Faculty Profiles - OHATA Sho

Papers - OHATA Sho

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Derivation of the correction factors needed for COSMOS observations at high mass concentrations of black carbon Open Access

Mori, T; Ohata, S; Kondo, Y; Oshima, N; Moteki, N; Hayakawa, Y; Tobo, Y; Sinha, PR; Aggarwal, SG; Malik, A; Koike, M

AEROSOL SCIENCE AND TECHNOLOGY Vol. 59 ( 9 ) page： 1082 - 1094 2025.9

Publisher：Aerosol Science and Technology

COSMOS is a filter-based absorption photometer for long-term observations of black carbon (BC) mass concentrations (M<inf>BC</inf>) in the atmosphere. In environments with very high M<inf>BC</inf>, such as in South Asia, rapid accumulation of BC on the filter tape results in a rapid decrease of filter transmittance (Tr), leading to more frequent filter advances and instrument downtime for changing the filter rolls if the standard threshold setting of Tr (0.7 or 0.8) is applied. Thus, for long-term observations in such environments, correction factors are needed to allow for accurate determination of M<inf>BC</inf> values, even after large decreases of Tr. Here, we compared M<inf>BC</inf> measurements made by two COSMOS instruments with different Tr threshold settings and derived two kinds of correction factors that allow for the derivation of M<inf>BC</inf> at very low Tr while maintaining reasonable accuracy. We found that reliable M<inf>BC</inf> measurements are possible down to Tr ≈ 0.23, depending on the average M<inf>BC</inf> level. The Tr-dependent corrections reflect the effects of two processes: enhancement of absorption of BC by multiple scattering inside the filter, and overlapping of BC accumulated on the filter. The correction factors reported here enable long-term measurements of BC by COSMOS under a wider range of conditions while reducing maintenance costs and the frequency of observation interruptions.

DOI： 10.1080/02786826.2025.2499690

Open Access

Web of Science

Scopus

Evaluation of sample storage methods for single particle analyses of black carbon in snow and ice: Merits and risks of glass and plastic vials for melted sample storage

Ueda, S; Ohata, S; Iizuka, Y; Seki, O; Matoba, S; Matsui, H; Koike, M; Kondo, Y

AEROSOL SCIENCE AND TECHNOLOGY 2025.8

Publisher：Aerosol Science and Technology

Single particle analyses of black carbon (BC) particles in precipitation samples are necessary to elucidate the BC climatic impact attributable to natural and anthropogenic combustion activities. For practical reasons, snow and ice core samples are often melted and stored as liquid in vials before analysis. We evaluated storage methods of samples after melting to assess BC measurement accuracy by transmission electron microscopy (TEM) and a Single Particle Soot Photometer (SP2) combined with a nebulizer. TEM analysis of ultrapure water samples stored in borosilicate glass vials revealed that nebulized particles contained significant amounts of silicate and sodium eluted from glass vials. Because such eluted materials interfere with individual particle observations, plastic vials should be used for TEM analysis. In contrast, mass concentrations and size distributions of BC in snow samples measured by SP2 after 6-week storage as liquid in glass and PET (a plastic) vials were comparable to the initial concentrations and distributions, indicating that interference from glass-eluted materials was negligible for BC measurements by SP2. Repeated measurements of ice core samples revealed that BC mass concentrations and size distributions for both vials remained stable in most of the samples over several months, although significant BC losses occurred in some samples stored in PET vials. The mass concentration vastly decreased (28% on average) after storage for refrozen–thawed snow samples, suggesting it is unsuitable for accurate BC measurement. Our results demonstrate the great importance of vial choice for analyzing nebulized particles, depending on the analytical method and sample storage period. Copyright © 2025 American Association for Aerosol Research.

DOI： 10.1080/02786826.2025.2542900

Web of Science

Scopus

Integrated aircraft and research vessel observational studies of aerosols and clouds in summer over the western North Pacific Open Access

Koike, M; Kawai, Y; Adachi, K; Aiki, H; Kanaya, Y; Kawai, H; Kita, K; Kondo, F; Koshiro, T; Matsui, H; Miyakawa, T; Miyamoto, A; Miyasaka, T; Miyazaki, Y; Mochida, M; Mori, T; Moteki, N; Murayama, T; Nakamura, H; Ohata, S; Oka, E; Okajima, S; Tobo, Y; Sekizawa, S; Yoshida, A

PROGRESS IN EARTH AND PLANETARY SCIENCE Vol. 12 ( 1 ) 2025.7

Publisher：Progress in Earth and Planetary Science

An integrated observational study of aerosols and clouds was carried out in summer 2022 over the western North Pacific (off the eastern coast of Hokkaido, Japan) using both an aircraft and a research vessel for the first time in this area. The aim of this experiment was to characterize the physical and chemical properties of aerosols and to evaluate the contributions of anthropogenic and natural emissions to cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations. The experiment also aims to examine the vertical structure of low-level clouds, which have high radiative effects, over this region. Here, we present an overview of the experiment and some preliminary results. Onboard the research vessel, suspended particulate matter in seawater was sampled, and the size distributions of dominant particle types (e.g., diatom fragments and organic matter) were determined. By analyzing atmospheric aerosols sampled from aircraft, we derived the number size distributions of dust-like particles in the air far from source regions. The aerosol size distributions, as measured from both the vessel and aircraft, suggested that most of the aerosols that could act as CCN were of anthropogenic origin: The upper-bound estimate of the sea spray aerosol (SSA) contribution to the CCN concentration at altitudes below 1200 m was 23%. Numerical model simulations generally reproduced the observed aerosol number concentrations. The simulations supported the inference from the observation that most CCN over the study area were of anthropogenic origin. Using this model, SSA emissions were estimated to account for 9% of the cloud radiative effect. Cloud observations from aircraft revealed that low-level clouds tended to have an adiabatic vertical structure under cold air advection, whereas under warm air advection, they occasionally had a layered structure. Such diverse vertical structures of low-level clouds are not generally seen in the subtropics. The integrated observations carried out in this study provided a basic picture of aerosols and clouds over the study area in summer. Further research is needed to elucidate the roles of aerosols in cloud formation and the radiation budget under various meteorological conditions within the framework of atmosphere–ocean interactions. (Figure presented.)

DOI： 10.1186/s40645-025-00719-1

Open Access

Web of Science

Scopus

Studies of atmospheric climate forcers in the Arctic during the ArCS II project

Koike M., Takigawa M., Morimoto S., Adachi K., Aizawa T., Chandra N., Fujita R., Goto D., Ishidoya S., Ishijima K., Ito A., Kawai K., Kanaya Y., Kim Y., Kinase T., Kondo Y., Machida T., Matsui H., Miyakawa T., Mochida M., Mori T., Moteki N., Murayama S., Ohata S., Oshima N., Patra P.K., Taketani F., Tobo Y., Tohjima Y., Toyoda S., Tsuboi K., Rui O.C., Yahara K., Yamaji K., Yoshida A., Zhu C.

Polar Science 2025.6

Publisher：Polar Science

This paper reviews studies of atmospheric climate forcers, namely, greenhouse gases (GHGs) and aerosols, and their impacts on radiation and clouds in the Arctic during the Arctic Challenge for Sustainability II (ArCS II) project conducted between 2020 and 2024. In GHG research, we measured atmospheric mixing ratios of CO<inf>2</inf>, CH<inf>4</inf>, and N<inf>2</inf>O and their isotope ratios, as well as O<inf>2</inf>/N<inf>2</inf> ratios from the ground, ship (research vessel Mirai), and commercial aircraft over the northern high latitudes. We showed that the rapid increase of CH<inf>4</inf> mixing ratios after ∼2018 could be attributed to elevated microbial CH<inf>4</inf> emissions. The increase of N<inf>2</inf>O after ∼2011 was attributable to an increase of N<inf>2</inf>O emissions from soil treated with chemical fertilizer. In aerosol research, we provided a scientific basis for constructing unified black carbon (BC) datasets in the Arctic and estimated the contributions to Arctic BC from biomass-burning and anthropogenic sources in various regions. We showed the abundance of highly active ice nucleating particles (INPs) increased with rising surface temperatures above 0 °C and evaluated impacts of Arctic dust that serve as INP on clouds. We found that marine biota were likely the sources of cloud condensation nuclei and INPs over the remote Arctic Ocean during periods of high biological activity.

DOI： 10.1016/j.polar.2025.101216

Scopus

Sensitivity of Wintertime Arctic Black Carbon to Removal Processes and Regional Alaskan Sources Open Access

Ioannidis, E; Law, KS; Raut, JC; Marelle, L; Onishi, T; Andrews, E; Ohata, S; Mori, T; Morris, S; Kondo, Y; Sharma, S; Eleftheriadis, K; Klimont, Z; Soulie, A; Granier, C; Quinn, PK; Pratt, KA

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 130 ( 7 ) 2025.4

Publisher：Journal of Geophysical Research Atmospheres

Air pollutants are primarily transported from midlatitude emission regions in winter and early spring, leading to elevated concentrations of aerosols, including black carbon (BC), in the Arctic, a phenomenon known as Arctic haze. The Weather Research and Forecasting model coupled with chemistry is used to investigate potential causes of uncertainties in modeling Arctic BC for winter 2014. The model captures observed variability in BC at surface sites, reproducing BC concentrations at Zeppelin but showing a low bias at Tiksi, Alert, and Utqiaġvik/Barrow. The influence of removal processes on model BC biases is explored by switching off dry or wet deposition. Wet deposition, during transport in the North Atlantic storm track, and locally over Svalbard, dominates BC removal at Zeppelin, while wet removal in the Pacific storm track influences BC at Alert and Utqiaġvik/Barrow. Dry removal over Asian source regions and Alaska affects BC at Utqiaġvik/Barrow, and is larger than wet removal at Tiksi due to the proximity of local/regional anthropogenic sources. Regional runs over northern Alaska in late January show improved simulated BC compared to observations at Utqiaġvik/Barrow, in part, due to better resolution of removal processes, and local/regional emissions. Sensitivity runs also show that regional Alaskan sources, notably from the North Slope of Alaska oil fields, may be contributing 30%–50%, on average, to observed BC at Utqiaġvik/Barrow in January and February 2014, with the remainder from outside the region. These findings highlight the importance of local Arctic emissions, and the need for improved emission inventories in the Arctic.

DOI： 10.1029/2024JD042885

Open Access

Web of Science

Scopus

Aircraft-Based Observation of Mineral Dust Particles Over the Western North Pacific in Summer Using a Complex Amplitude Sensor Reviewed International journal Open Access

Ohata, S; Moteki, N; Adachi, K; Tobo, Y; Matsui, H; Kita, K; Mori, T; Koike, M

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 130 ( 5 ) 2025.3

High-resolution analyses of concentrations and sizes of refractory black carbon particles deposited in northwestern Greenland over the past 350 years – Part 2: Seasonal and temporal trends in refractory black carbon originated from fossil fuel combustion and biomass burning Reviewed International coauthorship International journal Open Access

Kumiko Goto-Azuma, Yoshimi Ogawa-Tsukagawa, Kaori Fukuda, Koji Fujita, Motohiro Hirabayashi, Remi Dallmayr, Jun Ogata, Nobuhiro Moteki, Tatsuhiro Mori, Sho Ohata, Yutaka Kondo, Makoto Koike, Sumito Matoba, Moe Kadota, Akane Tsushima, Naoko Nagatsuka, Teruo Aoki

Atmospheric Chemistry and Physics Vol. 25 ( 1 ) page： 657 - 683 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Copernicus GmbH

Abstract. The roles and impacts of refractory black carbon (rBC), an important aerosol species affecting Earth's radiation budget, are not well understood owing to a lack of accurate long-term observations. To study the temporal changes in rBC since the pre-industrial period, we analyzed rBC in an ice core drilled in northwestern Greenland. Using an improved technique for rBC measurement and a continuous flow analysis (CFA) system, we obtained accurate and high-temporal-resolution records of rBC particle size and mass/number concentrations for the past 350 years. Number and mass concentrations, which both started to increase in the 1870s associated with the inflow of anthropogenically derived rBC, reached their maxima in the 1910s–1920s and then subsequently decreased. Backward-trajectory analyses suggest that North America was likely the dominant source region of the anthropogenic rBC in the ice core. The increase in anthropogenic rBC shifted the annual concentration peaks of rBC from summer to winter–early spring. After rBC concentrations diminished to pre-industrial levels, the annual peak concentration of rBC returned to the summer. We found that anthropogenic rBC particles were larger than biomass burning rBC particles. By separating the rBC in winter and summer, we reconstructed the temporal variations in rBC that originated from biomass burning, including the period with large anthropogenic input. The rBC that originated from biomass burning showed no trend in increase until the early 2000s. Finally, possible albedo reductions due to rBC are discussed. Our new data provide key information for validating aerosol and climate models, thereby supporting improved projections of future climate and environment.

DOI： 10.5194/acp-25-657-2025

On the biases of MERRA-2 reanalysis and ground-based measurements of black carbon aerosols over India Reviewed International coauthorship International journal

Malik, A; Aggarwal, SG; Sinha, PR; Kondo, Y; Ohata, S

ATMOSPHERIC POLLUTION RESEARCH Vol. 16 ( 1 ) 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Atmospheric Pollution Research

The precise measurement of black carbon (BC) and assessment of involved biases are very important considering its serious health and climate effects. MERRA-2 reanalysis data (modern-era retrospective analysis for research and applications, version 2) of surface black carbon (SBC) and ground measurements by optical photometers (mostly Aethalometer) have been used widely to study the temporal and spatial variation of BC aerosol over India. However, a significant bias (more than 70%) between MERRA-2 SBC concentration and ground measurements of BC (by Aethalometer, referred as MBC (AE)) was observed by Malik and Aggarwal (2021). In the current study, the possible reasons for this bias are further evaluated by comparing the MERRA-2 SBC and Aethalometer measurements against a reference photometer, i.e., continuous soot monitoring system (COSMOS). Three-year (2020–2022) SBC concentrations of MERRA-2 reanalysis data are compared against simultaneous measurements of BC by COSMOS (MBC (COSMOS)) at a site in Delhi. Additionally, the biases in ground measurements are further investigated by comparing one-month (March 2023) observations of Aethalometer. These comparison results revealed a 40% underestimation in MERRA-2 reanalysis during 2020–2022. The higher underestimation (50%) of SBC during increased biomass emissions months (October to May), in contrast to the 25% underestimation during conventional emissions months (June to September), emphasizes the underestimation of biomass emissions inputs in MERRA-2 SBC reanalysis. The initial large bias between raw data of Aethalometer (MBC (AE-raw) = 1.92–1.98 times MBC (COSMOS)) get reduced significantly when correction due to multiple scattering factor and mass absorption cross-section (MAC) are incorporated to correct the Aethalometer data (MBC (AE-corr) = 1.15–1.18 times MBC (COSMOS)). The findings of this study underscore the need to harmonize the correction methods for multiple scattering and redefine the MAC values for Aethalometer measurements as well as updating the anthropogenic emission inventories in MERRA-2 SBC reanalysis.

DOI： 10.1016/j.apr.2024.102325

Web of Science

Scopus

Technical note: High-resolution analyses of concentrations and sizes of refractory black carbon particles deposited in northwestern Greenland over the past 350 years – Part 1: Continuous flow analysis of the SIGMA-D ice core using the wide-range Single-Particle Soot Photometer and a high-efficiency nebulizer Reviewed International coauthorship International journal Open Access

Kumiko Goto-Azuma, Remi Dallmayr, Yoshimi Ogawa-Tsukagawa, Nobuhiro Moteki, Tatsuhiro Mori, Sho Ohata, Yutaka Kondo, Makoto Koike, Motohiro Hirabayashi, Jun Ogata, Kyotaro Kitamura, Kenji Kawamura, Koji Fujita, Sumito Matoba, Naoko Nagatsuka, Akane Tsushima, Kaori Fukuda, Teruo Aoki

Atmospheric Chemistry and Physics Vol. 24 ( 22 ) page： 12985 - 13000 2024.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Copernicus GmbH

Abstract. Ice cores can provide long-term records of refractory black carbon (rBC), an important aerosol species closely linked to the climate and environment. However, previous studies of ice cores only analyzed rBC particles with a diameter of < 500 nm, which could have led to an underestimation of rBC mass concentrations. Information on the size distribution of rBC particles is very limited, and there are no Arctic ice core records of the temporal variation in rBC size distribution. In this study, we applied a recently developed improved technique to analyze the rBC concentration in an ice core drilled at the SIGMA-D site in northwestern Greenland. The improved technique, which uses the modified Single-Particle Soot Photometer (SP2) and a high-efficiency nebulizer, widens the measurable range of rBC particle size. For high-resolution continuous analyses of ice cores, we developed a continuous flow analysis (CFA) system. Coupling of the improved rBC measurement technique with the CFA system allows accurate high-resolution measurements of the size distribution and concentration of rBC particles with a diameter between 70 nm and 4 µm, with minimal particle losses. Using this technique, we reconstructed the size distributions and the number and mass concentrations of rBC particles during the past 350 years. On the basis of the size distributions, we assessed the underestimation of rBC mass concentrations measured using the conventional SP2s. For the period 2003–2013, the underestimation of the average mass concentration would have been 12 %–31 % for the SIGMA-D core.

DOI： 10.5194/acp-24-12985-2024

Surface warming in Svalbardmay have led to increases in highly active icenucleating particles Reviewed International coauthorship International journal Open Access

Yutaka Tobo, Kouji Adachi, Kei Kawai, Hitoshi Matsui, Sho Ohata, Naga Oshima, Yutaka Kondo, Ove Hermansen, Masaki Uchida, Jun Inoue, Makoto Koike

Communications Earth & Environment Vol. 5 ( 1 ) page： 516 - 516 2024.9

Controlling factors of spatiotemporal variations in black carbon concentrations over the Arctic region by using a WRF/CMAQ simulation on the Northern Hemisphere scale Reviewed

Yahara K., Yamaji K., Taketani F., Takigawa M., Kanaya Y., Ohata S., Kondo Y., Koike M.

Polar Science 2024.9

Publisher：Polar Science

Black carbon (BC) aerosol, released into the atmosphere from fuel combustion and biomass burning, is known to be an important short-lived climate forcer (SLCF) because it efficiently absorbs solar radiation and directly heats the atmosphere. Because its accumulation on snow and ice promotes their melting, BC is an important driver of warming, particularly in the Arctic region. Observed surface BC concentrations in the Arctic region show typical seasonal variations, increasing during the winter and spring and decreasing during the warmer season with some peak events in few months of summer, along with large interannual variations. The present study investigates the primary factors influencing the differences in the spatiotemporal surface concentrations of BC in the Arctic region by performing a hemispheric-scale air-quality simulation for the years 2015 and 2016. The model reasonably simulates the observed BC concentration levels and their seasonal patterns, as well as their differences between these two years. This study shows that large year-to-year variability in BC-rich air-mass pathways, such as long-range transport from surrounding regions, and besides these air-mass stagnation within the Arctic region, influence the differences in the Arctic BC concentrations between 2015 and 2016. In addition, the Arctic BC concentrations were also controlled by interannual variations in the amount and distribution of emissions due to the size and the location of open fires, including both Asian crop residue burning in spring and boreal forest fires in summer.

DOI： 10.1016/j.polar.2024.101093

Scopus

Source contribution of black carbon aerosol during 2020–2022 at an urban site in Indo-Gangetic Plain Reviewed International coauthorship International journal

Arpit Malik, Shankar G. Aggarwal, Yutaka Kondo, Baban Kumar, Prashant Patel, Puna Ram Sinha, Naga Oshima, Sho Ohata, Tatsuhiro Mori, Makoto Koike, Khem Singh, Daya Soni, Akinori Takami

Science of The Total Environment Vol. 934 page： 173039 - 173039 2024.7

Interference of sea salt in capture vaporizer-ToF-ACSM measurements of biomass burning organic aerosols in coastal locations Reviewed International coauthorship International journal Open Access

Adhitya Sutresna, Melita Keywood, Clare Paton-Walsh, Jack Simmons, Caleb Mynard, Quang Dang, Michihiro Mochida, Sho Ohata, Sonia Afsana, Bhagawati Kunwar, Kimitaka Kawamura, Ruhi Humphries, Erin Dunne, Jason Ward, James Harnwell, Fabienne Reisen, Kathryn Emmerson, Alan Griffiths, Alastair Williams, Robyn Schofield, Peter Rayner

Environmental Science: Atmospheres Vol. 4 ( 6 ) page： 634 - 644 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

Measurements of biomass burning organic aerosols using the capture vaporizer-ACSM are interfered with by sea salt aerosols, as both have m/z 60 as a marker ion and the capture vaporizer is able to detect refractory particles like sea salt.

DOI： 10.1039/d3ea00171g

Mass absorption cross section of black carbon for Aethalometer in the Arctic Reviewed International coauthorship International journal Open Access

Mohit Singh, Yutaka Kondo, Sho Ohata, Tatsuhiro Mori, Naga Oshima, Antti Hyvärinen, John Backman, Eija Asmi, Henri Servomaa, Franz Martin Schnaiter, Elisabeth Andrews, Sangeeta Sharma, Kostas Eleftheriadis, Stergios Vratolis, Yongjing Zhao, Makoto Koike, Nobuhiro Moteki, P. R. Sinha

Aerosol Science and Technology Vol. 58 ( 5 ) page： 536 - 553 2024.5

Composition and mixing state of individual aerosol particles from northeast Greenland and Svalbard in the Arctic during spring 2018 Reviewed International coauthorship International journal Open Access

Kouji Adachi, Yutaka Tobo, Naga Oshima, Atsushi Yoshida, Sho Ohata, Radovan Krejci, Andreas Massling, Henrik Skov, Makoto Koike

Atmospheric Environment Vol. 314 page： 120083 - 120083 2023.12

Evaluation of a method to quantify the number concentrations of submicron water-insoluble aerosol particles based on filter sampling and complex forward-scattering amplitude measurements Reviewed International journal Open Access

Sho Ohata, Nobuhiro Moteki, Hikaru Kawanago, Yutaka Tobo, Kouji Adachi, Michihiro Mochida

Aerosol Science and Technology Vol. 57 ( 10 ) page： 1013 - 1030 2023.10

Physical and chemical properties of PM1 in Delhi: A comparison between clean and polluted days Reviewed International coauthorship International journal

Arpit Malik, Shankar G. Aggarwal, Bhagawati Kunwar, Dhananjay Kumar Deshmukh, Kritika Shukla, Rishu Agarwal, Khem Singh, Daya Soni, Puna Ram Sinha, Sho Ohata, Tatsuhiro Mori, Makoto Koike, Kimitaka Kawamura, Yutaka Kondo

Science of The Total Environment Vol. 892 page： 164266 - 164266 2023.9

A signature of aged biogenic compounds detected from airborne VOC measurements in the high arctic atmosphere in March/April 2018 Reviewed International coauthorship Open Access

Rupert Holzinger, Oliver Eppers, Kouji Adachi, Heiko Bozem, Markus Hartmann, Andreas Herber, Makoto Koike, Dylan B. Millet, Nobuhiro Moteki, Sho Ohata, Frank Stratmann, Atsushi Yoshida

Atmospheric Environment Vol. 309 page： 119919 - 119919 2023.9

Constraining the complex refractive index of black carbon particles using the complex forward-scattering amplitude Reviewed International journal Open Access

Nobuhiro Moteki, Sho Ohata, Atsushi Yoshida, Kouji Adachi

Aerosol Science and Technology Vol. 57 ( 7 ) page： 678 - 699 2023.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Informa UK Limited

Black carbon is the largest contributor to global aerosol's shortwave absorption in the current atmosphere and is an important positive climate forcer. The complex refractive index, m = m(r) + im(i), the primary determinant of the absorbed and scattered energies of incident radiation per unit volume of particulate material, has not been accurately known for atmospheric black carbon material. An accurate value at visible wavelengths has been difficult to obtain due to the black carbon's wavelength-scale irregularity and variability of aggregate shape, distribution in particle size, and mixing with other aerosol compounds. Here, we present a method to constrain a plausible (m(r), m(i)) domain for black carbon from the observed distribution of the complex forward-scattering amplitude S(0 degrees). This approach suppresses the biases due to the above-mentioned complexities. The S(0 degrees) distribution of black carbon is acquired by performing single particle S(0 degrees) measurements in a water medium after collecting atmospheric aerosols into water. We demonstrate the method operating at lambda = 0.633 mu m for constraining the refractive index of black carbon aerosols in the north-western Pacific boundary layer. From the plausible (m(r), m(i)) domain consistent with the observed S(0 degrees) distributions and the reported range of mass absorption cross-section, we conservatively select 1.95 + 0.96i as a recommendable value of the refractive index for uncoated black carbon at visible wavelengths. The recommendable value is 0.17 larger in m(i) than the widely used value 1.95 + 0.79i in current aerosol-climate models, implying a similar to 16% underestimate of shortwave absorption by black carbon aerosols in current climate simulations.

DOI： 10.1080/02786826.2023.2202243

The four-wavelength Photoacoustic Aerosol Absorption Spectrometer (PAAS-4<i>λ</i>) Reviewed International coauthorship International journal Open Access

Franz Martin Schnaiter, Claudia Linke, Eija Asmi, Henri Servomaa, Antti-Pekka Hyvärinen, Sho Ohata, Yutaka Kondo, Emma Järvinen

Atmospheric Measurement Techniques Vol. 16 ( 11 ) page： 2753 - 2769 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Copernicus GmbH

Abstract. In this paper, the Photoacoustic Aerosol Absorption Spectrometer (PAAS-4λ) is introduced. PAAS-4λ was specifically developed for long-term monitoring tasks in (unattended) air quality stations. It uses four wavelengths coupled to a single acoustic resonator in a compact and robust set-up. The instrument has been thoroughly characterized and carefully calibrated in the laboratory using NO2/air mixtures and Nigrosin aerosol. It has an ultimate 1σ detection limit below 0.1 Mm−1, at a measurement precision and accuracy of 3 % and 10 %, respectively. In order to demonstrate the PAAS-4λ suitability for long-term monitoring tasks, the instrument is currently validated at the air quality monitoring station Pallas in Finland, about 140 km north of the Arctic circle. A total of 11 months of PAAS-4λ data from this deployment are presented and discussed in terms of instrument performance. Intercomparisons with the filter-based photometers of a continuous soot monitoring system (COSMOS), the Multi-Angle Absorption Photometer (MAAP), and Aethalometer (AE33) demonstrate the capabilities and value of PAAS-4λ, as well as for the validation of the widely used filter-based instruments.

DOI： 10.5194/amt-16-2753-2023

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Papers - OHATA Sho