There has been interest in bioaerosols that have been linked to health hazards for humans, animals, and plants. Additionally, recently possible contributions of bioaerosols to atmospheric processes become a large concern from the view point of interaction between climate-weather and bioaerosol, especially the potential of micro organisms as ice nuclei. However knowledge on atmospheric bioaerosols is extremely poor due to the technical difficulty in measurement of bioaerosols in the atmosphere. Recently some investigators tried to collect atmospheric bioaerosols on high mountains and/or high tower to understand the transport processes, the environmental stress on micro biota in the atmosphere, the concentration and diversity of micro organisms in the atmosphere. Now the science of bioaerosols is world-widely accepted as large break-through in atmospheric science, aerosol science, environmental science, and others. The concentrations and diversity of bioaerosols in the atmosphere and the changes in their temporal-spatial are essential knowledge to clarify the long range transport of bioaerosols and the atmospheric processes affected by bioaerosols, and the environmental effects of micro organisms transported in long range. Balloon borne measurements were actively made in Kanazawa, Japan and Dunhuang, China in 2005-2009 suggesting that Kosa (Asian dust) particles were effective carriers of micro biota. Mixture states of Kosa and micro biota certainly suppress the environmental stress such as ultra-violet solar radiation, dryness and low temperature. The papers in this special issue of EAROZORU KENKYU are mainly based on these balloon borne measurements, and the newest information is described. Considering that the westerly wind frequently transports lots of Kosa particles from arid and semi-arid regions in China and Mongolia to downwind including Japan, the effect of Kosa bioaerosol mixture on environment, weather and health is of large concern in downwind areas. The paper by Kohshima (this issue) describes interesting and valuable topics in order to discuss the effects of Kosa bioaerosols on environment.
Ground-based observation at a large distance from desert regions suggested the possibility of long-range transport of bioaerosols along with desert dust. To understand the transport process, observation of bioaerosols associated with dust particles over KOSA (Asian dust) source areas is essential. In this paper, we introduce the observations of bioaerosols, which had been recently carried out at a desert site, Dunhuang in northwest China, using a tethered balloon. The tethered balloon served to lift instruments from the ground to about 1,200 m. Bioaerosol samples were collected at an altitude of 800 m above the ground. Particulate matters in the samples were analyzed individually with a fluorescent microscope and a scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX). According to the fluorescence microscopic observation with DAPI solution which stains DNA in samples, approximately 10 % of water-insoluble particles at 800 m showed strong fluorescent signals under UV irradiation, indicating the presence of microorganisms. The SEM-EDX analysis revealed that most of the fluorescent particles stained by DAPI were attached on mineral particles, indicating the significance of mineral dust as a carrier of microorganisms. In addition, these results show that coupling tethered-balloon observation with individual particle analysis is an effective approach to study the diffusion of mineral particles with bioaerosols in the boundary layer.
In order to study KOSA (Yellow dust) bioaerosols over a deposit region, we carried out direct samplings, separated culture, and identifications of KOSA bioaerosols over Noto peninsula, Suzu City in Ishikawa prefecture. KOSA bioaerosols were collected at a height of 400 m using a tethered balloon and bioaerosol sampler on May 7, 2008. After they were cultivated using a Nutrient agar, blood agar, potato dextrose agar, and Sabourand dextrose agar, 8 strains of isolates were obtained. The results of a homology search by 16S rDNA and 18S rDNA sequences of isolates in DNA databases (GenBank, DDBJ, and EMBL) revealed that the KOSA bioaerosols over KOSA deposit region contain Nocardiopsis sp., Bacillus sp., Streptomyces sp., and Bjercandera sp.
Bioaerosols are biological aerosols which contain microorganisms such as fungi, spores, bacteria, virus, and pollens. Bioaerosols should be considered an important factor which affects air quality, atmosphere of natural environment, and human health. At present, there are few reports for infectious risk management of bioaerosols (number concentration of microorganisms, organism species etc.), the role of bioaerosols in the ecosystem and the effect of bioaerosols on climate. In fact, it's difficult to investigate the total microorganisms in bioaerosols by culture-based method, because 99 % of bacteria in almost every environment on earth is unable to be detected and analyzed under laboratory conditions. As a method to overcome this bottleneck, a metagenomic analysis method for unculturable microorganisms in bioaerosols was described in this report.
The microbial communities transported by Asian desert dust (KOSA) events have attracted much attention as bioaerosols, because the transported microorganisms are thought to influence the downwind ecosystems in Japan. In particular, halotolerant bacteria which are known to be tolerant to atmospheric environmental stresses were investigated for clarifying the long-range transport of microorganisms by KOSA. Bioaerosol samples were collected at high altitudes within the KOSA source area (Dunhuang City, China) and the KOSA arrival area (Suzu City, Japan). The microorganisms in bioaerosol samples grew in media containing up to 15 % NaCl, suggesting that bacteria tolerant to high salinities would remain viable in the atmosphere. The PCR-DGGE (Denaturing gradient gel electrophoresis) analysis using 16S rRNA genes sequences revealed that the halobacterial communities in bioaerosol samples belonged to the members of the genera Bacillus and Staphylococcus and that some bacterial species belonging to Bacillus subtilis group were similar among the samples of both cities. Moreover, some sequences of B. subtilis group were found to be identical for the species collected at high altitudes and on the ground surfaces. This suggests that active mixing of the boundary layer transports viable halotolerant bacteria up to the free atmosphere at the KOSA source area, while down to the ground surface at the KOSA arrival areas.
Small sized organisms less than 2 mm, especially free-living microorganisms such as bacteria, fungi and algae tend to show world-wide distribution pattern. This suggests that many microorganisms travel to disperse long-distance in the air by wind. In fact, various microorganisms have been reported from the air at various altitudes in the troposphere, stratosphere and mesosphere (0–77 km a.s.l). Since dispersals to favorable habitats is important for microbes, it is possible that some microbes are adapted for long-distance dispersal in the air. For example, some bacteria and fungi living on leaf surface have been reported to produce ice-nucleation protains that function as condensation nuclei and ice nuclei. Hamilton and Lenton (1998) proposed a hypothesis that some microorganisms produce special substances that function as condensation nuclei and/or ice nuclei for cloud formation and migrate in the air safely and effectively in cloud droplets or in snowflakes. Recently, it has been reported that large part of the ice nuclei found in the new snow collected from various high-middle latitude areas were suggested to be microorganisms with ice nucleation protains. Therefore, microorganisms in the air could affect the cloud formation and precipitation in many regions of the world.
Biosol (microbe) sampling experiments have been conducted since the early 20 century. The relative difficulty in sampling using aircrafts, balloons or rockets limited the number of sampling experiments. However, spore forming microbes and Deinococci have been sampled by the limited number of experiments, both are known to be extremely resistant against extreme environments, such as UV and desiccation. Sampling devices are designed depending on the vehicle used for the sampling. The height dependence of the microbial density suggested the possible presence of microbes at the low earth orbit (400–500 km). The microbe sampling experiment at ISS (International Space Station) has been proposed in “Tanpopo” mission. We are going to use silica aerogel for capturing micro-particles including biosol, if the mission is finally accepted. The device for the sampling will be uplifted by the vehicle HTV and transferred to space through airlock and placed with robotic-arms. The device will be retrieved and carried back to the ground, where PCR analysis will be conducted after microscopic inspection of the biosol.
A new unipolar charger was developed, in which the electric field was impressed to separate unipolar ions from bipolar ions generated by alpha irradiation from radioactive source. The shape of the unipolar charger and the electric field impressed in it was optimized by numerical trial and error method. The evaluation of the charging rate of a design was evaluated by solving the spatial distribution of charged particles numerically as follows: the flow field and electric field was solved, and then, 1) the transport of ions and particles by convection, diffusion, and electrical migration, 2) aerosol charging and neutralization by combination of ions and particles, and 3) recombination of positive and negative ion, simultaneously. Field charging by ions and charged particles was excluded to reduce the computational costs. Charging rate, so-called extrinsic charging efficiency of the unipolar charger and conventional bipolar charger was investigated by tandem-DMA method directory. The charging rate of unipolar charger on the aerosol particles of 4 nm in diameter was twice as high as that of conventional bipolar charger, and more for larger aerosol particles.
The microphysical properties of dust over Eastern Asia are examined by using optical properties from the data collected by the space-borne lidar CALIOP onboard the satellite CALIPSO. The dust was frequently observed over northern China and northern India. The particle depolarization ratio (PDR) and the color ratio (CR) measured by the lidar respectively decreased and slightly increased from west to east above China. It is shown that the PDR decrease is not caused only by the change in shape distribution of the dust particles due to the shape-dependent falling velocity or the external mixturing of the dust with the secondary sulfate aerosols in accumulation mode, although it was suggested that the external mixturing of dust and sea salt particles could be the cause of the observed changes in PDR and CR. If soluble materials such as sulfate or sea salt are internally mixed with dust deliquesce in the atmosphere, the shape of the dust particles is more spherical, and their size is much larger. Therefore, this type of internal mixture should lead to the observed decrease in PDR and slight increase in CR. Moreover, since recent studies show that calcium-containing minerals react to form nitrate salts in polluted urban areas and these salts deliquesce under very dry conditions, this type of dust might also reduce PDR.