Ippei Nagao

Contribution of particulate sulfate and organic carbon to cloud condensation nuclei in the marine atmosphere

To identify the source of cloud condensation nuclei(CCN) in the marine atmosphere, simultaneous measurements of aerosol chemical components and CCN concentration were made over more than a year at Hahajima, the Ogasawara Islands, located on the Northwest Pacific Ocean in the lee of Eastern Asian large pollution sources. Large loading of CCN in continental air mass and long-distance transportation to the remote ocean were confirmed. Non-seasalt sulfate and water soluble organic carbon were dominant in fine aerosols and their concentration revealed significant relationships with CCN concentration, suggesting that not only sulfate but also organic aerosols play a key role in CCN formation, especially in the background atmospheric condition.

Seasonal characteristics of organic and inorganic species and their size distributions in atmospheric aerosols over the northwest pacific ocean

Abstract In order to investigate the chemical properties of marine aerosols and the long-distance transport of continental aerosols to remote oceanic regions, simultaneous measurements of chemical compounds in atmospheric aerosols, cloud condensation nuclei (CCN) and associated species were conducted from December 1994 to January 1997 at Hahajima, the Ogasawara Islands, in the northwest Pacific Ocean, being located on the lee of the large east Asian polluted region. Clear change of air quality, caused by air mass alternation, are found. Concentrations of CCN and aerosol chemical species, such as non-sea-salt sulfate, nitrate, and oxalate, are low under the marine background conditions, whereas largely increased under the continentally affected conditions. It is ascertained that long-distance transport of these species to the remote ocean continues during half-year periods. Seasonal characteristics and size distributions of particulate organic acids, previously not well understood in earlier studies, are clarified. It is found that formate and acetate could have marine biogenic sources, mostly existing as coarse particles, whereas the oxalate was influenced by continental anthropogenic activity, displaying a relative predominance in the accumulation mode.

Differing Growth Responses of Major Phylogenetic Groups of Marine Bacteria to Natural Phytoplankton Blooms in the Western North Pacific Ocean

ABSTRACT Growth and productivity of phytoplankton substantially change organic matter characteristics, which affect bacterial abundance, productivity, and community structure in aquatic ecosystems. We analyzed bacterial community structures and measured activities inside and outside phytoplankton blooms in the western North Pacific Ocean by using bromodeoxyuridine immunocytochemistry and fluorescence in situ hybridization (BIC-FISH). Roseobacter/Rhodobacter, SAR11, Betaproteobacteria, Alteromonas, SAR86, and Bacteroidetes responded differently to changes in organic matter supply. Roseobacter/Rhodobacter bacteria remained widespread, active, and proliferating despite large fluctuations in organic matter and chlorophyll a (Chl-a) concentrations. The relative contribution of Bacteroidetes to total bacterial production was consistently high. Furthermore, we documented the unexpectedly large contribution of Alteromonas to total bacterial production in the bloom. Bacterial abundance, productivity, and growth potential (the proportion of growing cells in a population) were significantly correlated with Chl-a and particulate organic carbon concentrations. Canonical correspondence analysis showed that organic matter supply was critical for determining bacterial community structures. The growth potential of each bacterial group as a function of Chl-a concentration showed a bell-shaped distribution, indicating an optimal organic matter concentration to promote growth. The growth of Alteromonas and Betaproteobacteria was especially strongly correlated with organic matter supply. These data elucidate the distinctive ecological role of major bacterial taxa in organic matter cycling during open ocean phytoplankton blooms.

Sunrise ozone destruction found in the sub‐tropical marine boundary layer

A new mechanism of ozone loss is found in the sub-tropical marine boundary layer over the north Pacific. This ozone destruction occurs just after sunrise (hereafter Sunrise Ozone Destruction, SOD) and is commonly found throughout the year. SOD is a predominant ozone loss mechanism in winter, which takes place after sunrise in a few hours with 1∼2 ppbv of ozone depletion for 40∼50 ppbv of background ozone, while, in summer, SOD is weaker than in winter with small ozone depletion for 10∼20 ppbv of background ozone. In summer, daytime ozone destruction (hereafter, DOD) associated with UV photolysis and subsequent HOx reaction is more active. Since DOD is not active in early morning, SOD should be a new ozone loss mechanism. After demonstrating the observational findings, halogen chemistry associated with sea-salt aerosols is described as a possible mechanism.

Characteristics of dimethylsulfide, ozone, aerosols, and cloud condensation nuclei in air masses over the northwestern Pacific Ocean

Long-term measurements of several trace gases and aerosols were carried out from December 1994 to October 1996 at Ogasawara Hahajima Island over the northwestern Pacific Ocean. The continental impact on the concentrations of sulfur compounds, ozone (O3), and cloud condensation nuclei (CCN) was estimated on the basis of the classification of air mass into seven types by isentropic trajectory analysis. From May to October, the air mass originating from the central North Pacific Ocean is predominant and regarded as the clean marine air for the concentrations of sulfur compounds and CCN. From the results of the molar ratio of methane sulfonic acid to non-sea-salt sulfate (NSS) and the positive correlation between dimethylsulfide (DMS) and CCN in this air mass it can be concluded that DMS largely contributes to the production of NSS and CCN. On the other hand, continental and anthropogenic substances are preferably transported to the northwestern Pacific Ocean by the predominant continental air mass from November to March. The enhancement of concentrations by the outflow from the Asian continent are estimated by a factor of 2.8 for O3, 3.9 for SO2, 3.5 for CCN activated at 0.5% supersaturation (0.5% CCN), 4.7 for 1.0% CCN, and 5.5 for NSS. Moreover, the CCN supersaturation spectra are also affected by the continental substances resulting in factor 2 of enhancement of cloud droplet number concentration. The diurnal variations of DMS and O3 for each air mass show a pattern of daytime minimum and nighttime maximum, which are typically found in remote ocean, even though those amplitudes are different for each air mass. Consequently, it can be concluded that the influence of nitric oxides (NOx) for the daytime O3 production and nitrate (NO3) radical for the nighttime oxidation of DMS are small even in the continental air mass.

Relationship of NOX and NMHC to photochemical O3 production in a coastal and metropolitan areas of Japan

Atmospheric trace gases such as oxidants, nitrogen oxides (NOX) and non-methane hydrocarbons (NMHC) measured by the local Japanese government authorities were analyzed to elucidate the relationship between O3 and its precursors (NOX and NMHC) in metropolitan Nagoya and its coastal outskirts in Japan. Hourly data on oxidants, NOX and NMHC concentrations from 1991 to 2001 were used in order to clarify the seasonal variations, diurnal variations and photochemical potentials. Seasonal variation of O3 shows a general trend at mid-latitude in the northern hemisphere such as a maximum from late spring to summer and minimum in winter. However, coastal O3 concentrations are higher than urban ones even though the NOX and NMHC concentrations in the coastal areas are much lower than those in the urban areas. The data on NOX and NMHC concentrations are also used to describe O3 isopleth diagrams to elucidate the photochemical contributions to O3 production in these two areas. From the diagrams, O3 was found to be produced most effectively when the NOX/NMHC ratio is around 0.1 in both the urban and coastal areas. This value roughly corresponds to the numerical simulation results. Photochemical O3 production in the urban areas tends to be suppressed by the excess NOX concentrations. Photochemical O3 production in the coastal areas, on the other hand, is likely to be more active because the NOX/NMHC ratio has the most effective role in producing O3. This NOX/NMHC ratio shows a seasonal variation, which is close to the optimum ratio of O3 production from late spring to summer.

Elemental compositions of individual aerosol particles collected over the Southern Ocean: A case study

Abstract Marine aerosols have been sampled from the boundary layer over the Southern Ocean. By means of X-ray spectrometry, elemental compositions of individual particles have been studied. The data reveal the occurrence of two chemical processes over the Southern Ocean: (1) modification of sea salts by acidic materials, where Cl − is replaced by SO 4 2− and/or NO 3 − and (2) fractional recrystallization within evaporating seawater drops followed by shattering. The effects of these phenomena appear to be simultaneously enhanced when there is mass transfer from the free troposphere.