[Influence of Dust Events on the Concentration and Size Distribution of Microorganisms in Bioaerosols]

In order to study the influence of dust events on the airborne microbes in atmospheric bioaerosols, bioaerosol samples were continuously collected from March to April 2015 during two dust events using size-fractionated bioaerosol samplers in Lanzhou and Qingdao. The concentration of airborne microbes were measured using an epifluorescence microscope after staining with DAPI (4',6-diamidino-2-phenylindole). The results showed that the concentration of airborne microbes increased significantly during the period of dust (P<0.05). The average concentrations of airborne microbes on sunny days were 5.61×10⁵ cells·m^-3 and 2.08×10⁵ cells·m^-3 in Lanzhou and Qingdao, respectively, whereas the mean concentrations on dusty days were 14.8 times and 6.42 times those on sunny days, respectively. The concentration of airborne microbes presented a bimodal size distribution on sunny days in Lanzhou and Qingdao, with a peak at>7.0 μm and the lowest values ranging from 4.7 μm to 7.0 μm. However, the second peak appeared at 3.3-4.7 μm and 1.1-2.1 μm in Lanzhou and Qingdao, respectively. The size distribution of airborne microbes changed during the dust period. The size distribution of microbes still presented a bimodal distribution in Lanzhou; however, one peak shifted from>7.0 μm to 1.1-2.1 μm. The size distribution in Qingdao changed from a bimodal distribution to a skewed distribution with the predominant fraction in coarse mode. The background values of microbial load in PM₁₀ before the dust were 2224 cells·μg^-1 and 1550 cells·μg^-1 in Lanzhou and Qingdao, respectively, and the highest value of such increased significantly to 26442 cells·μg^-1 and 10250 cells·μg^-1 during the dust events, respectively. This demonstrated that the high concentration of microbes in the dust events resulted not only from increased atmospheric particles but also from dust source and transportation path along with long-range transported dust particles.