Noctilucent (night-shining) cloud (NLC), which is often called polar mesospheric cloud (PMC) also, consists of water-ice particles with approximate radii of 1050nm, usually being formed in the polar summer mesopause region (8285km altitude). Ground-based visual, lidar, and radar observations and space missions as well as model/theoretical research have been carried out to clarify the NLC/PMC's climatology, characteristics, and formation mechanisms, extending the observations to mid latitudes in both hemispheres. The influence to global warming is controversial to some extent, while a significant correlation between 11-year solar cycle to NLC variation is suggested. Through the radar studies of polar summer mesosphere echo (PMSE), the NLC particles' important role has been recently stressed, leading to new dusty plasma sciences in the weakly-ionized upper atmosphere.
Polar stratospheric cloud (PSC) is considered to play an important role in the stratospheric ozone depletion through heterogeneous reaction on PSC particles and denitrification due to their gravitational sedimentation in the cold stratosphere. Recent extensive researches have drawn detailed picture of composition, nucleation and various properties of PSC particles, especially the effects on ozone destruction. This paper reviews the recent advances in our understanding of PSC particularly about their compositions and nucleation processes, and also discusses the relation of PSC activity with global environmental change.
Light absorbing carbonaceous particles in the atmosphere (i.e. black carbon and soot) have been of great interest from the view point of radiation budget and climate impact. Air quality including the carbonaceous particles is much different between Arctic and Antarctica. Because of large human activity in the Northern hemisphere (even in the Arctic Circle), many anthropogenic species are believed to be transported into the Arctic. In contrast, Antarctica is isolated from other continents and human activity. In this paper, we discuss the seasonal variation, the inter-annual variation, and the transport processes of absorbing carbonaceous particles in Arctic and Antarctica.
The direct and indirect radiative effects of aerosol particles and clouds have been identified as key uncertainties in the prediction of future global climate. In order to improve knowledge on aerosol and cloud properties, as well as their impact on climate in the Polar Regions, many observations have been carried out. This paper reviews the direct and indirect radiative forcing of tropospheric aerosols based on the field observations in the Polar Regions.
Light absorbing aerosols such as black carbon (BC) and mineral dust deposited on snow/ice surface reduce albedo and accelerate snow/ice melting. Through the radiative transfer calculation for the atmosphere-snow system, light absorbing aerosol concentration which reduces the snow albedo by 0.01 is approximately several to several tens ppbw for BC and 103 to 104 ppbw for the mineral dust. BC concentrations have been measured from in-situ snow samples since 1980s and from ice core even for a longer period. Greenland ice core records show high BC concentration during 1850-1950 due to industrial activities, and the BC measurements for in-situ snow samples indicate high values during 1980s in a wide area of the Arctic except Greenland. These high BC concentrations are the level which reduces the snow albedo by more than 0.01. Climate modeling studies including the effect of BC and dust in snow show that globally annual-mean radiative forcing due to BC (or dust) is less than 0.1W/m2, while their regional effect for a specific period is much higher. However, there are many issues to be dealt with in modeling studies as well as the measurement techniques of light absorbing aerosols in snow/ice.
The accumulation rate, aerosol flux, and air temperature fluctuation can be determined from the study of ice cores drilled through ice sheets and glaciers. The aerosol which gives climate and environmental information is accumulated on the surface of ice sheet. In order to elucidate the climate and environmental changes, it is necessary to find the changes in concentration, composition, and isotope ratio of impurities in accumulated particles after the deposition on the snow surface. This study revealed that the global climate and environmental changes have occurred on various time scales in the past million years. The characteristics of aerosol particles deposited on the Antarctic ice sheet are investigated. Furthermore, the history of solar activity and associated geomagnetic fields is clarified by analyzing the cosmogenic nuclides in ice cores. An interdisciplinary study on ice cores is also carried out to elucidate the evolution mechanisms of microorganisms in the ice cores.
A nasal swab sample, which is taken immediately after an inhalation accident of radioactive aerosols, shows provisional intake radioactivity. In the case of an alpha emitter, much time is needed to determine the intake radioactivity using bioassay. A nasal swab sample would give a better estimation for early dose. In this study, the most hazardous size to our health and how to estimate the exposure dose were considered from the viewpoint of emergency medicine. A computer code, LUDEP, was used to calculate the aerosol deposition in respiratory tract and the committed effective dose. Assuming that the radioactivity detected in a nasal swab sample was equal to the radioactivity deposited in the extrathoracic region 1 (ET1), the dose conversion factor (DCFnasal) was evaluated based on the relationship between the ET1-deposited radioactivity in Bq and the committed effective dose in mSv. The DCFnasal showed a clear dependency on the aerosol particle size. It was indicated that the reference aerosol with the size of 5μm for occupational exposure in the ICRP publication does not always give dose estimation in safer side. In the case of insoluble plutonium-239, the maximum value of 2.6mSv Bq-1 for DCFnasal was found at 0.02μm in a heavy exercise level of an adult. Therefore, the maximum value would be applied to first estimation of the dose for nuclear emergency medicine.
The purpose of this study is to investigate the sampling characteristics of molecular contaminants in indoor air undergoing corona discharge by measuring the adsorption under electric field. As electric discharge equipment for ionization, a corona-discharge-type ionizer (pulsed-DC type) was used. Chamber experiments were conducted at a voltage with different polarities applied to the collecting plate. Limonene was selected as a test VOC. Preliminary exposure experiments were carried out to determinate the appropriate exposure time and then the characteristics of surface adsorption was investigated. Furthermore, the concentration distribution of limonene in the chamber was measured to find the optimal condition for the subsequent experiments. The results showed that there exist significant differences in the adsorbed amount of test VOC depending on the polarity of collecting plate, suggesting that even nonpolar organic compounds behave like ions under the influence of corona discharge.
Perchlorate ion (ClO4-) has been recognized as a new environmental pollutant. The concern about ClO4- stems from the fact that it displaces iodide in the thyroid gland. Iodine-containing thyroid hormones are essential for proper neural development from the fetal stage through the first years of life. In this study, we determined the concentrations of ClO4- in aerosols collected at Cape Hedo Atmosphere Aerosol Monitoring Station of National Institute of Environmental Studies (NIES-CHAAMS) Okinawa Island, Japan. Aerosols were collected on quartz filters by using a high-volume air sampler. The ClO4- concentrations were determined by ion chromatography (ICS-2000, DIONEX). About 60% of the weekly-collected aerosols contained detectable level of ClO4-, and the highest ClO4- concentration for the samples collected at NIES-CHAAMS was 1.8ng m-3. Back trajectory analysis showed that ClO4- concentrations were higher when air mass came from Asian continent, suggesting that ClO4- found at NIES-CHAAMS was probably due to long-range transport from Asian continent.