The emission of alkali and heavy metals in combustion processes is an important contributor to environmental load. However, little is known of the mechanism by which gas-to-particle conversion occurs during cooling and dilution with the atmosphere at the exit of stacks. In the present work, particles generated from model exhaust gases derived from NaCl and CdCl2 were investigated experimentally in the laboratory. An on-line, gas-phase measurement system showed that the mean diameters of aerosol particles in single-metal evaporation of NaCl and CdCl2 were 35 and 30 nm, respectively, when the dilution ratio of the model gas was 1:20. However, the value was 50 nm in two-metal co-evaporation of NaCl with CdCl2 at the same dilution ratio. FE-SEM images of aerosol particles collected with a quartz fiber filter in the two-metal system showed a morphology similar to that of NaCl. It is thus concluded that Cd-containing vapors nucleate at and grow on the surface of NaCl particles. These results may be informative for predicting phenomena related to gas-to-particle conversion at the exit of stationary emission sources, from which such condensed particles are suspected to be released into the atmosphere.
In order to understand the sulfur dry deposition on forests in East Asia, a simplified methodology on deposition velocity estimation was applied to estimate the dry deposition. The simplified method, originally based on the method of Matsuda (2008), can estimate the deposition velocity from wind speed, temperature and relative humidity with hourly or 6-hourly resolutions. The deposition velocities estimated by the simplified method were in good agreement with those by the original method in 2-week average comparison at 5 sites in Japan and 1 site in Thailand, and they are preferably compared with the recent observations. The applications of the simplified method in 27 sites in East Asia from 2003 to 2008 indicated that both SO2 and particulate SO42- deposition velocities on forest surface were higher around Japan and lower around Mongolia and tropical area. The distribution was similar to that of wind speed. Dry deposition of particulate nss-SO42- occupied about 30% of total sulfur dry deposition in the regional average. The ratios were relatively high in remote areas of Japan, because of lower concentrations of SO2 and higher concentrations of particulate nss-SO42-. Ratios of total dry deposition to wet deposition were high at a high latitude and low at a low latitude because of low wind speed and large precipitation at a low latitude.
Moment Dynamics Equations of the Modal Aerosol Dynamics was extended to simulate the Brownian coagulation of multimodal aerosol covering full size ranges and arbitrary fractal dimensions. The model was referred to as Modal Aerosol Dynamics model for multiple Modes and fractal Shapes (MADMS). However, the modal methods including MADMS had a critical limitation in application that a mode is always described by a single size distribution function. In order to describe a complex shape of size distribution, the modes of MADMS are discretized into bins in size dimension. The new approach is referred to as Modal Bin Hybrid Model (MBHM). As a performance evaluation of MBHM, one box model calculations were performed to simulate the rapid, simultaneous and non-equilibrium evolution processes of atmospheric aerosols through new particle formation, condensation and coagulation from 1 nm to sub-micron meter ranges.
Polycyclic aromatic hydrocarbons (PAHs) in aerosols were observed at Cape Hedo (26.87°N, 128.25°E, 60 m above sea level), Okinawa, where there is no influence of local anthropogenic emission, in order to investigate long-range transport of pollution from East Asia. The observations were conducted every season in 2010. The average concentrations of total suspended particles (TSP) in spring (n = 22), summer (n = 5), autumn (n = 4), and winter (n = 4) were 54.0 ± 26.4 μg m-3, 24.9 ± 7.28 μg m-3, 47.6 ± 34.0 μg m-3, and 60.3 ± 34.1 μg m-3, respectively. The average total PAHs (15 species) were 474 ± 671 pg m-3, 14.5 ± 2.45 pg m-3, 220 ± 239 pg m-3, and 2443 ± 2466 pg m-3, respectively. Both TSP and total PAHs showed the maximum during the spring, and showed the minimum during the summer. Backward trajectories and cluster processing indicated that the concentrations of pollutants depend on origins of air masses. The ratio of isomers of PAHs showed that the origins of winter air masses were coal and biomass combustion, while those in spring and autumn were mainly petroleum combustion.
Observations of atmospheric aerosols were carried out at Maebashi and Mt Akagi located in the inland Kanto plain. Fine and coarse particles were collected using a low-volume air sampler, and organic carbon (OC), water-soluble organic carbon (WSOC), elemental carbon and ionic components were measured. The highest concentration of fine particles was observed in spring, and nitrate and sulfate were the major components. Sulfate and OC were dominant in summer and fall. We found that ammonium sulfate was widely distributed in the inland Kanto plain while ammonium nitrate was localized in Maebashi. The seasonal variation of WSOC concentration rising from summer to fall was observed at Maebashi. The WSOC/OC ratio increased in summer, suggesting that organic aerosols were influenced by aging. We focused on water-soluble organic components in fine particles; dicarboxylic acids as tracers of photochemical reaction products, and levoglucosan as a tracer of biomass burning emission. The concentrations of total diacids in spring and summer were higher than in winter. WSOC concentration showed highly positive correlation with total diacids concentration in each season. Levoglucosan observed was considerably high in winter. We found that the secondary formation is the dominant source of organic aerosols, especially in the warm seasons, and that biomass burning is another important source of organic aerosol in winter.
Novel bipolar and unipolar charger where particles and high concentration ions are mixed quickly by ion flow and aerosol flow into the charging chamber without an external electric field are developed. The advantage of this method is 1) particle deposition by thermal motion and electrostatic dispersion is very low, and 2) particles are charged at a high efficiency. The new method employs a high-pressure corona ionizer for ion generator, because this ionizer can generate high concentration bipolar and unipolar ions applying an ac or a dc high voltage. It is found that the bipolar charger named as Mixing-type Bipolar Charger using Corona-discharge at High Pressure (MBCCHP) can attain the equilibrium charge distribution for 5-100 nm-particles. It is also found that the unipolar charger named as Small Mixing-type Unipolar Charger (SMUC) with chamber volume of 0.5 cm3 can achieve high extrinsic charging efficiency in the size range of 5-40 nm. Previously, the highest extrinsic charging efficiency for 5 nm was about 10%. However, the SMUC attained about 40% of extrinsic charging efficiency for 5 nm. From the results of diesel exhaust measurements of constant and transient driving, it is found that the MBCCHP and SMUC are very useful chargers in field measurements of diesel exhaust as well as in laboratory experiments.
This study focused on modification effects of soot-containing particles by aging and in-cloud scavenging processes. Morphological features and mixing states with water-soluble materials of soot-containing particles collected at two observation sites were analyzed by a transmission electron microscopy (TEM) with extraction of water-soluble materials. To elucidate the aging effects after their transport from megacities, we obtained aerosol samples for continental outflow at Cape Hedo, Okinawa in March 2008. Most soot-containing particles (0.2-0.7 μm) were mixed with water-soluble materials. Some soot-containing particles were found as clustered particles in multiple small (ca. 0.3 μm) spheroids. They were attributed to coagulation of solid spheroidal particles. At Mt. Tateyama (2300 m a.s.l.) in June 2007, cloud interstitial particles were measured using fog (>10 μm)-cut inlets. During fog condition under high precipitation (2-6 mm/hr), most of cloud interstitial particles (0.3-0.5 μm) were less- or non-hygroscopic particles. The results of TEM analysis suggested that most of the cloud interstitial particles were soot particles without water-soluble materials. These observation results suggested that morphological modification with coagulation process under high aerosol concentration and population change of the particles with in-cloud scavenging process are key processes controlling morphology and mixing states of soot-containing particles in the atmosphere. These changes of soot-containing particles must be considered when estimating direct radiation effect of aerosols from megacities and assessing climatic effects by long range transport of soot aerosols.
Asian dust which possibly carries microbial particles (KOSA bioaerosol) may impact ecosystems and human health in downwind environments. To confirm the atmospheric transport of microorganisms with KOSA, the KOSA bioaerosol preserved in seasonal snow cover on Mt. Tateyama in Toyama prefecture, Japan, was investigated by means of a culture-amendment technique targeting the halotolerant and oligotrophic bacteria which are known to be tolerant to atmospheric environmental stressors. The snow samples collected from the layers with and without KOSA particles in a 6.60 m deep-snow pit. The samples with KOSA particles indicated microbial growth in the culture media without dilution and with 10-1 dilution and with NaCl up to 10%, while the sample without KOSA particles showed no microbial growth. The phylogenetic analysis using 16S rRNA genes revealed that the members of the genus Bacillus were one of the major groups in the microbial structures. In particular, some species were identified as members of the B. subtilis group, which have been detected from the KOSA mineral particles collected from the atmosphere over KOSA arrival region (Suzu City). Presumably, the halotolerant and oligotrophic bacteria detected in this study were associated with the KOSA particles that descended to the snow cover on Mt. Tateyama.
The purpose of this study is to characterize airflow fluctuation, which occurs by the motion of traveling-type large crane, and to improve airflow environment in the clean stockers. Time-dependent change of airflow distribution and particle concentration were simulated using the multi-block simulation technique, and the factors of particle contamination on the surface of glass substrates in the stocker were studied. Clean stocker has rack zone and vehicle’s running zone. Rack area has FFUs (Fan Filter Units) on sidewall and ceiling, and they provide airflow distribution from rack area toward vehicle’s area. However, the traveling motion of the crane makes strong airflow turbulence, and it sometimes brings the invasion of particles from crane zone to rack zone. Countermeasures to the airflow intrusion were also studied. As the result of the study, speed control of the crane and separation of rack area were very effective to avoid the invasion of particles.