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Two Japanese rice cultivars with different heat-tolerance, Hinohikari (sensitive) and Nikomaru (tolerant), were grown in pots inside open-top chambers and exposed to ambient CO2 (400 µmol mol-1) or elevated CO2 (550 µmol mol-1) from the beginning of the tillering stage to maturity. The study was conducted in Nagasaki, in the Kyushu region of Japan, where heat stress on rice has become increasingly evident. Although elevated CO2 significantly improved the net hotosynthesis and whole-plant growth of the cultivars, there were no significant effects on grain yield, which in turn reduced harvest index. In both cultivars, adverse effects occurred with elevated CO2, such as reductions in spikelet fertility and grain appearance quality, which are typical manifestations of heat stress in rice. During the flowering period, the air temperature was high that spikelet fertility was reduced even under ambient CO2 conditions for both cultivars. These results suggest that, under high-temperature conditions, elevated CO2 could induce or exacerbate the manifestations of heat stress in rice. Because transpiration rate in the flag leaf was significantly reduced by the exposure to elevated CO2, it is possible that elevated CO2 increased plant temperature via a reduction in transpiration during flowering period, although we did not detect significance of the increase in leaf and panicle temperature. To ensure a more confident conclusion, further studies focusing on the effects of elevated CO2 on the determinants of spikelet fertility and grain appearance quality with other cultivars in different year are required., Asian Journal of Atmospheric Environment, 16(3), art. no. 2022044; 2022

A horizontally pointing lidar is planned for deployment with other instruments in Fukushima, Japan, to continuously monitor and characterize the optical properties of radioactive aerosols and dust in an uninhabited area. Prior to installation, the performance of the lidar is tested at Chiba University. Data from the continuous operation of the lidar from August 2021 to February 2022 are analyzed for extinction and depolarization ratio. These are compared with the weather sensor and particulate matter (PM2.5) measurements to quantify the relationship between atmospheric conditions and optical properties of near-ground aerosols. The results show that lidar data’s extinction coefficient and depolarization ratio can have a quantifiable relationship with relative humidity (RH), absolute humidity, rain rate, wind speed, wind direction, and PM2.5 concentration. Analysis of the seven-month data shows that the optical properties of aerosol and dust depend on the combined effects of the weather parameters. An increase in RH or PM2.5 concentration does not imply an increase in radioactive aerosols. The average extinction coefficient and depolarization ratio of aerosols and dust originating from the land and ocean show different values and opposing trends which can aid in determining the occurrence of ground-based radioactive dust and aerosols. The information obtained from analyzing the interrelationship among lidar, weather parameters, and PM2.5 concentration is essential in assessing the occurrence of radioactive aerosols and characterizing local aerosol-weather relationships in a radioactive area. This result provides essential information in describing radioactive aerosols in Fukushima.

Filter-based offline analysis of atmospheric aerosol hygroscopicity coupled to composition analysis provides information complementary to that obtained from online analysis. However, its application itself and comparison to online analysis have remained limited to date. In this study, daily submicrometer aerosol particles (PM0.95, 50 % cutoff diameter: 0.95 μm) were collected onto quartz fiber filters in Okinawa Island, a receptor of East Asian outflow, in the autumn of 2015. The chemical composition of water-soluble matter (WSM) in PM0.95 and PM0.95 itself, and their respective hygroscopicities were characterized through the offline use of an aerosol mass spectrometer and a hygroscopicity tandem differential mobility analyzer. Thereafter, results were compared with those obtained from online analyses. Sulfate dominated the WSM mass (60 %), followed by water-soluble organic matter (WSOM, 20 %) and ammonium (13 %). WSOM accounted for most (93 %) of the mass of extracted organic matter (EOM) and the atomic O to C ratios (O : C) of WSOM and EOM were high (mean ± standard deviation were, respectively, 0.84 ± 0.08 and 0.79 ± 0.08), both of which indicate highly aged characteristics of the observed aerosol. The hygroscopic growth curves showed clear hysteresis for most samples. At 85 % RH, the calculated hygroscopicity parameter κ of the WSM (κWSM), WSOM, EOM, and PM0.95 (κPM0.95) were, respectively, 0.50 ± 0.03, 0.22 ± 0.12, 0.20 ± 0.11, and 0.47 ± 0.03. An analysis using the thermodynamic E-AIM model shows, on average, that inorganic salts and WSOM respectively contributed 88 % and 12 % of the κWSM (or κPM0.95). High similarities were found between offline and online analysis for chemical compositions that are related to particle hygroscopicity (the mass fractions and O : C of organics, and the degree of neutralization), and also for aerosol hygroscopicity. As possible factors governing the variation of κWSM, the influences of WSOM abundance and the neutralization of inorganic salts were assessed. At high RH (70–90 %), the hygroscopicity of WSM and PM0.95 was affected considerably by the presence of organic components; at low RH (20–50 %), the degree of neutralization could be important. This study not only characterized aerosol hygroscopicity at the receptor site of East Asian outflow, but also shows that the offline hygroscopicity analysis is an appropriate method, at least for aerosols of the studied type. The results encourage further applications to other environments and to more in-depth hygroscopicity analysis, in particular for organic fractions.

Secondary organic aerosol (SOA) formed from vehicle exhaust contributes substantially to the atmospheric particulate matter in urban air but there still remain uncertainties in the simulation of the SOA by air quality models. This omission is due partly to uncertainties about the differences in SOA formation between vehicle types, exhaust aftertreatment devices, and oxidation conditions in the air. In this work, smog chamber experiments were conducted to investigate SOA formation from diluted exhaust gases emitted by two light-duty gasoline vehicles and one passenger and one medium-duty diesel vehicles. Emissions were aged in the smog chamber under light (ultraviolet) and dark (with high O3) conditions. In these experiments, there were considerable emissions of elemental carbon and primary organic aerosol by a gasoline direct-injection vehicle and a diesel truck, but the corresponding emissions were relatively small from a gasoline vehicle with port fuel injection and a passenger diesel vehicle. However, significant amounts of SOA were produced from all four vehicles. Box model simulations indicated that OH exposure was higher and the ratio of NO to peroxy radicals (HO2 + RO2) was lower under dark conditions in the presence of high added O3 than under light conditions. The higher concentrations and yields of SOA under dark conditions than under light conditions could partly be explained by the lower NO/(HO2 + RO2) ratios under dark conditions. Simulations with a volatility basis-set model indicated that aromatic compounds were the dominant precursors of SOA from gasoline vehicles (64–84%), whereas unspeciated intermediate-volatility organic compounds (IVOC) were the dominant precursors for the production of SOA from diesel vehicles (75–87%). The observed O : C ratios were higher for gasoline SOA (0.7–0.8) than diesel SOA (0.3–0.4), and this difference was explained by the differences in their precursors. SOA formed under the light and dark conditions was similar in the dominant precursors and oxidants, as well as the O : C ratios, but different in the NO/(HO2 + RO2) ratios during the oxidation processes. Thus, we cannot conclude that SOA formed under the light and dark conditions has similar chemical composition, and their characteristics should be further examined in future studies.

HO 2 uptake kinetics onto ambient aerosols play pivotal roles in tropospheric chemistry but are not fully understood. Field measurements of aerosol chemical and physical properties should be linked to molecular-level kinetics; however, given that the HO 2 reactivity of ambient aerosols is low, traditional analytical techniques are unable to achieve this goal. We developed an online approach to precisely investigate the lower-limit values of (i) the HO 2 reactivities of ambient gases and aerosols and (ii) HO 2 uptake coefficients onto ambient aerosols ( γ ) during the 2019 Air QUAlity Study (AQUAS) in Yokohama, Japan. We identified the effects of individual chemical components of ambient aerosols on γ . The results were verified in laboratory studies on individual chemical components: transition metals play a key role in HO 2 uptake processes, and chemical components indirectly influence such processes (i.e., by altering aerosol surface properties or providing active sites), with smaller particles tending to yield higher γ values than larger particles owing to the limitation of gas-phase diffusion being smaller with micrometer particles and the distribution of depleting species such as transition metal ions being mostly distributed in accumulation mode of aerosol. The modeling of γ utilized transition metal chemistry derived by previous studies, further confirming our conclusion. However, owing to the high NO concentrations in Yokohama, peroxy radical loss onto submicron aerosols has a negligible impact on O 3 production rate and sensitivity regime.

· It is projected that atmospheric CO2 concentrations will increase because of industrial activities. Elevated CO2 reduces transpiration from leaves via stomatal closure, which increases plant temperature; therefore, higher levels of CO2 could adversely affect crop production via increasing plant temperature, particularly for plants that are susceptible to heat stress, such as rice (Oryza sativa). · Two Japanese rice cultivars with different heat-tolerance, Hinohikari and Nikomaru, were grown in pots inside open-top chambers and exposed to ambient CO2 (400 µmol mol–1) or elevated CO2 (550 µmol mol–1) from the beginning of the tillering stage to maturity. The study was conducted in Nagasaki, in the Kyushu region of Japan, where heat stress on rice has become increasingly evident.· During the flowering period, the air temperature was sufficiently high to induce heat stress effects in rice, such as low spikelet fertility, even under ambient CO2 conditions for both cultivars. Although elevated CO2 significantly improved the net photosynthesis and whole-plant growth of the cultivars, there were no significant effects on grain yield, which in turn reduced harvest index. In both cultivars, adverse effects on other processes occurred with elevated CO2, such as reductions in spikelet fertility and grain appearance quality, which are typical manifestations of heat stress in rice. The elevated CO2 treatment showed significant reductions in stomatal conductance and transpiration rate of flag leaves, which could increase plant temperature.· Under high-temperature condition, therefore, elevated CO2 could induce manifestations of heat stress in Japanese rice via reduction in transpiration due to stomatal closure.

he sphericity of particles must be considered when evaluating their effects on the climate and human health. Thus, to examine this property and its controlling factors, this study measured the scattering angular distributions of both thermodenuded and non-thermodenuded individual particles with a diameter of 500 nm in real time using a home-made polar nephelometer in Nagoya, Japan. Estimating the sphericities based on the depths of the local minima in the scattering angular distributions, we found the ambient aerosols to be external mixtures of at least two types of particles, one with relatively high and the other with relatively low sphericity. Although most of the particles exhibiting high sphericity were removed as they passed through the thermodenuder, approximately one-third of the fraction exhibiting low sphericity remained. During the daytime, the proportion of the low-sphericity particles decreased, whereas the average sphericity of the high-sphericity particles increased, which can be attributed to photochemical formation and/or aging processes. On days with extremely high relative humidity, the diurnal variation in the average sphericity displayed another peak during the early morning, which may have been due to the secondary formation of nitrate., Aerosol and Air Quality Research, 20(11), pp.2474-2484; 2020

The severe air pollution events continue to occur every year during late October and early November in Delhi, forcing air/land traffic disruptions and anxiety in the daily life of the citizens. We analyze the behaviors of the air pollution events in October and November 2019 that arose from the crop-residue burning as seen using remote sensing techniques. Transport pathways and the mean transit time from the fire hotspots are evaluated using the FLEXPART (FLEXible PARTicle dispersion model). Our results suggest that the polluted regions in Delhi are partly influenced by the crop-residue burning. The uncertainty of our evaluation can be attributable to insufficient information on emission sources because the biomass burning emission based on daily-basis fire radiative power (FRP) of Moderate-Resolution Imaging Spectroradiometry (MODIS) is significantly degraded by the existence of hazy clouds. In future, it is desirable to establish a dense measurement network between Punjab and Delhi for the early detection of the source signals of aerosol emissions and their transport in this region. The FLEXPART model simulation shows the transport of emission signals from Punjab to Delhi, which further expands toward the Bengal region within a span of two days.

A novel, practical observation system for measuring tropospheric carbon dioxide (CO2) concentrations using a non-dispersive infrared analyzer carried by a small helium-filled balloon (CO2 sonde) has been developed for the first time. Vertical profiles of atmospheric CO2 can be measured with a 240–400 m altitude resolution through regular onboard calibrations using two different CO2 standard gases. The standard deviations (1σ) of the measured mole fractions in the laboratory experiments using a vacuum chamber at a temperature of 298 K were approximately 0.6 ppm at 1010 hPa and 1.2 ppm at 250 hPa. Two CO2 vertical profile data obtained using the CO2 sondes, which were launched on 31 January and 3 February 2011 at Moriya, were compared with the chartered aircraft data on the same days and the commercial aircraft data obtained by the Comprehensive Observation Network for TRace gases by Airliner (COTRAIL) program on the same day (31 January) and 1 d before (2 February). The difference between the CO2 sonde data and these four sets of in situ aircraft data (over the range of each balloon altitude ±100 m) up to the altitude of 7 km was 0.6±1.2 ppm (average ±1σ). In field experiments, the CO2 sonde detected an increase in CO2 concentration in an urban area and a decrease in a forested area near the surface. The CO2 sonde was shown to be a useful instrument for observing and monitoring the vertical profiles of CO2 concentration in the troposphere.

Because of the increased temporal and spatial resolutions of the sensors onboard recently launched satellites, satellite-based surface aerosol concentration, which is usually estimated from the aerosol optical depth (AOD), is expected to become a strategic tool for air quality studies in the future. By further exploring the relationships of aerosol concentrations and their optical properties using ground observations, the accuracies of these products can be improved. Here, we analyzed collocated observations of surface mass concentrations of fine particulate matter (PM2.5) and black carbon (BC), as well as columnar aerosol optical properties from a sky radiometer and aerosol extinction profiles obtained by multi-axis differential optical absorption spectroscopy (MAX-DOAS), during the 2019–2020 period. We focused the analyses on a daily scale, emphasizing the role of the ultraviolet (UV) spectral region. Generally, the correlation between the AOD of the fine fraction (i.e., fAOD) and the PM2.5 surface concentration was moderately strong, regardless of considerations of boundary layer humidity and altitude. In contrast, the fAOD of the partial column below 1 km, which was obtained by combining sky radiometer and MAX-DOAS retrievals, better reproduced the variability of the PM2.5 and resulted in a linear relationship. In the same manner, we demonstrated that the absorption AOD of the fine fraction (fAAOD) of the partial column was related to the variability of the BC concentration. Analogous analyses based on aerosol products from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) confirmed these findings and highlighted the importance of the shape of the aerosol profile. Overall, our results indicated a remarkable consistency among the retrieved datasets, and between the datasets and MERRA-2 products. These results confirmed the well-known sensitivity to aerosol absorption in the UV spectral region, they also highlighted the efficacy of combined MAX-DOAS and sky radiometer observations.

Two Japanese cultivars of rice (Oryza sativa L.), Hinohikari and Nikomaru, were planted using potting soil on June 13, 2018, and were exposed to elevated CO2 from June 26 to October 9 using open-top chambers. The study was conducted in Nagasaki, in the Kyushu region of Japan, where the air temperature is relatively high. There were two treatments: ambient CO2 treatment with approximately 400 µmol mol–1 (ppm) CO2, and elevated CO2 treatment with approximately 550 ppm CO2. The elevated CO2 treatment significantly increased the net photosynthetic rate and whole-plant dry mass of the two rice cultivars. However, this treatment did not produce significant effects on grain yield and adversely affected grain appearance quality of both cultivars. Among the yield components, spikelet fertility was significantly reduced by exposure to elevated CO2. These adverse effects were typical manifestations of heat stress in rice. Even under ambient CO2 treatment, there was relatively low spikelet fertility and grain appearance quality, because air temperature during the cultivation period was higher than the standard climatological normal of air temperature. Furthermore, under elevated CO2 treatment, significant reductions in transpiration rate of flag leaves were observed during the flowering period. This may cause an increase in temperature of the canopy, including the panicle, and induce heat stress. These results suggest that elevated CO2 could induce heat stress in rice via reduction in transpiration under high air temperature conditions.

By understanding the sources and temporal variations of nitrated mono- and di-aromatic hydrocarbons (nitroaromatic hydrocarbons, NAHCs) in ambient particles, we can evaluate their impact on the climate, environment, and human health. This work quantifies (for the first time) a series of NAHCs (3,5-dinitrosalicylic acid, 2,4-dinitro-1-naphthol, 4-nitrophthalic acid, and 2-hydroxy-5-nitrobenzyl alcohol) in ambient particles collected from an urban site in Nagoya, Japan. The data were collected throughout the day/night cycles during the summer and fall of 2013. To evaluate the possible sources of the NAHCs, the observed NAHC concentrations were compared with organic tracers of anthropogenic secondary organic aerosols (ASOAs) and biomass burning. Nitrocatechols were mainly influenced by emissions from biomass burning during the fall, and by secondary formation from anthropogenic volatile organic compounds (AVOCs) during the summer. In both seasons, AVOC oxidation mainly produced nitrosalicylic acids, 4-nitro-1-naphthol, and 4-nitrophthalic acid, whereas biomass burning in the fall produced a significant amount of 4-nitro-1-naphthol. The concentrations of 3,5-dinitrosalicylic acid and 4-nitrophthalic acid were highly correlated with those of other ASOA tracers, and were strongly related to wind direction, oxidant concentration, and solar radiation. Therefore, these NAHCs are suggested as new tracers of ASOA. Meanwhile, although 2-hydroxy-5-nitrobenzyl alcohol was generated by AVOCs photo-oxidation during the day, its concentration remained high at night, indicating additional nighttime sources such as nitrate radical reactions. Our results suggest that different NAHCs could have different sources, large seasonal and day-to-night variations in their major ones.

Spectroscopic techniques have been widely used for the measurements of aerosol optical properties mainly to examine their impact on radiation balance in the Earth's atmosphere. The ratio of light scattering to extinction, namely single-scattering albedo, is one of the most important parameters to determine whether aerosol particles heat or cool the atmosphere. To measure this ratio, several types of aerosol albedometer based on a combination of two different spectroscopic techniques have been developed recently. This chapter starts by introducing the importance of the radiative impact of aerosol particles and the basic principle of light interaction with particles. The optical parameters of particles and the principle and characteristics of spectroscopic instruments to measure aerosol optical properties are described. Recent progress from the intercomparison of these spectroscopic instruments and applications of spectroscopic techniques to laboratory and observational studies of aerosol optical properties are also introduced.

In this paper, we evaluate the optical properties of low-loss Y-branched multimode polymer optical waveguide couplers with graded-index (GI) cores fabricated by different methods: the Mosquito method and the imprint method in order to apply them to coarse wavelength division multiplexing (CWDM) transmission. We confirm the low insertion loss of those waveguides regardless of fabrication method in a wavelength range from 850 to 1060 nm for CWDM. Furthermore, we succeeded in transmitting a 26 Gbps signal through the GI waveguide at 850-nm wavelength.

The change in the ozone production rate on reducing its precursors, namely, ozone production sensitivity, is important information for developing a strategy to reduce ozone. We expanded a conventional sensitivity analysis theory by including peroxy radical loss by uptake onto particle surfaces in the aim of examining their potential impact. We also propose a new concept of absolute sensitivity that enables us to evaluate the quantitative effectiveness of precursor reduction toward mitigating ozone production over a given period and area. This study applies the theory to observations in Tsukuba, a city in Japan. The relative sensitivity analysis shows that ozone production was more sensitive to volatile organic compounds (VOCs) in the morning and evening, and it became more sensitive to NOx in the afternoon. NO depletion was a main trigger in this sensitivity regime transition. The absolute sensitivity analysis indicates that the VOC-sensitive period in the morning determines the total ozone production sensitivity in a day. While particles did not have significant impact on regime classification in Tsukuba, they have a potential to decrease the mitigating effect of VOC reduction on ozone production and to moderate the enhancement effect of NOx reduction depending upon uptake coefficients. A further study will benefit from a combination with an observation-constrained box model simulation or chemical transport modeling system, which may provide sensitivity analysis over a large spatial and temporal range.

Oxidation of isoprene by hydroxyl radical (OH), ozone (O3), or nitrate radical (NO3) leads to the formation of secondary organic aerosol (SOA) in the atmosphere. This SOA contributes to the radiation balance by scattering and absorbing solar radiation. In this study, the effect of oxidation processes on the wavelength-dependent complex refractive index (RI) of SOA generated from isoprene was examined. Oxidation conditions did not have a large effect on magnitude and wavelength dependence of the real part of the RI. In the case of SOA generated in the presence of sulfur dioxide (SO2), significant light absorption at short visible and ultraviolet wavelengths with the imaginary part of the RI, up to 0.011 at 375 nm, was observed during oxidation with OH. However, smaller and negligible values were observed during oxidation with O3 and NO3, respectively. Moreover, in the absence of SO2, light absorption was not observed regardless of the oxidation process. There was an empirical correlation between the imagin...

A year-long observation of PM2.5 concentrations was conducted in Hanoi from July 2016 to June 2017 using newly developed highly sensitive sensors. The hourly concentration data of PM2.5 agreed well with corresponding data obtained with a beta attenuation monitor located 3 km away, with R2 = 0.73. The monthly variation showed that levels of PM2.5 were high during the dry season, particularly in December (median = 62 µg m–3) and low during the rainy season, particularly in June and July (medians = 19 µg m–3). Haze episodes of PM2.5 with levels higher than 100 µg m–3 were observed 13 times during the dry season (October 2016–March 2017). These episodes may be linked to the East Asian winter monsoon, as the daily levels of PM2.5 and CO increased several days after most of the cold surge events. Two events were investigated further at a higher temporal resolution. For both events, peaks of PM2.5 appeared at midnight for some days after a cold surge, while CO levels often increased during rush hours. For the first event, brief peaks of PM2.5 with a high rate of increase (~5 µg m–3 min–1) were observed, highlighting the importance of a high temporal resolution for PM2.5 sensors in assessing health effects. For the second event, a broad peak of PM2.5 with a gradual increase was observed along with high CO levels. This research reveals the characteristics of PM2.5 haze episodes in Hanoi, which should be studied further to effectively manage air pollution.

Field measurements performed in the Keihin coastal industrial area during summer 2019 were used to characterize the air quality and ozone production potential. The total hydroxyl radical (OH) reactivity was found to be moderate, peaking with a 2-h average of 29.0 s−1, corresponding to an OH lifetime of ∼34 ms. The average hourly total OH reactivity was 11.4 ± 5.2 s−1 (average ± standard deviation), and the measured OH sinks (from over 90 trace species) accounted for 92.3% of the total OH reactivity. Compared with a previous series of campaigns in urban/suburban Japan, this field work investigated an area often overlooked for atmospheric observations and found the smallest missing OH reactivity (on average, 0.88 s−1). The near-zero missing OH reactivity indicated that photochemical procedures were less important to the Yokohama air quality study (AQUAS–Yokohama) than the ubiquitous substantial secondary products in other areas. This study also demonstrated that oceanic air masses may quickly flush coastal industrial areas and that a limited activity of photochemistry due to elevated NOx effectively terminates OH radical recycling. A comparison with other campaigns in Japan exhibited a positive correlation with oxidants (ozone and formaldehyde), indicating secondary products have a critical role in explaining missing OH reactivity. The ozone production potential was corresponding to a volatile organic compound (VOC)-limited regime, while the missing OH reactivity led to an ∼8% increase in ozone formation. Finally, a positive correlation was found between the ozone production rate and the reactivity ratio between VOCs and NOx, in both the current study and various other field campaigns in urban areas.

As a new approach to investigating formation processes of secondary organic aerosol (SOA) in the atmosphere, ozone-induced potential aerosol formation was measured in summer at a suburban forest site surrounded by deciduous trees, near Tokyo, Japan. After passage through a reactor containing high concentrations of ozone, increases in total particle volume (average of 1.4 × 109 nm3/cm3, which corresponds to 17% that of pre-existing particles) were observed, especially during daytime. The observed aerosol formations were compared with the results of box model simulations using simultaneously measured concentrations of gaseous and particulate species. According to the model, the relative contributions of isoprene, monoterpene, and aromatic hydrocarbon oxidation to SOA formation in the reactor were 24, 21, and 55%, respectively. However, the model could explain, on average, only ∼40% of the observed particle formation, and large discrepancies between the observations and model were found, especially around noon and in the afternoon when the concentrations of isoprene and oxygenated volatile organic compounds were high. The results suggest a significant contribution of missing (unaccounted-for) SOA formation processes from identified and/or unidentified volatile organic compounds, especially those emitted during daytime. Further efforts should be made to explore and parameterize this missing SOA formation to assist in the improvement of atmospheric chemistry and climate models.

A new palm-sized optical PM2.5 sensor has been developed and its performance evaluated. The PM2.5 mass concentration was calculated from the distribution of light scattering intensity by considerin...

Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO2 and water vapour were observed. The isotope ratios of both CO2 and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ^13C–CO2 and δ^18O–CO2 increased, while δ2H–H2Ov and δ^18O–H2Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO2 and water vapour and the meteorological phenomena. Therefore, isotopic information of CO2 and H2Ov could be used as a tracer of meteorological information.

Ion-induced nucleation by cosmic rays influenced by solar modulation is of interest, and several studies with radioactive sources or accelerator beams have been performed. We focused on ionization with high-linear energy transfer (LET) particles, such as protons, neutrons, and ions, in secondary cosmic rays and the ion density of the secondary cosmic rays near the ground using the excel-based program for calculating atmospheric cosmic-ray spectrum (EXPACS). According to the calculation, not only muons but also protons and neutrons leave substantial traces of solar modulation at an altitude of 3 km from the ground. To verify the ion-induced nucleation by these secondary high-LET cosmic rays, a chamber experiment was conducted at the accelerator facility HIMAC. Using a chamber with a capacity of 75 L, experiments were conducted by irradiating protons and nitrogen ion beams with a constant energy of 180 MeV/u with varying intensity. The experimental results confirm that the ion density and aerosol density increased as the beam intensity increased. The aerosol density was found to be proportional to the ion density, but irrelevant to the ionization density. It was concluded that the ion-induced nucleation by high-LET secondary cosmic rays, such as protons and neutrons, provides no evidence of enhancement owing to ionization density and cannot account for the claimed variation of cloud formation due to the solar modulation.

In this paper, we represent low-loss Y-branched multimode polymer optical waveguides with graded-index (GI) cores applicable to an optical coupler as a MUX device in coarse wavelength division multiplexing links. We apply the Mosquito method as well as the imprint method to form the Y-branched structures in polymers. We experimentally confirm that the insertion loss (including the coupling, propagation, bending, and multiplexing losses) in the multimode GI-core Y-branched waveguide is approximately 1-dB lower than the same Y-branched waveguide with step-index (SI) core. In addition, we also succeeded in fabricating Y-branched single-mode polymer waveguides applying the Mosquito method. In order to satisfy the single-mode condition, the core diameter needs to decrease to 10 mm and less.

A novel, practical observation system for measuring tropospheric carbon dioxide (CO2) concentrations using a non-dispersive infrared analyzer carried by a small helium-filled balloon (CO2 sonde), has been developed for the first time. Onboard calibrations, using CO2 standard gases, is possible to measure the vertical profiles of atmospheric CO2 accurately with a 240–400 m altitude resolution. The standard deviations (1σ) of the measured mixing ratios in the laboratory experiments using a vacuum chamber at a temperature of 298 K were approximately 0.6 ppm at 1010 hPa and 1.2 ppm at 250 hPa. Compared with in situ aircraft data, although the difference up to the altitude of 7 km was 0.6 ± 1.2 ppm, this bias and difference were within the precision of the CO2 sonde. In field experiments, the CO2 sonde detected an increase in CO2 concentration in an urban area and a decrease in a forested area near the surface. The CO2 sonde was shown to be a useful instrument for observing and monitoring the vertical profiles of CO2 concentration in the troposphere.

In this paper, Y-branched multimode polymer optical waveguides are fabricated using the Mosquito method for applying them to multiplexing (MUX) devices for WDM transmission.

Formation of biogenic secondary organic aerosol (BSOA) and its subsequent evolution can modify the hygroscopicity of the organic aerosol component (OA) in the forest atmosphere, and affect the concentrations of cloud condensation nuclei (CCN) there. In this study, size-resolved aerosol hygroscopic growth at 85 % relative humidity and size-resolved aerosol composition were measured using a hygroscopic tandem differential mobility analyzer and an aerosol mass spectrometer, respectively, at a forest site in Wakayama, Japan, in August and September 2015. The hygroscopicity parameter of OA (κorg) presented daily minima in the afternoon hours, and it also showed increase with the increase of particle dry diameter. The magnitudes of the diurnal variations of κorg for particles with dry diameters of 100 and 300 nm were on average 0.091 and 0.096, respectively, and the difference of κorg between particles with dry diameters of 100 and 300 nm was on average 0.056. The relative contributions of the estimated fresh BSOA and regional OA to total OA could explain 40 % of the observed diurnal variations and size-dependence of κorg. The hygroscopicity parameter of fresh BSOA was estimated to range from 0.089 to 0.12 for particles with dry diameters from 100 to 300 nm. Compared with the use of time- and size-resolved κorg, the use of time- and size-averaged kappa_org leads to under- and over-estimation of the fractional contribution of OA to CCN number concentrations in the range from −4.9 to 26 %. This indicates that the diurnal variations and size-dependence of kappa_org strongly affect the overall contribution of OA to CCN concentrations. The fractional contribution of fresh BSOA to CCN number concentrations could reach 0.28 during the period of intensive BSOA formation. The aging of the fresh BSOA, if it occurs, increases the estimated contribution of BSOA to CCN number concentrations by 50–84 %.