). Air samples were taken with the Air Sampler MAS 100 (Merck) at each stage of an activated-sludge wastewater treatment (pretreatment, primary settling tanks, aeration tanks, secondary settling tanks, chlorination, and sludge processors). Cultivation methods based on the viable counts of mesophilic heterotrophic bacteria, as well as of indicator microorganisms of faecal contamination (total and faecal coliforms and enterococci), and fungi were performed. During air sampling, temperature, solar radiation, relative humidity and wind speed were measured. The highest concentrations of airborne microorganisms were observed at the aerated grit removal of wastewater at the pretreatment stage. A gradual decrease of bioaerosol emissions was observed during the advanced wastewater treatment from the pretreatment to the primary, secondary and tertiary treatment (97.4% decrease of mesophilic heterotrophic bacteria, and 100% decrease of total coliforms, faecal coliforms and enterococci), 95.8% decrease of fungi. The concentration of the airborne microorganisms at the secondary and tertiary treatment of the wastewater was lower than in the outdoor control. At the same time, the reduction of the microbial load at the waste sludge processors was 19.7% for the mesophilic heterotrophic bacteria, 99.4% for the total coliforms, and 100% for the faecal coliforms and the enterococci, 84.2% for the fungi. The current study concludes that the intensive solar radiation, together with high ambient temperatures, as well as optimal wastewater treatment are the most important factors for low numbers of microbes in the air.