Future Vision for
Atmospheric Chemistry 2022-32- Perspectives from Japan -IGAC subcommittee, Science Council of Japan
Japan National Committee of IGAC
Japan Society of Atmospheric Chemistry

Lead Authors

Yugo Kanaya (JAMSTEC)
Hiroshi Tanimoto (NIES)
Nobuyuki Takegawa (Tokyo Metropolitan University)
Michihiro Mochida (Nagoya University)

Contributing authors (from IGAC subcommittee)

Masayuki Takigawa (JAMSTEC)
Mitsuo Uematsu (The University of Tokyo)
Jing Zhang (Toyama University)
Satoshi Inomata (NIES)
Hitoshi Irie (Chiba University)
Nawo Eguchi (Kyushu University)
Yasuko Kasai (Tokyo Institute of Technology)
Jun’ichi Kurokawa (ACAP)
Naoko Saitoh (Chiba University)
Yasuhiro Sadanaga (Osaka Metropolitan University)
Kengo Sudo (Nagoya University)
Tsuyoshi Thomas Sekiyama (Meteorological Research Institute)
Sakae Toyoda (Tokyo Institute of Technology)
Tatsuya Nagashima (NIES)
Tomoki Nakayama (Nagasaki University)
Keiichiro Hara (Fukuoka University)
Jun Hirokawa (Hokkaido University)
Toshinobu Machida (NIES)
Atsuhi Matsuki (Kanazawa University)
Yuzo Miyazaki (Hokkaido University)
Shinji Morimoto (Tohoku University)
Seiichiro Yonemura (Prefectural University of Hiroshima)iAuthors contributing to topical sections

Taku Umezawa (NIES)
Shinichi Enami (Tsukuba University)
Akinori Ito (JAMSTEC)
Hitoshi Matsui (Nagoya University)
Sho Ohata (Nagoya University)
Akira Mizuno (Nagoya University)
Yosuke Niwa (NIES)
Takuya Saito (NIES)
Prabir Patra (JAMSTEC)
Yosuke Sakamoto (Kyoto University/NIES)
Takashi Sekiya (JAMSTEC)
Tamaki Fujinawa (NIES)
Makoto Deushi (Meteorological Research Institute)
Tomohiro O. Sato (NICT)
Shinnosuke Ishizuka (Nagoya University)
Tetsuya Hama (The University of Tokyo)
Akihiko Ito (JAMSTEC)
Kazuhide Matsuda (Tokyo University of Agriculture and Technology)
Akira Tani (University of Shizuoka)
Fumikazu Taketani (JAMSTEC)
Yoko Iwamoto (Hiroshima University)
Jun Nishioka (Hokkaido University)
Yutaka Tobo (NIPR)
Syuichi Itahashi (CRIEPI/Kyushu University)
Naga Oshima (Meteorological Research Institute)Kentaro Suzuki (The University of Tokyo)
Yousuke Sato (Hokkaido University)
Yosuke Yamashita (NIES)
Hideharu Akiyoshi (NIES)
Tomoo Nagahama (Nagoya University)
Tetsu Sakai (Meteorological Research Institute)
Yoshihiro Tomikawa (NIPR)
Hideaki Nakajima (NIES)
Takafumi Sugita (NIES)
Takatoshi Sakazaki (Kyoto University)iiContents
Executive Summary ..................................................................................................................................... 1
1 Ultimate Goals and Past Developments in the Field of Atmospheric Chemistry Research ..................... 3(1) Aims of Atmospheric Chemistry Research.......................................................................................... 3(2) Roots and Historical Development of Atmospheric Chemistry Research .......................................... 5(3) Analysis of Research Trends in the Most Recent 10 Years and Further Challenges......................... 5
2 Issues and Significance of Atmospheric Chemistry Research Today....................................................... 7(1) Efforts to be undertaken in the Next Decade ...................................................................................... 7(2) Social Significance of the Atmospheric Chemistry Research ............................................................. 8(3) Scientific Values of Atmospheric Chemistry Research: Academic Research Direction ................... 10(4) Current Status and Future of Inter-disciplinary Collaboration .......................................................... 12
3 International and domestic collaboration ................................................................................................ 14(1) Collaboration with International Projects .......................................................................................... 14(2) Related Work and Committees of Domestic Ministries and Agencies ............................................. 17
4 Expansion of the platform for atmospheric chemistry research and development and challenges ....... 20(1) Platforms and Resources for Atmospheric Chemistry Research ..................................................... 20(2) Maintenance and Use of Research Data .......................................................................................... 23(3) Human Resource Development ........................................................................................................ 23
Appendix A: Summary from seven topical sections ................................................................................... 26*Full version of "The Future of Atmospheric Chemistry 2022-32," including topical sections (inJapanese), is available at https://jpsac.org/sp1/

iii

Chemistry and Global Pollution (iCACGP) andFuture Earth (FE).

Executive Summary

2 Progress in the past decade, current
challenges, ultimate goals, and identified gaps

1 Background
Global warming, which has been recognized as a
future concern, has now morphed into a "climate
crisis" that threatens our way of life. The root cause
is unquestionably human activities and theincrease in emissions of long-lived greenhousegases (GHGs) such as CO2 and short-lived climate
forcers (SLCFs) including methane (IPCC 6th
Assessment Report, 2021). In addition, healthrisks from atmospheric PM2.5 and ozone are still an
important problem that shortens the life
expectancy of 4 million people per year worldwide(WHO Fact Sheets, 2022), and improvement isstrongly desired. The tasks that the global
atmospheric chemistry research community
undertake have enlarged, from mere scientificclarification of the atmospheric processes of thesetrace constituents, to rationalizing "mitigation
measures" such as emission reductions and theirpathways, assessing uptake and buffering effectsof the natural system, and to bringing about"essential solutions" to both climate and healthproblems, in pursuit of carbon neutral andwellbeing world. In order to fulfill the expectedsocial role with the time-limited goals of carbon
neutrality by 2050 and achievement of the SDGs
by 2030, and to deepen the academic field at thesame time, the basic stance that our research fieldshould have and the research and developmentthat we should promote in the future are clarified inthis "Future Vision of Atmospheric Chemistry 202232" document. This follows up the previous two
publications from the Japan national committee:"Atmospheric Chemistry Research in Japan 19891999: A Review of the Decade and Future
Research
Strategies"
in
2000
and
"Recommendations of the IGAC Subcommittee on
Atmospheric Chemistry Research in Japan" in
2008. This time we choose seven themes anddescribes important R&D directions and issues.
This Future Vision also summarizes the role to beplayed by our field in interdisciplinary, international,
and domestic collaborations, as well as thenecessary facilities, human resource development,
and other issues. In particular, we will discuss how
to best utilize the resources from Japan in theInternational Global Atmospheric Chemistry
Program (IGAC) and its parent organizations, theInternational
Commission
on AtmosphericIn formulating this Future Vision, we first drew up
the "ultimate goal," identified global trends andJapan's strengths toward achieving that goal,
identified important gaps in the current situation,and then proceeded to discuss what initiatives
should be pursued over the next 10 years. As such,the readers can follow the discussion we madeduring its production and enhance his or her
understanding. The review works were conductedin each of the seven sub-themes: "long-lived
gases," "reactive gases," "physical chemistry,""atmosphere-land
integration,""atmosphereocean integration," "aerosols, radiation andclouds," and "stratosphere and mesosphere"(Appendix A). Based on them, the ultimate goals
were summarized into the following three points:
1) Deepening of atmospheric chemistry specificknowledge: For all atmospheric constituents,
including greenhouse gases (GHGs), ozone
depleting substances (ODSs), reactive gases thatcause air pollution, and aerosols, changes in theirconcentrations and properties are to be expressedusing equations and suitable parameters, enabling
explanation of the mechanisms of phenomena andchanges in the real atmosphere and future
prediction. We are to fully understand the roles ofatmospheric chemical processes (emissions,molecular reactions, transport and circulation,
uptake and deposition, etc.) and the mechanismsof functions such as the nature’s oxidizing capacityand purification system.
2) Interdisciplinary exploration of the Earth system:
Interactions of atmospheric chemistry with landand ocean (including biosphere), coupling toclimatesystems(including
cloud/radiationinteractions) and health effects, are systematicallyunderstood.
3) Trans-disciplinary collaboration for solvingsocial issues: Based on a deeper understanding ofthese chemical and the overall Earth systems,
detection of changes in emissions, concentrations,and other key conditions is promptly made, toprovide evidence for mitigation and adaptation
measures for climate change, air pollution, etc.,
and to provide accurate future forecast information1

climate stabilization: Creation of socially relevant
information on emissions and health effects
through introduction of integrated approach on air
pollutants and greenhouse gases and thepromotion of satellite applications.

to society.
In the past decade, "sophistication and integrationof observations and numerical models" and"synthesis of methods for emissions estimation"
have progressed worldwide, and new subjects(from mixing state/size-resolving modeling ofaerosol particles to carbon neutrality) haveemerged. Japanese research has been at theforefront of these new studies, best used its
regional advantages to elucidate the Asian
regional air pollution mechanisms, and has
achieved unique research regarding theatmospheric chemistry theorem (such as OH
radical reactivity evaluations). In addition, ourstrength has been demonstrated in elucidating
sources/sinks of new important substances, suchas iron oxide. At the same time, research structure
has internationalized at IGAC and FE/WCRP(World Climate Research Program) and Japanese
researchers have become more involved.
Meanwhile,
important
substances(polyoxygenated organic compounds HOMs, bioparticles, ice nucleating particles etc.) haveemerged whose cycles and functions need to beelucidated. In addition, the application andadvancement of new methods (satellite
observation, data assimilation, mass spectrometry,
spectroscopic measurement, isotope analysis,etc.) have paved the ways to acquire key scientificknowledge and mechanism understanding in
relationtoclimate/environmental
issues.
Furthermore, there is a need for strengthened
collaboration that transcends the conventional
units of academic research fields, in terms of the
improvement of understanding and modeling of the
Earth system, including the oceans and land, anddialogue with socioeconomic fields. In the future, in
addition to continuing fundamental scientificexploration, we should pursue fundamental
solutions to environmental problems and respondproactively to the demands of society.

B) Explore key processes and systematize
knowledge to solve remaining mysteries inatmospheric chemistry: Discover unknown
processes, resolve inconsistencies between
theory and reality, elucidate nonlinearity andmultiphase chemistry, and gain comprehensive
understanding from molecules to the entire Earth.
C) Interdisciplinary collaboration to improveunderstanding of the Earth system: Elucidationand integrated assessment of interactions(including health effects) and feedbacks among
Earth's subsystems (ecosystems, atmosphericcomposition, climate and weather, humanactivities)D) Enhancement of change detection capability bystrengthening
research
infrastructureandimproving long-term observation systems,
promotion of human resource development,
development of data science and distinctive
international contributions
To accomplish these tasks, we will promote theadvancement of understanding of atmosphericchemical processes within the field, we will actively
strengthen collaboration with neighboring fields(meteorology and climate science, oceanography,
cryosphere research, etc.) and the international
research community to contribute to better
understanding of the Earth system, and to solve
social issues. We will also promote dialogues withevery stakeholder relevant to carbon neutral
society development, including those fromacademy, education, and private sectors as well as
policy makers and citizens, based on state-of-thescience knowledge and data. Such new visions areto be integrated during 2022-2032.

3 Research Targets and Visions in the Next 10
Years
Based on this situation, the "tasks to be
implemented in the next 10 years" were organizedin the seven sub-groups and compiled in a crosssectional manner, which were summarized into thefollowing four points:
A) Gathering of atmospheric chemistry knowledge
that contributes to solving social issues such as2

We are to fully understand the roles of atmosphericchemical processes (emissions, molecular reactions,transport and circulation, uptake and deposition, etc.)
and the mechanisms of functions such as the nature’s
oxidizing capacity and purification system.

1 Ultimate Goals and Past
Developments in the Field of
Atmospheric Chemistry Research

2) Interdisciplinary exploration of the Earth system:
Interactions of atmospheric chemistry with land andocean (including biosphere), coupling to climate
systems (including cloud/radiation interactions) andhealth effects, are systematically understood.

(1) Aims of Atmospheric Chemistry Research
Atmospheric chemistry is a discipline that deals with
the quantity and properties of substances (tracegases and particles) contained in the Earth's
atmosphere, systematically understands the naturaland anthropogenic processes involved in theirchanges, and leads to solutions to problems in the
global atmospheric environment such as global
warming and air pollution. The "ultimate goals" of thisresearch field were reorganized through thediscussion on the formulation of the "Future Vision of
Atmospheric Chemistry 2022-32" as follows.

3) Trans-disciplinary collaboration for solving social
issues: Based on a deeper understanding of thesechemical and the overall Earth systems, detection ofchanges in emissions, concentrations, and other key
conditions is promptly made, to provide evidence for
mitigation and adaptation measures for climatechange, air pollution, etc., and to provide accurate
future forecast information to society.
(*Please refer to Appendix A for the ultimate goals for eachof the seven themes on which the basic work was
conducted: "long-lived gases," "reactive gases," "physicalchemistry," "atmosphere-land integration," "atmosphereocean integration," "aerosols, radiation and clouds," and"stratosphere and mesosphere". The above three goals areaggregate from these sections.)

1) Deepening of atmospheric chemistry specificknowledge: For all atmospheric constituents,
including greenhouse gases (GHGs), ozone
depleting substances (ODSs), reactive gases thatcause air pollution, and aerosols, changes in theirconcentrations and properties are to be expressedusing equations and suitable parameters, enabling
explanation of the mechanisms of phenomena andchanges in the real atmosphere and future prediction.

Figure 1. Conceptual diagram of the future atmospheric chemistry studies during 2022-32. (CC-BY4.0,
https://jpsac.org/sp1/).

3

Table 1. Historical development of Atmospheric Chemistry in Japan.

1960-1979
1980-1989
1990-1999

Research/Societal
topicsPhotochemical smog,
Acid rain
Stratospheric ozone
destruction
Global warming
Global atmosphericchemistry

Approach

Progress, Society and Meetings

Field observations,
Chamber experiments

CACGP (1971)
Aeronomy, Meteorology,
Photochemistry, Chemical kinetics
IGAC (1988)

Aircraft, Research Vessel,
Stratospheric satellite
observations,Campaign/long-term
observations

Dawn of Atmospheric Chemistry
Atmospheric Chemistry Symposium(1991)
IGAC Fuji-Yoshida Conference (1994)
Nobel Prize (S. Rowland, M. Molina,
P. Crutzen, 1995)
Atmospheric Chemistry Discussion
meetings (1995-)
Japan Expert Group of Atmospheric
Chemistry (1999-2013)Nobel Prize (IPCC AR4, 2007)

2000-2009

Megacity, Multiphasechemistry, Climate
model science

2010-2019

Transboundary air
Observation-model
pollution(PM2.5),integration,
radioactive species、Air Systematization
quality

2020-2050

COVID19, SDGs,
carbon neutral, climatechange, adaptation,
disaster prevention

Numerical model,
Tropospheric satellite
observations

Areal continuous /highresolution satellite
observations, Dataassimilation

A conceptual diagram representing the current
activities to goals in the field of atmospheric chemistryresearch is shown in Fig. 1.
The spatial range is from "local" near our living
space and emission sources, to "regional" areas such
as Asia including Japan, or "global" including thepolar regions, and the altitude range is from"troposphere" including "near the surface" to"stratosphere" and "upper layers". As shown in theuppermost part of the figure, the project will treat theentire process from deepening our understanding of"atmospheric chemical processes" and "Earth's
integrated system" to "solving social issues" as one
link in the chain. The chemical substances derived
from both human activities and nature arecomprehensively
treatedas"atmosphericcomposition" to elucidate elementary processes suchas biogeochemical cycles of greenhouse gases,
chemical reactions of reactive gases including
secondary formation of pollutants, and changes in
microphysics and properties of aerosol particles.
These atmospheric constituents are considered as
an important "subsystem" of the global environmental
system, in parallel to human activities, climate andweather, and ocean, land, and ecosystems; thebehavior of the entire Earth system is to be clarified,including interactions and feedbacks among thesefour subsystems. In order to solve social issues, theMatured Atmospheric Chemistry
Japan Society of Atmospheric
Chemistry (2014-)
iCACGP-IGAC Takamatsu
Conference (2018)
Nobel Prize (S. Manabe, 2021)

Publications"Atmospheric
Chemistry
Research in Japan
1989-1999: A
Review of theDecade and Future
Research
Strategies"(2000)"Recommendationsof the IGAC
Subcommittee on
Atmospheric
Chemistry
Research in Japan"(2008)

This work (2023)

results of the natural-science-based analysis of the"current state", such as estimation of "emissions" as
the driving force of modulation of the system, areutilized to make "future projections" based on
simulations, and integrated knowledge such as"causal relationships" based on these results areprovided to policymakers and administrative
agencies to meet "social demands" (right part of Fig.
1). To promote such R&D and solutions to social
issues, strengthening research infrastructure, humanresource development, and deployment of data
science are fundamental elements (lower part of Fig.
1). These fundamentals are common to thedevelopment of Earth and planetary science andenvironmental studies, and we aim to take a leadingrole in these areas in collaboration with many otherfields.
In formulating the "Future Vision for Atmospheric
Chemistry 2022-32," while being conscious of thelong-term achievement of the aforementioned"ultimate goal,", we analyzed the "global trends" ofthe most recent decade and the "strengths of Japan's
R&D efforts" evident during that period and in thehistorical context. Based on this analysis, the current"critical gaps" and further challenges were identified,
and the discussion proceeded to what efforts should
be promoted in the next 10 years. As in the case of4the aforementioned ultimate goal, this work was also
carried out for each of the seven themes (Appendix
A), and then summarized here. Since the text fromthe seven themes exceeded 200 pages, it was
published in separate volumes (Vol. 47 and 48 (linked
from https://jpsac.org/sp1/) of the Archives ofAtmospheric Chemistry Research (AACR), a journalof the Japan Society of Atmospheric Chemistry
publishes). It should be noted that there we aimed tofocus on "edgy" research topics and therefore some
general topics, even if important, might have been left
unmentioned.

well as in the synthesis of multiple approaches inemissions estimations. In the former case, forexample, an atmospheric chemistry transport modelthat expresses the emission distribution of eachchemical species, meteorological fields, andchemical processes was used to interpret theprocesses of observed phenomena, and a newnumerical model that resolves aerosol mixing states
was constructed and verified through observations.
The proportion of papers consisting only ofobservations or numerical models is decreasing. As
for the latter, the "bottom-up method" which estimatesemissions as the product of statistics of activity bysocioeconomic sector (energy conversion, industry,transportation, residential, etc.) and emission factors,
and the "top-down method" which estimatesemissions inversely from observed atmosphericconcentrations, have become more accurate
individually and then synthesized. For example, the
GCP (Global Carbon Project) evaluates bothmethods in an integrated manner, and high-level
reports are published regularly. Furthermore, the last
decade has been characterized by the emergence of
new subjects (from social subjects such as climate
crisis and carbon neutrality to the level of individual
research subjects such as molecular-scale phaseinterfaces, aerosol state/size-specific modeling, etc.).

(2) Roots and Historical Development ofAtmospheric Chemistry Research
Table 1 summarizes the chronology and temporal
evolution of atmospheric chemistry research. Since
the 1990s, research topics have changed along with
global-scale social issues such as stratosphericozone depletion, transboundary air pollution, andglobal warming. In terms of research approaches,
observations that were previously small-scale, havebecome more organized and integrated to larger
scales with the development of satellite observations,etc., and are further being combined with numericalmodel simulations. Atmospheric chemistry, which has
its origins in the fields of upper atmosphere,
meteorology, photochemistry, and reaction kinetics, isnow being studied by an international organization,
the International Global Atmospheric Chemistry
Program (IGAC, hereafter "IGAC"), as well as by theCommission on Atmospheric Chemistry and Global
Pollution, CACGP (now iCACGP). Nobel prize
winners have promoted the research field. In Japan,
the "Japan Society of Atmospheric Chemistry(JpSAC)" and the "IGAC Japan National Committee",serving as a small subcommittee of the Joint
FE/WCRP Subcommittee of the Committee on
Environmental Studies and the Committee on Earthand Planetary Sciences of the Science Council ofJapan" (hereinafter referred to as the "IGAC
Subcommittee") have provided the pivotal initiatives,to organize IGAC international conferences in Japan,
and twice-a-year conferences/symposiums, to foster
discussion forum and develop the researchcommunity.

During the latest decade, "Strengths of Japanese
research" include: new evaluation of iron oxide ofindustrial origin, which has attracted attention as a
new substance affecting climate and ecosystems, byintegrating observations and numerical models toclarify its contribution in reference to theconventionally known naturally occurring mineraldust-derived iron; evaluation of atmosphericoxidation theory through the quantification of the OH
radical reactivity that governs the natural cleansing
process; and the evaluation of source/sink fluxchanges through long-term, high-precision GHGs
observations. Taking advantage of regional
characteristics, we have also progressed withprocess studies and mechanism elucidation of PM2.5transboundary air pollution and have provided
information on the origin contribution to thepolicymakers and stakeholders. Furthermore, during
this period, the organization of research has also
progressed at IGAC and FE/WCRP (World Climate
Research Program), and Japanese researchers havebecome more involved.

(3) Analysis of Research Trends in the Most
Recent 10 Years and Further Challenges

On the other hand, as domestic and international
research progresses, additional new important
substances (e.g., highly oxygenated organic
compounds known as HOMs, bio-particles, ice
nucleating substances, etc.) have been discovered in order to achieve the ultimate goal mentioned earlier,clarification of the circulation and functions of theseIn the course of these developments, during theanalysis of "global trends" with particular attention to
the most recent 10 years, we found that significant
progress has been made in the sophistication andintegration of observations and numerical models, as

5substances is now required in addition to theconventional components. Besides, the application of
new methods (satellite observation, data assimilation,
mass spectrometry, spectroscopic measurement,
isotope analysis, etc.) and the advancement ofexisting technologies have opened the way to obtainkey scientific findings for elucidating natural scientificmechanisms and acquiring important information forsolving social issues, as to be described in the next
two sections. Furthermore, the need for improved
understanding and modeling of the Earth system,
including the oceans and land, the understanding of
impacts from extraterrestrial space, and dialogue withsocioeconomic sectors have emerged, requiring
collaboration beyond the traditional units of individual
disciplines.

62 Issues and Significance ofAtmospheric Chemistry Research
TodayHere, A), B), and C) correspond to 3), 1), and 2) in
Chapter 1, respectively, described as the ultimate
goals, and D) is positioned as the strengthening of
their common foundation.
In A), knowledge will be mobilized to solve social
issues, with a focus on climate stabilization as apressing issue. Sufficient scientific knowledge has tobe obtained by the target year (e.g., carbon neutrality
by 2050, SDGs by 2030, etc.) to disseminate theknowledge to society and promote change. Mitigation
action cycles, evaluating changes of the state of theatmosphere and executing optimized actions have tobe accelerated to satisfy the targets by their specificyears. We have experienced scientific evaluation ofsocietal actions such as reductions of ozonedepleting CFCs under the Montreal Protocol andsulfur limits from marine fuel oil (2020) tightened by
IMO (International Maritime Organization). To
respond to the societal needs of greenhouse gases
evaluation, development of an advanced system toconvert professional observations from "atmosphericenvironment observation satellites," into informationthat can be utilized by society without delay. In
addition, it would be effective to conduct an integrated
analysis of changes in GHGs and air pollutants,
which have been addressed independently. The
advantages of this approach include improving
efficiency of evaluating energy combustion-related
sources and emissions, which are common to both,and the fact that tropospheric ozone and aerosols,
which are the major targets of air pollution mitigation,
are short-lived climate forcing factors (SLCFs) andneed to be managed in an integrated manner with
GHGs to deter global warming. With not only climate
stabilization but also air quality and healthconservation in mind, we will strengthen our analysis
and disseminate scientific information on "emission
changes" and "climate and health impacts," which areemphasized as indicators of society's measures,along with other variables describing gas
concentrations and aerosol properties.

(1) Efforts to be undertaken in the Next
DecadeLooking ahead several decades to the achievementof the ultimate goal described in Chapter 1, andbased on a consideration of historical developments
and the progress made in the last decade, wesummarized the "tasks to be implemented in the next
decade" into the following four points (see moredetails about the tasks of the seven themes inAppendix A).
A) Gathering of atmospheric chemistry knowledge
that contributes to solving social issues such as
climate stabilization: Creation of socially relevant
information on emissions and health effects throughintroduction of integrated approach on air pollutants
and greenhouse gases and the promotion of satellite
applications. {Chapters 6 on Long-lived gases, 3 on
Reactive gases, 4 on Aerosol radiation clouds, 6 on
Stratosphere and mesosphere} {the curly brackets
refer to the chapter number of each topical sections(separate volume, https://jpsac.org/sp1/}.
B) Explore key processes and systematize
knowledge to solve remaining mysteries inatmospheric chemistry: Discover unknown processes,
resolve inconsistencies between theory and reality,
elucidate nonlinearity and multiphase chemistry, andgain comprehensive understanding from molecules
to the entire Earth. {Chapters 3 and 4 in Physical
Chemistry, Chapter 2 in Reactive Gases}.
C) Interdisciplinary collaboration to improveunderstanding of the Earth system: Elucidation andintegrated assessment of interactions (including
health effects) and feedbacks among Earth's
subsystems (ecosystems, atmospheric composition,
climate and weather, human activities) {Atmosphereland integration, atmosphere-ocean integration,
aerosol radiation clouds Chapter 3, stratosphere andmesosphere Chapter 4}.

B) explores the key processes that solve theremaining mysteries in atmospheric chemistry andestablishes theories of the mechanisms that explain
various phenomena. The discussion in the topicalsection included the importance of nitrous acid andheterogeneous reactions that is far from fullunderstanding in the OH radical reaction system
controlling the oxidative capacity of the atmosphere,
and the formation pathway and yield of secondaryproduced aerosols, and atmospheric chemical
reactions in the polar regions. Studies will deepen theunderstanding of elementary processes, improve theunderstanding of "nonlinearity" such as ozoneproducing chemical processes and "multiphaseD) Enhancement of change detection capability bystrengthening research infrastructure and improving
long-term observation systems, promotion of humanresource development, development of data scienceand distinctive international contributions {Chapter 2
on Aerosol Radiation Clouds, Chapter 3 on
Stratosphere and Mesosphere}.

7chemistry" including interfaces and heterogeneous
reactions, and overcome the traditional barriers inlinking local (micro) to global (macro) behavior in thereal atmosphere. A combined process of physics andchemistry with challenges include quantification of
the stratospheric temperature structure andatmospheric circulation changes at mid- and highlatitudes due to the increase in greenhouse gases
and HFCs.

and long-term observations, strengthen the research
infrastructure necessary to accomplish A) through C),
and to foster the next generation of human resources
while introducing new perspectives such as data
science.
How to address the above four issues is also
expressed in the conceptual diagram already shown(Fig. 1). To achieve these tasks, we will promote theadvancement of understanding of atmosphericchemical processes within the field, we will actively
strengthen collaboration with neighboring fields(meteorology and climate science, oceanography,
cryosphere research, etc.) and the international
research community to contribute to better
understanding of the Earth system, and to solve
social issues. We will also promote dialogues withevery stakeholder relevant to carbon neutral society
development, including those from academy,
education, and private sectors as well as policy
makers and citizens, based on state-of-the scienceknowledge and data. Such new visions are to be
integrated during 2022-2032.

C) is to deepen collaboration between atmosphericchemistry and neighboring fields to enhance anintegrated understanding of the Earth system. As
explained in Fig. 1, atmospheric composition isconsidered as one subsystem of the Earth system,and the mechanisms and feedbacks of the interactionof the four subsystems (ecosystem, weather/climate
system, and human activities, and atmosphericcomposition), for example, changes of atmosphericcomposition caused by human activities affectclimate; biogeochemistry influenced from climatechange induces feedback on the ecosystems, are to
be addressed. More specifically, this applies to thestudies clarifying the effects of bioaerosols andsecondary organic aerosols from terrestrial
vegetation on climate/weather processes; changes inthe supply of aerosols and precursors from the ocean
to the atmosphere caused by global warming, ocean
acidification, and changes in nutrient deposition fromthe atmosphere, affecting climate feedbacks via
clouds; aerosol-cloud interactions diagnosed bysimultaneous satellite observations of clouds,
precipitation, and aerosols; and dynamic changes in
Arctic wetlands, permafrost, forest fires, and ocean
circulation and Earth system changes mediated byatmospheric chemistry.

(2) Social Significance of the Atmospheric
Chemistry Research
In August 2021, the Sixth Assessment Report(WG1) of the Intergovernmental Panel on Climate
Change (IPCC) was released, describing that it isunequivocal that the root cause of global warming ishuman activity, which is the result of increased
emissions of CO2, methane, and short-lived climate
forcers (SLCFs), and their concentrations (including
ozone and aerosols) in the atmosphere, changing the
global radiative budget (Fig. 2). It was also estimatedthat only about 0.4°C of temperature increase is left
to achieve the Paris Agreement target of "1.5°C
above pre-industrial levels," and that the amount ofWith the target D), we aim to detect even smaller
signals of change than before by continuing uniqueFigure 2. Contribution to effective radiative forcing (ERF) (a) and global mean surface air temperature (GSAT) change(b) from component emissions between 1750 to 2019 based on CMIP6 models (Thornhill et al., 2021; IPCC AR6 WG1Chapter 6, Figure 6.12).

8

Table 2. WHO air quality guidelines and Japanese environmental standard values for PM2.5 and surface ozone
concentrations.
Air pollutants
Averaging periods
Air Quality Guidelines*
Japaneseenvironmental
WHO (2021)
WHO (2005)
standards
PM2.5 (µg/m3)
Annual5
1015
24 hours
15
25
35
Ozone (µg/m3)
Peak season
60 [ca. 30 ppb]
N/A
60 ppb, 1 hour
8 hours
100 [ca. 50 ppb]
100 [ca. 50 ppb]
* https://iris.who.int/handle/10665/345329

CO2 emissions that can be allowed in the future(remaining carbon budget) is equivalent to only about
12 years of emissions in recent years. In this way, theissue of global warming, which has been recognized
as a concern for the distant future since the end of
the last century, has now changed into a "climate
crisis" that requires urgent action. In 2020, Japan set
a goal of carbon neutrality by 2050, and emission
reductions are being sought in all socio-economic
sectors. In estimating the remaining carbon budget, itis necessary to evaluate the contribution oftemperature increase due to future changes in
SLCFs. Therefore, in addition to CO2, emissions of
SLCFs, substances closely related to air pollution,
have to be well managed together and their climate
impact must be precisely understood.

societal need to respond to the demand for problem
solving in collaboration with adjacent fields andsociety. Moreover, a new mission has emerged, suchas providing evidence based on expertise.
In order to respond to social demands for problem
solving, it is useful to promote natural science
understanding and provide evidence to social
science and policy makers for action, keeping in mind
the concept of DPSIR, which has originated from
Europe as a causal framework for environmental
problems (Fig. 3). DPSIR stands for Driver (rootcause), Pressure (load), State (condition), Impact(effect), and Response (countermeasure or
response). When applied to air quality issues, P
stands for "emissions", S for "change in air
component concentrations", and I for "impact on
climate and health. Scientific clarification of thecausal relationship between them is essential, as tobe shown in Chapter 2 (3). Then, the acquired
knowledge should be smoothly and without delay
deployedtopolicymakers,internationalorganizations, and domestic ministries in an easy-tounderstand manner to promote transformation of D
(global social economy) through R (domestic andinternational measures and responses). We
disseminate expertise in the field to society, forexample, by pinpointing regions and sectors to target
with emission reduction measures, evaluating thecosts and benefits of measures in collaboration witheconomic and social engineering fields, providing
knowledge on the current state of the atmosphereand emissions, future projections, and global
integrated system change, and supporting decision
making. Creating awareness of social transformation
through dialogue with citizens is also important. The
measurement of atmospheric composition by satellite
is expected to make significant progress in terms ofhorizontal resolution, making it possible to trackchanges in GHG emissions by country, city, and evenby individual plant location, which has been difficult in
the past. The visualization of emission reduction
efforts from time to time will be of great significanceto the private sector, which is promoting information
disclosure on its response to climate change issues,

Changes in atmospheric composition are directly
linked not only to climate risks but also to air quality
and health risks; health risks from PM2.5 and ozone
reduce life expectancy by 4 million per year
worldwide (WHO Fact Sheets, 2022), andimprovements are strongly desired. The recent
relationship between atmospheric concentrations
and ambient air quality standards in Japan shows thatthe attainment rate for PM2.5 (daily average 35 μg m3, annual average 15 μg m-3) is improving, but that forphotochemical oxidants (ozone, 60 ppb at 1-hourvalue) is still almost zero. The World HealthOrganization (WHO) has rather tightened theguideline values for 2021 from the viewpoint of
epidemiology, to 5 μg m-3 for PM2.5 and about 30 ppb
for ozone in the peak season (Table 2); therefore,
significant improvements are needed. Furthermore,
the biogeochemical cycles of reactive nitrogen (e.g.,nitric acid) and phosphorus, which are important formarine and terrestrial ecosystems, are said to havecrossed "planetary boundaries" and need to be better
managed, including the atmosphere as a transport
medium.
Under these circumstances, the research field of
atmospheric chemistry, which deals with the scienceof CO2 and air pollutants such as methane, PM2.5,
ozone, and nitrogen oxides, has an increasing

9

Figure 3. Schematic diagram of the linkage with society from the field of atmospheric chemistry (based on expertise inatmospheric chemistry, the causal relationship between socioeconomics - emission loads - atmospheric constituent
concentration state - climate and health effects will be clarified (blue), so that policies based on scientific evidence(yellow) will appropriately lead to social transformation and mitigation of emission loads. In this way, a problem-solving
cycle will be implemented based on the concept of DPSIR (see text). In order to solve problems in the required
timescale, the assessment of emission and concentration changes will be expedited, and the dialogue with policy
makers, international organizations, and national ministries and agencies will be extended (green) regarding the resultsof current analysis and future forecast information. Demonstrate the success or failure of emission reduction policies
through further observations. To accelerate social transformation, we will provide information for private companies andcitizens to make choices. The gears symbolize cause-and-effect relationships and the reliable transfer of information.

driving social change, and risk management through
ESG (Environmental, Social, and Governance)
activities and TCFD (Task Force on Climate-related
Financial Disclosure) reporting. This dimension ofactivity can also generate new services such as
consulting. In this context, it is also important toincrease the number of human resources who canbridge the gap between expertise in atmosphericchemistry and socioeconomic activities.

(3)

Scientific

Valuesofunderdetermined system to the overdetermined
system"and"establishingahierarchicalunderstanding of the system".
In tackling various problems in atmosphericchemistry, we often face the "underdetermined
problem," in which the number of unknowns exceeds
the number of equations because the amount ofobservation is insufficient compared to the number ofvariables to be accurately determined. For example,
even if the atmospheric concentration of a substancecan be accurately measured at a given geographicallocation, that alone does not quantitatively uniquelydetermine the multiple processes that cause changes
in atmospheric concentrations, such as emissions
and chemical production, loss, and inflow fluxes. In
reality, the atmosphere is an open system in whichboundary conditions such as emissions change withtime, and the concentrations and properties of manydifferent substance groups change over four
dimensions (in space and time). The situation isfurther complicated by the fact that only limited
aspects of the true state can be observed, from which
the key processes (sometimes unknown processes)

Atmospheric

Chemistry Research: Academic Research
Direction
Regarding the scientific value and academic
direction of research to be undertaken over the next
10 years, it is clearly important to pursue andunderstand
individual
atmosphericchemicalprocesses(emissions,molecular
reactions,
atmospheric transport, global circulation, natural
uptake and deposition, etc.) in depth, based on
researchers’ sense of curiosity. This section will focus
on two overarching issues: "transition from the10

must be quantitatively evaluated. It is like an attempt
to infer an underlying mechanism or theory from a
jigsaw puzzle with missing pieces. However,atmospheric chemistry transport models, which
represent meteorological fields, dynamics, andchemical processes, have made it possible to link thelimited information from observations, and thus a joint
analysis based on both observations and models isnow being enabled in smarter ways. In the future, itwill be important to move out from this underdetermined state as aided by the increasing amountof observational information combined with intelligent
methods such as data assimilation techniques.

In addition to the use of such multi-component
measurement information with high spatial andtemporal resolution, advanced use of isotopic
information and simultaneous measurement ofconcentrations and fluxes (reactivity) can also
facilitate the transition to an overdetermined system.
Such efforts should be promoted as well in the future.
Another important goal of our research field is toclarify "properties of substances" and their changes,
such as optical properties of aerosols, properties as
cloud condensation nuclei CCN, etc., and indicatorsof health effects including reactive oxygen species.
Therefore, increasing the amount of information on
the properties is essential. Such an approach will be
important to elucidate the full life cycle of primarilyemitted species, those produced in the atmospheresuch as ozone and PM2.5, and yet unidentified
important substances, being affected by natural andanthropogenic emissions, atmospheric chemical
processes, transport processes, and loss processes.
It will also be a useful approach to solving remaining
central problems in atmospheric chemistry, such as
elucidating the behavior of OH radicals, which
dominate atmospheric oxidative capacity and naturalcleansing processes, but whose global-scalevariations are not yet captured.

In recent years, it has become possible to measure
the geographical distribution of concentrations ofmultiple atmospheric constituents from satellites in a
spatially continuous manner and with high horizontal
resolution {Reactive Gases Chapter 2, see thematicvolume for more details}. Geostationary satellites of
the atmospheric environment have also emerged,
making it possible to track temporal variations during
the day. It is significant to analyze multiple
substances in combination in order to unravelcommon processes, as there may be common
emission sources, common transport, relationships
associated with chemical reactions, represented as"covariancerelationships"
amongmultiple
substances. Thus, one of the keys to convert theunderdetermined problem to an overdetermined
system will be to improve the quality and quantity of
information that can be extracted by using dense
temporal and spatial observations of multiple
components and numerical models that are validated
by such observations.

The
secondpoint,"hierarchicalsystemunderstanding," aims to systematically understandthe climate and related materials science. This begins
with the systematization of the understanding within
the field of atmospheric chemistry, for our case, thenpropagates to the higher levels of understanding of
the natural system aspects of the global surface
material cycle, including land and ocean in contact
with the atmosphere, and adds the human dimension
with bi-directional influences. To establish the theoryof atmospheric chemistry, accumulation ofknowledge of elementary reaction process units andsystematization of atmospheric chemical equations
are important. There are many areas that require
further efforts, such as multiphase chemistry
including liquid and gas phases and their interfaces.
There is also a need to better link the chemicalcomposition/microphysical properties of aerosols
with their radiative properties. Simultaneously, it isimportant to gain a systematic understanding of theocean, atmosphere, and land as Earth subsystems,
and to gain a quantitative and consistentunderstanding of the mass exchange fluxes andinteractions among these subsystems and humanactivities. For example, it is important to fullyreconcile the assessment of CO2 exchange between
the land and the atmosphere from the perspective of
atmospheric processes with that from the perspectiveof terrestrial vegetation in order to reach a common
understanding. Lastly, we promote understanding of
the mechanisms of interactions of atmospheric

For example, the Japanese GOSAT-GW satellitewith TANSO-3 sensor, scheduled for launch in fiscal
year 2024, will simultaneously measure CO2 andmethane, which are important GHGs, as well as NO2,
a marker of energy combustion emission sources athigh temperatures, such as cities and power plants.
On the other hand, some small-scaled events arebeyond the reach of satellite observations; therefore,
it is important to expand the Earth observation
network (ground, aircraft, and satellite) in acomplementary manner. Data assimilation methods
that combine information between components andin time and space, and the basic improvement of
atmospheric chemistry transport models that form thebasis for such methods, will be effective for analyzing
such vast amounts of observational information. This
integrated analysis will also require strategies andideas for accurately quantifying uncertainties inseveral important factors and adequately linking themto the analysis of changes in atmosphericcompositional state.

11

chemistry not only with natural systems but also withhuman activities, including the interaction of climatechange with emissions from socioeconomic activities
and anthropogenic land use change, as well as themechanisms of action of health effects caused bychanges in atmospheric composition. With thisapproach, we will be able to deepen atmosphericchemistry research as a discrete field and thenprogressively contribute to interdisciplinary Earthsystem research and even to transdisciplinary
collaboration to solve societal problems. We should
also strive to link the "knowledge" gained about theatmospheric chemistry system to universal
knowledge that can be applied to other systems as
well.

reduction measures for CO2, SLCFs, and air
pollutants are found as potential solutions on thescientific side, they will not be socially effective unlessthey are accompanied by economic rationality. Thus,
the knowledge about the marginal abatement cost
and the cost-benefit analysis becomes significant. It
is also important to provide and disseminate
consulting services and expertise to support ESG
activities and TCFD reporting from private companies
regarding GHG reduction.
The global socioeconomic changes, brought about
by measures to prevent the spread of newcoronavirus infections, can be clearly seen from ourfield's global satellite observations that measure theamount of NO2 in the atmosphere; the changes were
quantified by regions and time periods. This analysis
has virtually evaluated the effects of future emission
controls on air quality improvement and climate
stabilization. In addition, preparing for and tracking
changes in air quality that occur before and after
unexpected and sudden changes in social systems,
for example, nuclear accidents and volcanic
eruptions, is another important interface between
atmospheric chemistry and socioeconomics. The
longer the basic data is maintained, the morevaluable it will be to the scientific community in thefield. The benefit is also used to evaluate theeffectiveness of the control measures taken.

(4) Current Status and Future of Interdisciplinary Collaboration
In order to achieve the 10-year plan as described, in
addition to deepening research and development
within the field, there is a strong need to strengthenor start collaboration with neighboring fields, as
illustrated below.

Earth System Modeling Science
In the CMIP coupled model intercomparison
experiments directly linked to the IPCC report, many
scenario experiments are conducted that include
changes in atmospheric trace gases and aerosols in
addition to the CO2 changes. Two Japanese models,
MRI-ESM2.0 from Meteorological Research Instituteand MIROC-ES2L mainly from Japan Agency for
Marine-Earth Science and Technology (JAMSTEC)
have participated in the experiments, during CMIP6.
Further participation in these Earth system modelexperiments and comparative evaluation of thesemodels, with process-based atmospheric chemistrymodels and with observations, are desirable in the
future. Among the feedbacks between land andocean including ecosystems and atmosphericcomposition, for example, we promote studies onaerosol and ozone formation from the reactions ofbiogenic volatile organic compounds (BVOCs),
evaluation of the impact on climate caused by ice
nuclei formation from bioaerosol/dust particles, andglobal warming feedbacks of further GHGs emissions
due to increased forest fires and thawing permafrost.

Satellite Earth Observation
Earth observation satellites have been closely linked
to the field of atmospheric chemistry. In the past, theatmospheric chemistry community made only limited
connection, e.g., contributions to the development ofsatellite sensors, but recently this activity has
become even more active owing to the continuous
efforts of those involved. In order to rationalize
national-level investment on meaningful Earthobservation satellite projects, the Task Force on
Future Space Development, and its Remote Sensing
Subcommittee, which is jointly managed by various
academic societies, has begun discussions andcoordination across mission applications. The Japan
Society of Atmospheric Chemistry has joined thisactivity and, as an active party, is enhancing
cooperation and mutual understanding by making
proposals such as atmospheric environment
measurements from geostationary satellites and by
evaluating other missions. The Science Council ofJapan's "Subcommittee on the Future Vision of Earth
Observation Satellites", under the Committee on
Earth and Planetary Sciences, also discusses andpromotes the scientific and social significance ofEarth observation satellites (see Chapters 3 and 4).

Economics and Social Engineering
The creation of anthropogenic emission inventories
of CO2 and SLCFs is a direct interface with theeconomic and civil engineering fields; highly accurate
information is essential as a basis for emission
reduction measures. Even if effective emission

Computational Science12

As represented by the supercomputers "Kcomputer" and "Fugaku", remarkable progress has
been seen in computational science, contributing to abetter understanding of a wide range of phenomena
from the molecular level to the global scale (seeChapter 4). As for atmospheric chemistry, there are
already many studies making use of these facilities,
such as theoretical calculations related to aerosols
and other interfacial reactions, and the refinement ofclimate impact predictions for CO2 and SLCFs.
Furthermore, data analysis is now being conductedusing AI and machine learning, which is expected tolead to the discovery of phenomena from weaksignals, that might otherwise be hidden by internalvariabilities in classical statistical analysis.

the atmospheric chemistry research field will bedemonstrated in promoting such research.

On the other hand, the number of experts
specializing in computational science in atmosphericchemistry is limited. The activity has not yet reachedthe level of developing innovative algorithms that
could lead to significant breakthroughs. As a result,many of the atmospheric chemistry process schemes
used in models are basically derived from knowledge
developed in other countries. In the future, it will benecessary to work closely with researchers in themathematicalsciences
who
specialize
incomputational science to develop originality fromJapan's own algorithms. It is hoped that synergistic
effects with the expansion of observational data will
help bridge the gap between observations andmodels.

Health, medicine, and life sciences
There is a long history of research, mainly
epidemiological studies, on factors that adversely
affect health via the respiratory tract, such as ozone
and PM2.5. In recent years, studies that go further into
physical and chemical processes, such as the
dynamics of multiphase and heterogeneous systems
including mass exchange in alveoli, oxidative stressinduced by organic aerosols and peroxides
generated in the atmosphere, or the transfer ofinsoluble solid particles into the circulatory system,
have become active. This is an importantinterdisciplinary area between atmospheric chemistry
and medical and life sciences. In addition to air-borne
infectious diseases such as influenza andcoronaviruses, it is also important to explore therelationship between atmospheric composition andinfectious diseases such as Kawasaki disease, thecause of which is not yet fully identified. Although
Europe and the United States have taken the lead insuch research, it is important to bring about new
developments in epidemiological research andtoxicity assessment based on the sources ofpollutants and climate unique to Asia and the racialcharacteristics of Asia. It is hoped that the potential of13early period of the Japanese atmospheric chemistrycommunity development. It was an opportunity togain recognition and to dramatically increaseinternational exchange and collaboration. In recent
years, about 40% of the participants in international
conferences have been Early Career Scientists(defined by IGAC as graduate students andresearchers within 3 years of receiving their degrees),
and these international conferences are becoming
increasingly important for the development of thenext generation of atmospheric chemists.

3 International and domestic
collaboration(1) Collaboration with International Projects
In atmospheric chemistry research, it is equallyimportant to share and collaborate with theinternational research community in addition to
improving cutting-edge research results in order toachieve a comprehensive understanding of the global
scale and to solve problems.

As of 2023, IGAC is promoting 11 Activities (Table 3)
and 6 Working Groups, each of which plays aleadership and capacity-building role in international
collaboration. These regular activities also play animportant role as a forum for the continued promotion
and development of international collaboration.

The International Global Atmospheric Chemistry
Project (IGAC) and the International Commission on
Atmospheric Chemistry and Global Pollution(iCACGP) play a major role in this international
collaboration. When IGAC was launched, theexecutive committee, called the Scientific Steering
Committee (SSC), consisted mainly of European and
U.S. researchers, but now researchers from Japan,
China, as well as South and Southeast Asia havejoined the SSC and are active in the organization. It
is important for Japan to continue to contributeinternationally through its involvement in the SSC, aswell as to inform the Japanese research communityof global trends and developments.

The topics covered by these Activities often haveoverlap with the topical theme covered by this Future
Vision from Japan; in this context, in addition to theresearchers currently participating from Japan, awide range of age groups, including young
researchers and students from Japan should be able
to be involved in the IGAC Activities in the future toincrease their direct contributions.
The Working Group, on the other hand, is a category
launched by IGAC in 2010 for regions that areimportant for atmospheric chemistry but have weakinternational representation and recognition becauseof the underdeveloped research community in thoseregions. It aims to strengthen grassroots networks ofresearchers and promote international collaboration
with researchers in other regions; currently suchregions include Africa, North and Latin America,
China, Japan, Monsoon Asia, and the Southern
Hemisphere. The Japan National Committee(http://igacproject.org/JapanNationalCommittee),which covers Japan, simultaneously has a role of the

IGAC and iCACGP hold regular international
conferences (to be held jointly every two years after2022) and play an important role as a place where
the seeds of international collaboration are born at
the grassroots and where future leaders are nurtured.
In Japan, the Fujiyoshida Conference in 1994 (about
170 foreign and 90 Japanese participants from 27
countries), the Nagoya Conference in 1997 (about 90
foreign and 90 Japanese participants), and the
Takamatsu Conference in 2018 (725 participantsfrom 45 countries) were successfully held from theTable 3. IGAC’s Activities.
Acronym
Activity
PACES
Air Pollution in the Arctic: Climate, Environment andSocieties
Allin-Wayra
Small sensors for atmospheric science
AMIGO
Analysis of Emissions using Observations
ACAM
Atmospheric Composition and the Asian Monsoon
BBURNED
Biomass Burning Uncertainty: ReactioNs, Emissions
and Dynamics
CCMI
Chemistry-Climate Model Initiative
GEIA
Global Emissions Initiative
MAP-AQ
Monitoring, Analysis and Prediction of Air Quality
CATCH
The Cryosphere and Atmospheric Chemistry
TOAR-II
Tropospheric Ozone Assessment Report -Phase II
DEBITS
Deposition of Biogeochemically Important Trace
Species

14

Japanese translation
北極の大気汚染と気候・環境・社会
大気科学のための小型センサ
大気観測からの排出量解析
大気組成とアジアモンスーン
バイオマス燃焼の不確実性：反応・排出・ダイナミクス
化学気候モデリングイニシアティブ
地球規模の排出量研究イニシアティブ
大気質のモニタリング・解析・予測
寒冷圏と大気化学
対流圏オゾン評価報告書第 2 期
生物地球化学的に重要な微量成分の沈着Figure 4. IGAC’s vision diagram.

IGAC subcommittee of the Science Council of Japan.
These double roles have resulted in increased
international exposure and recognition, as well as in
the domestic fields. Further mutual developmental
relationships should be maintained in the future.
Japan can also play a significant role in the Monsoon
Asia and Oceania Networking Group (MANGO), a
working group in monsoon Asia where atmosphericchemistry researchers had been tied only loosely andnot well connected to the international community.

Of the 17 Goals of the SDGs, atmospheric chemists
can play a significant role in climate change action,clean energy, etc. However, the perspective of "airquality," which affects health, is not easily seen at that
Goals level, and the atmospheric chemistrycommunity needs to work on this issue in the future.
In Asia, in particular, the health hazards of air
pollution and disasters coupled to climate change
may become more serious, and further contributions
from atmospheric chemistry research are needed.
Furthermore, it is important to deepen collaboration
with SOLAS (Surface Ocean-Lower Atmosphere
Study), iLEAPS (Integrated Land EcosystemAtmosphere Processes Study) and with GCP (Global
Carbon Project), which are adjacent fields under the
Future Earth umbrella, to incorporate newperspectives and human resources into atmosphericchemistry as well. As described above, evolution as
an Earth system science and contribution to asustainable society are two important axes for futureatmospheric chemistry research (Fig. 4).

In addition to preparing for the aforementioned
international conference, iCACGP's activities include
planning an IAMAS session on atmosphericchemistry for the International Union of Geodesy andGeophysics (IUGG) international conference. The
position of atmospheric chemistry in Earth systemscience should be reviewed from time to time, suchthat it can serve as an interface platform for broadcollaboration with neighboring fields, including
terrestrial and oceanic chemistry. On the other hand,
Future Earth, an international research program
launched by the International Geosphere-Biosphere
Programme (IGBP) merged with neighboring
programs, is another parent organization of IGAC (inparallel to iCACGP). Future Earth runs Global
Research Networks (GRN), including IGAC, andthere we can ideally play an important role instrengthening
theatmosphericchemistry
community's contribution to society and collaboration
around sustainability. Future Earth has a Japan Hub
with a Secretary General, and is also supported byinstitutions
includingNational
InstituteforEnvironmental Studies and the University of Tokyo.

In addition to IGAC and iCACGP, there are many
otherinternational
research
committees/organizations/bodies with which key
collaboration should be established. The UN and its
international organizations are the good examples.
The World Meteorological Organization (WMO),
through a mechanism called the Research Board,
has established the Environmental Pollution andAtmospheric
Chemistry
Scientific
Steering
Committee(SSC-EPAC)(https://community.wmo.int/governance/commissionmembership/research-board/ssc-epac), a committee

15

closely related to atmospheric chemistry. In particular,
the GAW (Global Atmosphere Watch) Programme
plays an important role in atmospheric monitoring ofgreenhouse gases and air pollutants. GAW has
seven subcommittees relevant to Ozone, UV
radiation, Greenhouse Gases, Aerosols, Precipitation
Chemistry, Reactive Gases, and GURME (Urban
Weather and Environment). The JMA aims for a wide
range of contributions, from involvement in data
centers and data quality control, such as the World
Data Centre for Greenhouse Gases (WDCGG),
which the JMA is responsible for, to the maintenanceof observing stations (even beyond the GAW
stations) and the provision of observation data. Thereis also an Expert Team that discusses and reports on
the technical aspects of research-oriented
infrastructure, and initiatives that link science toservice to society, such as GAFIS (Global Air Quality
Forecasting and Information System), IG3IS(Integrated Global Greenhouse Gas Information
System), covering air quality and health, and urban
greenhouse gas emissions, respectively. The United
Nations Environment Programme (UNEP) has
launched initiatives such as the Climate and Clean Air
Coalition (CCAC) and the International Methane
Emissions Observatory (IMEO) to promote SLCFsrelated research and development and building
international momentum for SLCFs.

Long-lived greenhouse gases and Reactive gases}.
International collaboration is also important interms of climate change issues. In particular, at COP,
the Conference of the Parties to the United Nations
Framework Convention on Climate Change(UNFCCC), each country set policy targets toward2050 carbon neutrality in order to achieve the2°C/1.5°C target of the Paris Agreement. For this,understanding greenhouse gas emissions and theirtrends together with decarbonization pathways, andintegration of reduction strategies of SLCFs areimportant, where atmospheric chemists can play animportant role. In this context, involvement in the
IPCC is also important. The Japanese atmosphericchemistry research community has produced anumber of Author Team members (Lead Author,
Review Editor, etc.) for the Fifth and Sixth
Assessment Reports of the IPCC. Particularly, aseparate chapter on SLCFs has been established in
the Sixth Assessment Report. In the Seventh
Assessment cycle, "2027 IPCC Methodology Reporton Inventories for Short-lived Climate Forcers" is to
be officially produced and contributions with expertisefrom atmospheric chemistry research community are
anticipated. In addition to IPCC, the Arctic Council
has also been working on SLCFs through the
EGBCM (Expert Group on Black Carbon andMethane) and AMAP (Arctic Monitoring andAssessment Program). In particular, in order toreduce black carbon and methane emissions,observer countries of the Arctic Council (including
Japan, China, South Korea, India) that have reported
their emissions are invited to join the Expert Group on
an equal footing with Arctic countries (Canada,
Denmark, Finland, Iceland, Norway, Russia, Sweden,
and the United States), even if they are non-Arctic
countries. The provision of scientific knowledge is a
key element of the Arctic Council's efforts to promote
the conservation and protection of the Arctic. The
related activities from Japan may enhance thecountry’s international position, and from thisperspective, discussions with international legal
scholars and policy makers are also important.

In East Asia, the East Asian Network for Acid
Deposition Monitoring (EANET) started in 2001 has
been playing a major role, and is expected to play afurther role in addressing not only the acid rain but
also ozone/aerosol pollution, and climate change
issues through SLCFs; the potential anticipated fromJapanese atmospheric chemistry researchers
through the Japan-based Asian Center for Air
Pollution Research (ACAP) is great. With regard to
air pollution issues over a wider region, it is also
important to contribute to the Task Force on
Hemispheric Transport on Air Pollution (TF HTAP)
through MICS-Asia (Model Inter-Comparison Study
for Asia), for which ACAP serves as the secretariat.
The CEOS (Committee on Earth Observation
Satellites) under the GEO (Group on Earth
Observations) has been working with the GEOSS(Global Earth Observation System System) todevelop a satellite-based Earth observation system
and its specific groups include AtmosphericComposition-Virtual Constellation (AC-VC). Japan,
while cooperating with South Korea, which launcheda geostationary satellite for observing atmosphericpollutants in 2020, will deepen international
collaboration in terms of Earth observation fromspace and strengthen its leadership in Asia throughpromotion of GOSAT-GW and newly proposed
missions {see topical theme volumes relevant to

Involvementininternational
observational
campaigns and model intercomparison experiments
is also important. For example, NASA has conductedaircraft observations of atmospheric chemistry,
known as the Global Tropospheric Experiment (GTE),
around the world. In Asia, there were the Japanbased PEM-West A and B (1991 and 1994) and
TRACE-P (2001). In 2016, NASA's KORUS-AQ
aircraft observations in Asia were based in Korea,
focusing on a specific area over Korea to directly
observe emissions and chemical transformation fromemission sources. Also in 2018, a German-led
EMeRGe-Asia aircraft observation was based over16

Taiwan. Going forward, NASA plans ASIA-AQ, thesuccessor to KORUS-AQ, in 2024 to observe
emission sources and chemical transformations overa larger area covering East and Southeast Asia in
conjunction with satellites and numerical models.
Aircraft observation is an indispensable element forverifying satellite observations and understanding
integrated
three-dimensional
atmosphericcomposition changes. As Japan has yet to acquire an
aircraft for research purposes, we will continue topropose and encourage the academic community
and ministries to acquire an aircraft dedicated to earth
observation in collaboration with other academic
societies. For the time being, it is also important forJapan to synchronize its involvement in ground andshipboard observations with such opportunities, andto participate by bringing its own originally developed
observation equipment and building up a track record.

many members of JpSAC hold membership of the
Geochemical Society of Japan, the Japan Society for
Atmospheric Environment, the MeteorologicalSociety of Japan, the Oceanographic Society ofJapan, and others, and on some occasions they cosponsor or support research meetings and sessions,thus promoting cooperation with surrounding fields.
In the future, as a field that constitutes the Earth's
surface system, it will be important to determine how
we can contribute to comprehensive scientificunderstanding and how we can effectively
disseminate scientific knowledge to society in termsof our involvement in global environmental issues. In
this regard, the JpSAC's positioning, strengths, andweaknesses should be periodically analyzed, andfuture collaboration should be undertaken with anawareness of complementarity with neighboring
societies.

In all of the above international collaboration, thechallenge is how to effectively disseminate new
findings and mature results from Japan, given thecurrent situation in which the scientific community
tends to be centered on Europe and the United States,
and China is significantly increasing its presence inthe world. Initiatives such as regional reports thatinternational high-level reports rely on, andleadership in the Asia-Oceania region, such as the
Asia Oceania Geosciences Society (AOGS), would
be effective. In addition, Japanese researchers canplay a role in contributing to the creation of
appropriate rules by providing expert perspectives
and fair and neutral evaluations to prevent the spreadof ineffective initiatives and proposals that takeadvantage of carbon neutrality.

We already mentioned that the JpSAC is closely
related to IGAC. But the same also applies to WCRP,
and SOLAS and iLEAPS of Future Earth. The scopeis unique in that it is not limited to the troposphericatmosphere, but also covers the exchange between
the troposphere and stratosphere, the carbon cycle
and reactive materials, and biogeochemistry andinteraction with the terrestrial ecosystem and theocean surface layer. It is resilient to the changing
trends in the discipline and the pressure to restructureorganizations and communities in response tosocietal needs for global environmental issues overthe next 10 to 20 years.

(2)

RelatedWork

andCommittees

Currently, the JpSAC is a cooperative academicorganization of the Science Council of Japan, and it
is important to be involved in diverse activities. The
IGAC subcommittee links Japanese atmosphericchemistry research to the IGAC international
collaboration. It should play the key role in addressing
further issues proposed in the Master Plan for Large
Research Programs and the Future Science
Promotion Initiative, such as how to reconcile
improvements in climate change mitigation with othervalues such as health, energy, and food. Also, ourinvolvement in the Science Council of Japan's"Cross-cutting meetings on Carbon Neutral (Net
Zero)" and the dissemination of the latest findings on
the atmospheric composition changes related toclimate change, not only to Division III (Science andEngineering) of the Science Council of Japan, butalso to Division I (Humanities and Social Sciences)and Division II (Life Sciences) will enhance ourrecognition. The latest trends and issues in this field
are reflected in the "Biennial Report on Research andDevelopment in the Field of Environment andEnergy" published by the Center for Research andDevelopment Strategy, Japan Science andTechnology Agency (JST), and should be used as aofDomestic Ministries and Agencies
The Japan Society of Atmospheric Chemistry(JpSAC), which has its origin in the "Atmospheric
Chemistry Discussion Group (Taiki Kagaku
Kenkyukai)" and "Atmospheric Chemistry Discussion
Meetings (Taiki Kagaku Touronkai)" started in 1999
and 1995, has contributed to the development andcollaboration of atmospheric chemistry researchersin Japan. In 2006, we joined the Japan Geoscience
Union (JpGU), and in 2007, the "Symposium on
Atmospheric Chemistry," one of the two researchmeetings we had been holding, was transformed intothe "Atmospheric Chemistry Session" at the JpGU
regular annual (springtime) meetings. Suchinvolvement in JpGU not only promotes atmosphericchemistry to researchers in other fields, but also
serves to strengthen ties with Earth science fields
related to atmospheric chemistry. In addition to JpGU,

17

Table 4. Japanese domestic and governmental committees to which Atmospheric Chemistry research community
contributes.
省庁・委員会等
Discussion contents
Ministry, committee
環境省中央環境審議会・微小粒子状 It discusses measures to reduce domestic concentrations of PM2.5 and物質等専門委員会
photochemical oxidants (ozone) and to achieve standard values from an(MOE, PM2.5 and O3 committee)
expert perspective, taking into account the effects of transboundary air
pollution and decarbonization.
経済産業省 VOC 排出削減効果の定
From the viewpoint of economic and industrial promotion, the committee is
量的評価に向けた検討等業務検討会 considering measures to promote the reduction of VOCs as precursors ofozone, taking into account regional and industry-specific characteristics(MITI, VOC reduction committee)
rather than a uniform domestic approach, and is discussing the scientificbasis for such measures from a professional standpoint.
文部科学省・気象庁・環境省・経済 Organized mainly by the author team members of IPCCAR6, it exchanges
産業省 IPCCAR6WG1 国内幹事
information among chapters and WGs and discusses how to expand
会、IPCCAR6 国内連絡会
Japan's contribution to the IPCC.
(4 ministries, IPCC committee)
国土交通省気象庁品質評価科学活動 Provides expert opinions and scientific and technical advice on the quality
懇談会
improvement of measurements of GHGs, ozone, aerosols, radiation, etc. in(JMA, GAW related observational accordance with the WMO/GAW Global Atmospheric Monitoring Program
quality assurance)
conducted by the Japan Meteorological Agency.
文部科学省地球観測推進部会
Implementation policies and plans are formulated to promote earth(MEXT, GEO related committee)
observation in cooperation with related ministries and agencies.

starting point for future cross-disciplinary efforts.

respond to these developments without delay andwith scientific rationality, it is important for the
research community side to start preparation andexamination requesting smooth administrative
support and also to lead the IPCC's new activity. In
this way, there is much that can be done from theresearch side to strengthen cooperation among
administration, practice, and research.

The followings are the examples of contributions torelevant tasks and committees of domestic ministries
and other organizations that use atmosphericchemistry expertise to translate scientific findings into
solutions to societal problems (Table 4). Though notincluded in the table, other committees that meet on
a permanent or ad hoc basis include the Ministry of
the Environment's Committee on Continuous
Monitoring of Air Pollution and the Japan Aerospace
Exploration Agency's Committee on Satellite
Observation Missions.

Atmospheric chemists can play a significant role not
only at the national level, but also at the local
government level, contributing to environmental
impact assessment committees of prefectures andcities. In doing so, we could contribute more in the
future to "decarbonization," the reduction ofgreenhouse gas emissions resulting from humanactivities. The Japanese government has set a
reduction target of carbon neutrality in 2050 and a
46% reduction in greenhouse gas emissions in 2030
(compared to 2013 levels), which is also a global
commitment. Despite the internationality, specificmeasures and verification are often localized andhandled at the municipal level. Atmosphericchemistry, which deals with not only greenhousegases but also air pollutants emitted into theatmosphere from anthropogenic or natural sources,
covers not only the construction of emission
inventories of these substances but also inverse
analysis estimating emissions from atmosphericconcentration changes. This will lead to improved
emission knowledge on a real-time basis to facilitate
reduction measures and contribute to simultaneous

These activities should be further expanded in the
future in response to the growing social needs toaddress global climate change and air pollution
issues. Another possibility would be to lead policy
contributions and increase flexibility there. For
example, the Ministry of the Environment submits the"Annual National Report on Black Carbon/Methane
Emissions" to the EGBCM of the Arctic Council via
the Ministry of Foreign Affairs, but the process iscomplicated because multiple departments are
involved affected by the jurisdiction of the ministry. It
is difficult to say that the ministry, which is the point ofcontact, is currently well connected to researchers
who have accurate information and cutting-edge
scientific knowledge. The IPCC has officially decided
to develop a methodology report for the SLCF
inventory in the 7th Assessment cycle, and theprocess has started as of 2023. In order for Japan to18

mitigation of climate change and air pollution. Such
research and development are currently being
conducted at the subcontinent and national level, butwith future improvements in observation andmodeling techniques, it will become possible tounderstand the current situation at the city/street
scales, and the time will come when local
governments can make a more direct policy
contribution to decarbonization and air pollution
control measures.
Despite such an important role, there are significant
challenges regarding the long-term maintenance andcoordination of Earth observation related toatmospheric chemistry: since the "Strategy for the
Promotion of Earth Observation" document publishedin 2004, related to the GEO Strategic Plan, and now
based on the "Implementation Policy for Earth
Observation in Japan in the Next Decade" in 2015,
Japanese ministries including MEXT, the Japan
Meteorological Agency, and the Ministry of theEnvironment have established and maintained
coordinated atmospheric observations. In reality,
however, there are many situations in which eachministry/institution under them has been forced toterminate observations due to budget cuts, such asozone sonde observations. It is desirable tostrengthen the system by, for example, enhancing
cooperation between the research community andthe ministries to soften the impact of the terminationof observations. It is hoped to establish the SLCFs
field in the virtual Earth Observation Collaboration
Center, for example, to overcome these difficulties.

19

4 Expansion of the platform foratmospheric chemistry researchand development and challenges(1)

Platforms

andResources

data for Japanese researchers for collaboration. Also,
geostationary satellite observations by the GEMS
mission from Korea, which started recently, will be a
powerful tool for atmospheric chemistry research in
the Asia-Pacific region. It is also important for Japanto promote and strengthen research in collaboration
with these overseas satellite observations. In futuresatellite observation projects, including those we areproposing, it is expected that the dynamics ofatmospheric constituents that have already been
observed by satellite will be better tracked by
improving the temporal and spatial resolution of theobservations, with better characterization of localized
sources such as cities. It is also desirable to expand
the capabilities of detecting and quantifying new trace
constituents such as volatile organic compounds(VOCs). Discussions in the "Earth Observation
Satellite Future Vision Subcommittee" of the "Earthand Planetary Science Committee" of the SCJ, andthose in the "Task Force Meeting and Remote
Sensing Subcommittee," which consists of 25
academic societies, should be continued andproposals for publicly solicited missions should be
pursued for realization. In addition, the Japan Societyof Atmospheric Chemistry should promote industrygovernment-academia collaboration and the use ofdata to solve social issues with CONSEO(Consortium for Satellite Earth Observation), as
being its official member.

for

Atmospheric Chemistry Research
Observations of the dynamics of atmosphericconstituents at various temporal and spatial scales
require multiple platforms for in-situ measurements orremote sensing, depending on the observation target.
Typical platforms that have been used include
satellites for long-term observations over wide areas
and the entire globe, aircraft and ships forunderstanding the spatial distribution of a region, andground stations suitable for long-term monitoring,observations of surface and vertical distribution
conditions, and operation of advanced measurement
equipment.
Satellite observation of trace gases and aerosols is
a powerful method for determining their
spatiotemporal distribution over a wide area, and is
expected to become even more important in
atmosphericchemistry.
Applications
includeevaluation of atmospheric model simulations, source
estimation by inverse calculations, and forecasting by
data assimilation. Japan has successfully conductedsatellite observations of CO2 and methane with the
GOSAT series (GOSAT, GOSAT-2). An observation
mission with a third satellite (GOSAT-GW, to belaunched in FY2024), which will add NO2, is underpreparation. The areal continuum observations withkilometer-class resolution are expected to provide
direct assessment of nonlinear atmospheric chemical
processes and evaluation of individual sources. In
addition, observations of the ozone layer by the
Improved
Layer
Aroundthe
Atmosphere
Spectrometer(ILAS/ILAS-II)
onboardthe
ADEOS/ADEOS-II satellite, and observations of
halogen chemicals involved in ozone depletion by theSuperconductive
Submillimeter-wave
EmissionSounder (JEM/SMILES) onboard the International
Space Station have been made in the past. The
JEM/SMILES is a superconducting submillimeterwave radiation sounder aboard the International
Space Station. Atmospheric observation by satellites
is one of the distinctive efforts of Japanese
atmospheric chemistry research, and it is expected tocontribute to the global academic community bycontinuously maintaining and strengthening its
infrastructure. Satellite observations of reactive
gases and aerosols have been continuously
progressing in the United States and Europe,
providing an extremely important base of observation

Aircrafts are excellent platforms for understanding
the spatial distribution of atmospheric constituents,
including vertical profiles, and have strengths in themeasurement of diverse gaseous constituents thatcannot be captured by current satellites and in theobservation of aerosols that have complex properties
such as composition and particle size. Japan's efforts
in atmospheric chemistry research include A-FORCE
aircraft observations and observational researchusing overseas aircraft platforms such as NASA’s
DC-8 during the mission TRACE-P. However, there isvirtually no support system for aircraft observation
research in the Earth science field in Japan;
researched need to rely on the use of short-term
chartered aircraft funded by external sources. This
makes it difficult for domestic researchers toparticipate in aircraft observations. Also, theinfrastructure for accumulating and developing
observation techniques remains extremely weak.
Therefore, it is necessary to expand the scope of
aerial observation by establishing a support system.
In the "Master Plan for the 24th Scientific Research
Program" (Master Plan 2020) of the Science Councilof Japan, "Promotion of Climate and Earth System
Science Research by Aircraft Observation" wasselected as one of the priority large-scale research
programs that should be promoted promptly among
the large-scale scientific research programs. If the20introduction of an aircraft dedicated to Earthobservation as proposed in this plan is realized, it isexpected to greatly advance the acquisition of dataon the dynamics and sources of atmospheric tracegases and aerosols, their interaction with the land
surface and oceans, and their relationship withclimate and weather, which cannot be obtained fromthe ground or satellite platforms. In this plan, it is
proposed that the Center for Orbital and Sub-orbital
Observations at the Institute of Space and EarthEnvironment, Nagoya University, will be the core of
the joint use and operation of the project. In addition,
related to this plan, the Meteorological Society ofJapan has compiled a report entitled "Research Planfor the Promotion of Climate and Earth System
Science System by Aircraft Observation." It is hopedthat related academic institutions and organizations
collaborate and continue to study the introduction ofEarth observation aircraft.

observations by national research institutes incollaboration with private operators are also a
powerful tool for atmospheric chemistry research. In
addition to the use of aircraft, it is worth considering
the use of private platforms for atmosphericchemistry research, for example, drones and otherrelated platforms. In collaboration with the private
sector, it is necessary to pay attention to theestablishment of a stable and fundamental
observation system, since there is an aspect of
relying on the generosity of the private sector. Recent
examples of aircraft observations in the East Asia
region include the NASA research project KORUSAQ, an aircraft observation study of the area aroundthe southern Korean Peninsula conducted incooperation between U.S. and South Korean
researchers. Japan's commitment to international
aircraft observations in the Asian region should also
be strengthened. In addition, the use of balloons iseffective for the observations to the stratosphere, andthe establishment of a sustainable observation
system is desirable.

In the CONTRAIL (Comprehensive Observation
Network for Trace gases by AIrLiner) project, aircraft

Figure 5. Domestic ground-based observation sites (red: JMA; blue and gray: supersites and stations maintained by
the research community and laboratories; green: remote sensing measurement points. Background fill is troposphericNO2 column concentration from satellite TROPOMI. (emission distribution can be read), contour lines are typical springnear-surface ozone concentration distribution from data assimilation TCR-2)

21

Vessels are an important platform for understanding
spatial distribution over the ocean, which cannot becovered by ground-based observations. Generally,
the degree of freedom of the observation equipmentthat can be installed is much greater than that ofaircraft, which have strict limitations on payload
capacity. Shipboard observations are also important
for research on chemical processes unique to ocean
regions. It is also an important platform forunderstanding the atmospheric environment in thepolar regions. The availability of opportunities formarine atmospheric observations is comparatively
favorable, using the academic research vessels
Hakuho Maru/Shinsei Maru and the oceanographic
research vessels including R/V Mirai. However, thenumber of projects targeting atmospheric chemistryobservation is not necessarily abundant, and there is
still plenty of room for the atmospheric chemistry field
to take the lead in shipboard observation. A new
Arctic research vessel, named Mirai II, which iscurrently under construction for delivery in FY2026,
will be operated by the Japan Agency for MarineEarth Science and Technology (JAMSTEC) and willcontinuously measure the basic components ofatmospheric composition. JAMSTEC should serve asa focal point for national and international
collaborative
observations,accommodating
additional equipment from other institutions toenhance the comprehensiveness of the researchcruise missions. It is also important to continue
discussions on a future successor to the Antarctic
research vessel Shirase.

concentration and particle size is still lacking, andshould be expanded in the future with a view tocontributing to the assessment of the climate impactof aerosols.
The development of research platforms is not only
necessary in atmospheric observations, but also inlaboratory experimental studies to understand theelementary processes of atmospheric chemistry. In
particular, large reaction chambers are powerful tools
in experiments to trace chemical transformations ofgaseous components and aerosols. The smog
chamber at the National Institute for Environmental
Studies (NIES) has been a central platform forchamber experiments in Japan, and has produced
important results. Since the maintenance andmanagement of the chambers and associatedinstrumentation at the individual researcher level isan excessive burden, it is desirable for theatmospheric chemistry community to consider the
maintenance and development of reaction
experiment platforms for the continuation anddevelopment of process research in the future. In
particular, it is desirable to consider linking theplatform of experiments using cloud chambers toatmospheric chemistry research on themes related to
ice crystal nuclei, etc., in addition to the use ofchambers for tracking chemical reactions. The issueof new particle formation in the atmosphere is an
important remaining issue that covers gases andaerosols with trace atmospheric components, but the
CLOUD experiment at the European Organization for
Nuclear Research (CERN) is currently the only facility
enabling such research on the mechanism of newparticle production. It is desirable for Japan to commit
itself to such advanced experimental researchoverseas, and to consider its own experimental
platform for taking the lead in indoor experimental
research.

Ground-based observation networks (Fig. 5) are
important platforms for both long-term monitoring andintensive observations of atmospheric processes
usingadvanced
instrumentation.
Long-termmonitoring platforms include the Cape Hedo
Atmospheric and Aerosol Monitoring Station of the
National Institute for Environmental Studies, theFukue Atmospheric Environment Observatory
maintained by Chiba University as a representative
institution, and the Noto Supersite of Kanazawa
University. The Ministry of the Environment's network(EANET) of long-term monitoring of air pollutants andacid deposition covering the north and south East
Asia is also unique, and it is hoped to continue. In
particular, the community has made significant
achievements in the field of atmospheric chemistry in
the long-term observation of pollutant outflows fromthe Asian continent on islands and coastal areas, andtherefore its maintenance and development arestrongly desired in the future. Domestic facilities are
sometimes inferior to the facilities and equipment at
Korean supersites, for example, and this is even abarrier to inviting Western researchers to conduct
international joint observation and research. The
ground-based observation system for aerosol

Computers are an essential research resource innumerical model simulations widely used in
atmospheric chemistry. Atmospheric chemistry
simulations can be roughly classified into online
models coupled with weather and climate models andoffline models that take the calculation results ofweather and climate models as input data. In theformer case, the number of forecast variables
increases dramatically, resulting in a very large
increase in CPU resources and memory usage. In thelatter case, in addition to these, storage resources
and I/O communication costs will increase markedly.
Because of the burden of transferring data files, onpremise or private cloud servers are often used. Onpremise servers, i.e., servers in the form ofequipment installed and operated in a facility
managed by the user, include RIKEN's Fugaku, theEarth Simulator of the Japan Agency for Marine-Earth22

Science and Technology, and large computers ofvarious organizations. But in the future, options may
expand to the use of public cloud servers and virtual
servers. Currently, we are in a transitional period from
actual equipment to virtual equipment, and ascomputer performance and available resources
develop, it is desirable to actively propose andpromote atmospheric chemistry research that takes
advantage of them. At present, atmosphericsimulation relies heavily on large parallel computers
equipped with vector or scalar conventional CPUs,
while general-purpose computers equipped with
GPUs for machine learning calculations haverecently become available. In the future, it will bedifficult to achieve the remarkable improvement in
CPU performance that has been achieved so far, andit will be necessary to take into account speed-up
through efficient parallel processing by utilizing GPUs.
In addition to porting old physicochemical model
calculations to GPUs, it will also be necessary todevelop a method to utilize machine learning foratmospheric chemical simulations (so-called proxymodeling). It is necessary to sort out what kind ofcomputer resources will be necessary or available in
the future, depending on the objectives andcalculation methods of atmospheric chemistry
simulations.

necessary to consider how to collect and archive
observation data that are not readily amenable tostandardization,
especiallyforadvancedmeasurements.
Meteorological reanalysis data and emission
inventories have long been shared, mainly throughoverseas efforts, and are important resources foratmospheric modeling research and other studies.
The maintenance and development of these researchresources, which link experiments and observations
with modeling research, will continue to be importantin the future. In addition to meteorological data
provided by the Japan Meteorological Agency, theEuropean Center for Medium-term Weather
Forecasting (ECMWF), and the National Centers forEnvironmental Prediction (NCEP) in the UnitedStates, there is MERRA-2 provided by the National
Aeronautics and Space Administration (NASA),
which includes information on trace chemical
constituents. In Japan, there are also efforts foraerosol reanalysis products (JRAero) and thesecond-generation chemical reanalysis data set(TCR-2) including reactive gases as well, and further
expansion of data and information on trace
constituents is desired. Regarding emission
inventories, Japan has experience in developing
emission inventories of air pollution- and climatechange-related substances in the Asian region (e.g.,
REAS), and is strongly expected to continue
contributing to the development of inventories for the
Asian region and to the provision of guidelines foremission reduction measures.

(2) Maintenance and Use of Research Data
In recent years, it has become common forresearchers to be required to disclose the data they
use when publishing papers in academic journals,
and the ground is being prepared to promote the useof data among researchers. As data repositories suchas PANGAEA are being developed overseas, it isnecessary to consider how Japan can contribute todata disclosure and use. In the field of atmosphericchemistry, there are many observational variables
and it is expected that higher resolution data will
become even more common in the future, andtherefore, a large-scale storage under stable
operating conditions
with
DOI assignment
functionality would be desirable. It is also desirable topromote discussions on data collection, storage, anddistribution, including coordination with existing
efforts such as the World Data Center forGreenhouse Gases (WDCGG), one of the World
Data Centers (WDC), and the ADS of the National
Institute of Polar Research (NIPR). It is preferrable toconsider efforts to develop or centralize a portal for
all atmospheric chemistry observation data in Japan,
as well as new initiatives that incorporate the needsof the atmospheric chemistry field. In promoting theuse of these atmospheric observation data, it is also
importanttopromotestandardizationofmeasurement methods. In this context, it is also

Investment from academia in data science is
expected to grow further in the future. Even thoughatmospheric chemistry is one of the disciplines that
deals with large data sets, collaboration with data
science could lead to the development of
atmospheric chemistry from new angles. Althoughatmospheric chemistry research using artificial
intelligence approaches is still in its infancy, it is amethod with great potential for future development.
As an example, an effort to apply deep learning tomodel global OH radical fluctuations and analyze thecauses of fluctuations has been reported overseas.
How to improve the current data archiving systemand to develop the infrastructure related to big data
should be considered when promoting the use of
artificial intelligence methods such as machinelearning.

(3) Human Resource Development
For the continued development of atmosphericchemistry in Japan, it is also important to sort out andimprove issues related to the development of human23resources to support it. While opportunities forlearning about chemistry and physics, which form thebasis of atmospheric chemistry, are available insecondary education, opportunities for learning
geology, including topics on climate change and air
quality, which atmospheric chemistry involves, areconsidered to be much less common than in otherscience subjects, mainly due to the subject selection
for university entrance exams. It is desirable toimprove the connection between high schools anduniversities in Earth science education bystrengthening support from the academic community
for geoscience education in high schools and by
developing undergraduate university courses thattake into account students with limited experience inhigh school geoscience studies. Secondary
education institutions are focusing on developing thenext generation of human resources with the ability tosolve environmental and social problems from a
global perspective, with the SDGs and other goals in
mind, and therefore the atmospheric chemistryresearch field could make a strong positive
contribution. In addition, education of atmosphericchemistry in the universities is mainly conducted in
graduate schools, and there are few opportunities for
it to be covered in undergraduate courses. There isroom to consider ways to attract students' interest in
atmospheric chemistry through support forundergraduate education, such as the expansion ofteaching materials that can be easily handled inundergraduate classes. Atmospheric chemistrylaboratories in the graduate school accept a wide
range of students with backgrounds in chemistry andphysics who are interested in global environmental
issues. The fact that this is a field of study in which awide range of expertise, not limited to geoscience,
can be utilized would be regarded as a strength. In
addition, it is desirable to widely promote thepossibility of creating knowledge that directly leads tofundamental solutions to social issues, such as
handling data on the concentration of substances thatserve as improvement indicators for global warming
and air pollution, and presenting effective reduction
measures. Researchers from national research
institutes provide support for higher education in thecapacity of affiliated faculty members. By effectively
utilizing the abundant research resources of theseresearch institutes, human resource development atuniversities could be greatly enhanced.

obtain a permanent post, and the situation is suchthat researchers continue to work for a fixed-term
post and aim to be selected for a permanent post ora tenure-track post (a post that can be transferred topermanent after examination). At universities, inaddition to post-doctoral researchers employed withexternal funds, there are also tenure-track positions
available for young researchers. But there is
generally fierce competition among related fields foreach a position, and therefore the production of
excellent young researchers in atmosphericchemistry to be able to compete is a major key to thecontinuation and development of atmosphericchemistry education at universities. In addition, there
is a concern that academic research positions are not
an attractive option for young people, not only in thefield of atmospheric chemistry, but also in otheracademic fields in Japan, because there areinsufficient competition opportunities for positions. In
addition, with Japan's nominal wages stagnating, thetreatment of researchers, including post-doctoral
fellows at universities or research institutes, may belosing their international competitiveness andhindering the attraction of talented young people fromoverseas. It is necessary to keep a close eye on
whether the situation surrounding employment in thisfield will improve as a result of government measures
to support young researchers.
Enhancing contacts with manufacturing andindustrial sectors related to atmospheric chemistry
would be worth. Collaboration that could lead to thedevelopment of cutting-edge measurement methods
and consulting services would also be considered. It
is worth considering not only from the perspective ofstrengthening atmospheric chemistry research, butalso from the perspective of creating diverse career
paths and exchanging human resources between
industry and academia. Producing human resources
with expertise in atmospheric chemistry to the private
sector and society can be effective. Expectations arehigh for the use of data science for the global
environment, and the use of satellite observation dataon atmospheric composition on the Google EarthEngine, etc., to disseminate this information toindustry and to exchange experts with adjacent fields
will help to secure human resources in a broader
sense. Promotion of gender equality is one of theimportant issues in employment in the field of
atmospheric chemistry. The Japan Society ofAtmospheric Chemistry (JpSAC) is actively
increasing the ratio of women in leadership positions,and the Gender Equality and Human Resources
Development Committee of JpSAC supports
childcare during research meetings and conducts
exchange programs for female members. In addition,
the Committee actively supports and encourages
young people who will lead the next generation both

As a career path for students who have studied
atmospheric chemistry after obtaining their degrees,
there are open positions for young researchers,
mainly at the National Institute for Environmental
Studies and other national institutions, and theemployment situation surrounding young researchers
who have just obtained their degrees is not very poor.
However, as in other academic fields, it is not easy to24nationally and internationally.

also an important duty of Japan's academic
community in the world to contribute to thedevelopment of young researchers overseas. The
short course initiatives for young researchers at theiCACGP-IGAC 2018 international conference held in
Takamatsu is a good example and such activities
should also be spread to the domestic atmosphericchemistry community. It is also promoted that thedomestic joint-use laboratories will take the initiativein inviting young researchers from overseas, leading
to international exchanges in the future.

Atmospheric chemistry is a field of study that deals
with the atmosphere of the entire Earth and issues
common to all humankind, such as global warming,
making it easy to share research subjects withoverseas researchers and to promote international
exchange. Taking this advantage, there is room topromote international human resource development
based on human resource exchange. Proactive
development of international joint research isdesirable, not only for the promotion of atmosphericchemistry research in Japan, but also as anopportunity to foster young researchers in Japan. It is25

Appendix A: Summary from seven topical sections
Table A-1. Summary table for the topic Greenhouse gases and ozone depleting substances(Authors: Taku Umezawa, Yosuke Niwa, Takuya Saito, Naoko Saitoh, Sakae Toyoda)
1. Ultimate Goals  To quantitatively understand the causes of changes in atmospheric concentrations of GHGs and ODS from theviewpoints of emission sources and sinks, and to enable accurate future predictions based on an understandingof the circulation mechanism.
 To provide the international community with accurate information on the origin and distribution of emissions oftarget gases in order to contribute to the formulation of effective emission reduction measures under the Paris
Agreement and the Montreal Protocol.
2. Progress in the  The continuously developed atmospheric observations, emission inventories, atmospheric chemistry transport
past 10 years:
models, and terrestrial ecosystem models have enabled integrated comparative analysis of top-down and bottomglobal
up methods, and an international project for this purpose has been organized, in which many Japanese researchersdevelopment andhave participated.
Japanese The data processing and utilization of column-averaged concentrations of CO2 and CH4 by the Japanese GHG
uniquenessobservation satellite, GOSAT/TANSO-FTS, has made great progress.
 With the entry into force of the Paris Agreement, observation and modeling studies for understanding
anthropogenic GHG emissions at regional and urban scales have been actively conducted.
 The importance of the Asian region as a source of GHG and ODS emissions is increasing, and Japaneseobservation data, which can detect source variability in the Asian region with high sensitivity, is highly valuable,
and continuous provision of high-quality data is required.
 In Japan, unique observation platforms have been developed and maintained not only on the ground but also inballoons, aircraft, and ships, etc., and the results of observations of related tracers that are useful for GHG
circulation analysis have been reported based on the development of unique technologies.
 Atmospheric chemistry transport models and terrestrial ecosystem models have been independently developed
by several research groups in Japan and are highly recognized worldwide.
3. Current major  Observation data for continental inland and tropical regions are still insufficient at the global scale, and evengaps
higher-density observation data are required at the regional and urban scales, but there are significant technicaland cost challenges in maintaining high-precision observations, developing analysis systems, and deploying new
observations.
 Observation data from diverse platforms are increasing dramatically, but there are challenges to fully utilize
diverse data for surface flux inverse analysis, such as ensuring uniform data quality and upgrading models to
make the best use of the data.
4. Key questions  How to evaluate whether the Paris Agreement and Montreal Protocol are working? What kind of spatio-temporaland hypothesis todensity, measurement accuracy, and observation platform observation data are needed? How should model
drive research andanalysis systems be developed to take advantage of diverse observational data?
development
 How will the sources and sinks of GHGs and ODS in the ocean and terrestrial ecosystems and atmosphericduring 2022-32
chemistry change with climate change, ocean acidification, ozone depletion and recovery, etc.? How will Arctic
wetlands, permafrost, and forest fires be particularly affected by potentially dramatic changes?
5. Collaborations GCP, RECCAP, NOAA, AGAGE, IGAC

26

Figure A-1. Schematic diagram of global circulation of CO2, CH4, N2O, and halocarbons.
Selected References (Greenhouse gases and ozone depleting substances)
Aoki, S., T. Nakazawa, S. Murayama & S. Kawaguchi (1992), Measurements of atmospheric methane at the Japanese Antarctic Station,
Syowa, Tellus, 44B, 273‒281.
Akiyama, H., Yan, X. & Yagi, K. (2006), Estimations of emission factors for fertilizer-induced direct N2O emissions from agriculturalsoils in Japan: Summary of available data, Soil Science and Plant Nutrition, 52, 774‒787, doi: 10.1111/j.1747-0765.2006.00097.x
Belikov, D. A. et al. (2013), Simulations of column-averaged CO2 and CH4 using the NIES TM with a hybrid sigma isentropic (s-θ)
vertical coordinate, Atmos. Chem. Phys., 13, 1713‒1732, doi: 10.5194/acp-13-1713-2013.
Belikov, D. A., N. Saitoh, P. K. Patra, & N. Chandra, (2021), GOSAT CH4 vertical profiles over the Indian Subcontinent: Effect of apriori and averaging kernels for climate applications, Remote Sens., 13, 1677, doi:10.3390/rs1301677.69
Chandra, N., S. Hayashida, T. Saeki & P. K. Patra (2017), What controls the seasonal cycle of columnar methane observed by GOSAT
over different regions in India?, Atmos. Chem. Phys., 17, 12633－12643.
Chandra, N. et al. (2021), Emissions from the oil and gas sectors, coal mining and ruminant farming drive methane growth over the past
three decades, J. Meteor. Soc. Japan, 99, 309‒ 337, doi: 10.2151/jmsj.2021-015.
Frey, M. et al. (2019), Building the COllaborative Carbon Column Observing Network (COCCON): long-term
stability and ensemble performance of the EM27/SUN Fourier transform spectrometer, Atmos. Meas. Tech., 12, 1513－1530, doi:
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Fujita, R. et al. (2018). Temporal variations of the mole fraction, carbon, and hydrogen isotope ratios of atmospheric methane in the
Hudson Bay Lowlands, Canada, J. Geophys. Res. Atmos., 123, 4695‒4711, doi: 10.1002/2017JD027972
Fujita, R. et al. (2020). Global and regional CH4 emissions for 1995‒2013 derived from atmospheric CH4, δ13C‐CH4, and δD‐
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Ghosh, A. et al. (2015), Variations in global methane sources and sinks during 1910‒2010, Atmos. Chem. Phys., 15, 2595‒2612, doi:
10.5194/acp-15-2595-2015.
Goto, D., S. Morimoto, S. Aoki, P. K. Patra & T. Nakazawa (2017a), Terrestrial biospheric and oceanic CO2 uptake estimated from longterm measurements of atmospheric CO2 mole fraction, δ13C and δ(O2/N2) at Ny-Alesund, Svalbard, J. Geophys. Res. Atmos., doi:
10.1002/2017JG003845.
Goto, D. et al. (2017b), Vertical profiles and temporal variations of greenhouse gases in the stratosphere over Syowa Station, Antarctica,
SOLA, 13, 224‒229, doi: 10.2151/sola.2017- 041.
Hayashida, S., A. Ono, S. Yoshizaki, C. Frankenberg, W. Takeuchi & X. Yan (2013), Methane concentrations over Monsoon Asia as
observed by SCIAMACHY: Signals of methane emission from rice cultivation, Remote Sens. Env., 139, 246－256.
Hirota, M., K. Nemoto, A. Murata & K. Fushimi (1991), Observation of Carbon Dioxide Concentrations in Air and Surface Sea Waterin the Western North Pacific Ocean, Oceanogr. Mag., 41, 19-28.

27

Iida, Y. et al. (2015), Trends in p CO2 and sea‒air CO2 flux over the global open oceans for the last two decades. J Oceanogr, 71, 637‒
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the NIES-TM‒FLEXPART coupled transport model and its adjoint, Atmos. Chem. Phys., 21, 1245‒1266, doi: 10.5194/acp-21-12452021.
Matsueda, H., H. Y. Inoue (1996), Measurements of atmospheric CO2 and CH4 using a commercial airliner from 1993 to 1994, Atmos.
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Nara, H. et al. (2012), Effect of air composition (N2, O2, Ar, and H2O) on CO2 and CH4 measurement by wavelength scanned cavity
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Nara, H. et al. (2014), Emissions of methane from offshore oil and gas platforms in Southeast Asia, Sci. Rep., 4:6503, doi:
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Nara, H. et al. (2017), Emission factors of CO2, CO and CH4 from Sumatran peatland fires in 2013 based on shipboard measurements,
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Nishihashi, M. et al. (2019), Greenhouse gases and air pollutants monitoring project around Jakarta megacity, IOP Conf. Ser.: EarthEnviron. Sci., 303, 012038, doi: 10.1088/ 1755-1315/303/1/012038.
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Niwa Y. et al. (2014), Seasonal Variations of CO2, CH4, N2O and CO in the Mid-Troposphere over the Western North Pacific Observed
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Niwa, Y. et al. (2017), A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) ‒ Part 2:
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Niwa, Y. et al. (2021), Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and shipobservations, Atmos. Chem. Phys., 21, 9455‒9473, doi: 10.5194/acp-21-9455-2021.
Nomura, S., H. Mukai, Y. Terao, T. Machida & Y. Nojiri (2017), Six years of atmospheric CO2 observations at Mt. Fuji recorded with abattery-powered measurement system, Atmos. Meas. Tech., 10, 667‒680, doi: 10.5194/amt-10- 667-2017.
Nomura, S. et al. (2021), Measurement report: Regional characteristics of seasonal and long-term variations ingreenhouse gases at Nainital, India and Comilla, Bangladesh, Atmos. Chem. Phys., 21, 16427‒16452, doi: acp-21-16427-2021.
Oda, T. & S. Maksyutov (2011), A very high-resolution (1 km×1 km) global fossil fuel CO2 emission inventory derived using a point
source database and satellite observations of nighttime lights, Atmos. Chem. Phys., 11, 543‒556, doi: 10.5194/acp-11-543-2011.

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Patra, P. K. et al. (2016), Regional Methane Emission Estimation Based on Observed Atmospheric Concentrations (2002‒ 2012), J.
Meteorol. Soc. Japan, 94(1), 91‒113, doi: 10.2151/jmsj.2016-006.
Patra, P. K., et al. (2018), Improved Chemical Tracer Simulation by MIROC4.0-based Atmospheric Chemistry- Transport Model(MIROC4-ACTM), SOLA, 14, 91‒96, doi: 10.2151/sola.2018-016.
Patra, P. K. et al. (2021), Methyl chloroform continues to constrain the hydroxyl (OH) variability in the troposphere. J. Geophys. Res..
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Saeki, T. & P.K. Patra (2017), Implications of overestimated anthropogenic CO2 emissions on East Asian and global land CO2 flux
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Sasakawa, M. et al. (2013), Aircraft and tower measurements of CO2 concentration in the planetary boundary layer and the lower freetroposphere over southern taiga in West Siberia: Long-term records from 2002 to 2011, J. Geophys. Res. Atmos., 118, 9489‒ 9498,
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Watanabe, F. et al. (2000), Interannual variation of growth rate of atmospheric carbon dioxide concentration observed at the JMAʼs threemonitoring stations: Large increase in concentration of atmospheric carbon dioxide in 1998, J. Meteorol. Soc. Japan, 78, 673-682.
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Table A-2. Summary table for the topic Reactive gases(Authors: Yugo Kanaya, Kengo Sudo, Prabir K. Patra, Yosuke Sakamoto, Takashi Sekiya, Tamaki Fujinawa,
Hiroshi Tanimoto, Nawo Eguchi, Naoko Saitoh, Yasuko Kasai, Makoto Deushi, Tomohiro O. Sato)
1. Ultimate Goals  Be able to express various processes such as photochemical reactions, atmospheric transport, deposition, etc. inequations and, given emissions and boundary conditions, be able to predict future concentration-time evolution
and budget of a group of atmospheric trace gas constituents. To be able to quantitatively understand the role ofeach process.
 The ability to link the causes of concentration changes to changes in emissions, quantify the contribution of eachcomponent to climate change as short-lived climate forcing factors (SLCFs), including feedbacks, and healtheffects, and to propose mitigation measures.
 The ability to provide accurate chemical weather forecasts to society based on the laws of physics and chemistry.
2. Progress in the  The worldwide progress of satellite observations, high-precision in-situ observations, and standardization has
past 10 years:
greatly improved the spatio-temporal coverage of information on atmospheric constituent concentrations, andglobalhas facilitated the integration of observations and numerical models.
development and  Japan's strengths include: understanding the causes of regional ozone and PM2.5 pollution in East Asia, evaluation
Japaneseof OH radical reactivity and heterogeneous uptake coefficients of radicals, process knowledge from isotopes,
uniquenessdevelopment of multiple Earth system models, progress in atmospheric chemistry transport modeling and data
assimilation, and satellite observation analysis technology developed with GOSAT and others, emission
inventories.
3. Current major  Lack of understanding of the OH radical reaction system, which is at the heart of atmospheric chemistrygaps Lack of understanding of the nonlinearity of ozone chemistry and the spatial distribution of production rate andlimiting factors
 Insufficient quantification of causal relationships between changes in atmospheric composition and emissions,and rapid assessment of emission inventories to optimize reduction measures Lack of information on vertical distribution (including stratospheric) and daily variations even with improved
satellite observations
 Lack of early detection observation information for prediction of sudden events
4. Key questions  Can the gap between methods in global OH estimation (hemispheric gradient, trend) be filled?
and hypothesis to  Will satellite observation systems with kilometer-level horizontal resolution and continuous areal distribution
drive research andand integrated greenhouse gas (GHG)-air quality (AQ) analysis significantly advance our understanding ofdevelopment
nonlinearities and limiting factors in ozone chemistry and our assessment of important emission sources?
during 2022-32
 Can AQ analysis also provide scientific evidence for decision making on climate stabilization?
 If ammonia, VOCs, etc. are integrated into numerical models in addition to NOx, etc., will the prediction ofozone, PM2.5, etc. be improved (will this provide knowledge on food issues in addition to climate change andhealth issues)?
 Can we improve not only chemical weather forecasting and future prediction of the Earth system, but also thecurrent numerical forecast model of meteorology by improving our understanding of the interaction between
atmospheric chemistry, meteorology, and the Earth system, and by incorporating key observation information,
thereby providing useful information to society?
5. Collaborations  IGAC, iCACGP, COSPAR, CEOS, SPARC

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Figure A-2. Estimated NOx emissions from data assimilation system with two different horizontal resolutions
based on OMI satellite observations of tropospheric NO2. (modified from Sekiya et al. (2021))
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over the northwestern Pacific Asian Rim region, Atmos. Chem. Phys., 20, 15003–15014.
Fujinawa, T. et al. (2021). First concurrent observations of NO2 and CO2 from power plant plumes by airborne remote sensing,Geophysical Research Letters, 48, e2021GL092685, doi:10.1029/2021GL092685.
Ha, P. T. M., R. Matsuda, Y. Kanaya, F. Taketani & K. Sudo (2021), Effects of heterogeneous reactions on tropospheric chemistry: aglobal simulation with the chemistry–climate model CHASER V4.0, Geosci. Model Dev., 14, 3813–3841.
Hattori, S. et al. (2021), Isotopic evidence for acidity-driven enhancement of sulfate formation after SO2 emission control, Sci. Adv.,
7(19), eabd4610.
Hayashida, S., M. Kajino, M. Deushi, T. T. Sekiyama & X. Liu (2018), Seasonality of the lower tropospheric ozone over China observedby the Ozone Monitoring Instrument, Atmos. Environ., 184, 244-253.
Inoue, K., K. Tonokura, K. & H. Yamada (2019), Modeling study on the spatial variation of the sensitivity of photochemical ozone
concentrations and population exposure to VOC emission reductions in Japan, Air Qual. Atmos. Health, 12, 1035-1047.
Irie, H. et al. (2021), Continuous multi-component MAX-DOAS observations for the planetary boundary layer ozone variation analysis
at Chiba and Tsukuba, Japan, from 2013 to 2019, Progress in Earth and Planetary Science, 8, 31.
Ishino, S. et al. (2017), Seasonal variations of triple oxygen isotopic compositions of atmospheric sulfate, nitrate, and ozone at Dumontd'Urville, coastal Antarctica. Atmos. Chem. Phys., 17(5), 3713– 3727.
Ishino, S. et al. (2021), Regional Characteristics of Atmospheric Sulfate Formation in East Antarctica Imprinted on 17O Excess Signature,
J. Geophys. Res. Atmospheres, 126, e2020JD033583.
Itahashi, S., R. Mathur, C. Hogrefe, S. L. Napelenok & Y. Zhang (2020), Modeling stratospheric intrusion and trans-Pacific transport on
tropospheric ozone using hemispheric CMAQ during April 2010 – Part 2: Examination of emission impacts based on the higher-orderdecoupled direct method, Atmos. Chem. Phys., 20, 3397–3413.
Kanaya, Y. et al. (2007), Chemistry of OH and HO2 radicals observed at Rishiri Island, Japan, in September 2003: Missing daytime sinkof HO2 and positive nighttime correlations with monoterpenes, J. Geophys. Res., 112, D11308, doi: 10.1029/2006JD007987.
Kanaya, Y. et al. (2012), Comparisons of observed and modeled OH and HO2 concentrations during the ambient measurement period of
the HOxComp field campaign, Atmos. Chem. Phys., 12, 2567–2585.

32

Kanaya, Y. et al. (2019), Ozone and carbon monoxide observations over open oceans on R/V Mirai from 67° S to 75° N during 2012 to
2017: testing global chemical reanalysis in terms of Arctic processes, low ozone levels at low latitudes, and pollution transport, Atmos.
Chem. Phys., 19, 7233–7254
Kanaya, Y. et al. (2020), Rapid reduction in black carbon emissions from China: evidence from 2009–2019 observations on Fukue Island,
Japan, Atmos. Chem. Phys., 20, 6339–6356.
Kohno, N., J. Li, Y. Sakamoto & Kajii, Y. (2020), Rate constants of CH3O2 + NO2 ↔ CH3O2NO2 and C2H5O2 + NO2 ↔ C2H5O2NO2
reactions under atmospheric conditions, Int. J. Chem. Kinet., 53, 571-582.
Kurokawa, T. & T. Ohara (2020), Long-term historical trends in air pollutant emissions in Asia: Regional Emission inventory in ASia
(REAS) version 3, Atmos. Chem. Phys., 20, 12761–12793, doi: 10.5194/acp-20-12761-2020.
Li, J. et al. (2020), Total hydroxyl radical reactivity measurements in a suburban area during AQUAS–Tsukuba campaign in summer
2017. Sci. Total Environ. 740, 139897.
Miyazaki, K. et al. (2017), Decadal changes in global surface NOx emissions from multi-constituent satellite data assimilation, Atmos.
Chem. Phys., 17, 807–837.
Miyazaki, K., et al. (2020a), Evaluation of a multi-model, multiconstituent assimilation framework for tropospheric chemical reanalysis,
Atmos. Chem. Phys., 20, 931–967.
Miyazaki, K. et al. (2020b), Updated tropospheric chemistry reanalysis and emission estimates, TCR-2, for 2005–2018, Earth Syst. Sci.
Data, 12, 2223–2259.
Miyazaki, K. et al. (2021), Global tropospheric ozone responses to reduced NOx emissions linked to the COVID-19 worldwide
lockdowns, Sci. Adv., 7 (24), eabf7460.
Nagashima, T., K. Sudo, H. Akimoto, J. Kurokawa, & T. Ohara (2017), Long-term change in the source contribution to surface ozone
over Japan, Atmos. Chem. Phys., 17, 8231- 8246.
Nakajima, T. et al. (2017), Model depiction of the atmospheric flows of radioactive cesium emitted from the Fukushima Daiichi Nuclear
Power Station accident. Progress in Earth and Planetary Science, 4, 2, doi:10.1186/s40645-017- 0117-x.
Nakashima, Y., N. Kamei, S. Kobayashi & Y. Kajii, (2010), Total OH reactivity and VOC analyses for gasoline vehicular exhaust witha chassis dynamometer. Atmos. Environ. 44, 468-475.
Nakashima, Y. et al. (2014), Total OH reactivity measurements in ambient Air in a southern Rocky Mountain Ponderosa Pine Forest
during BEACHON-SRM08 summer campaign. Atmos. Environ. 85, 1-8.
Oshima, N. et al. (2012), Wet removal of black carbon in Asian outflow: Aerosol Radiative Forcing in East Asia (AFORCE) aircraft
campaign, J. Geophys. Res., 117, D03204, doi:10.1029/2011JD016552, 2012.
Patra, P. et al. (2014), Observational evidence for interhemispheric hydroxyl-radical parity, Nature, 513, 219–223, doi:
10.1038/nature13721.
Patra, P. K. et al. (2017), The Orbiting Carbon Observatory (OCO-2) tracks 2-3 peta-gram increase in carbon release to the atmosphere
during the 2014-2016 El Nino, Sci. Rep., 7, 13567.
Patra, P. K. et al. (2021), Methyl chloroform continues to constrain the hydroxyl (OH) variability in the troposphere. J. Geophys. Res.
Atmospheres, 126, e2020JD033862. doi: 10.1029/2020JD033862.
Sadanaga, Y. A. Yoshino, S. Kato & Y. Kajii (2005), Measurements of OH reactivity and photochemical ozone production in the urban
atmosphere, Environ. Sci. Technol., 39, 8847-8852.
Sakamoto, Y., A. Yabushita, M. Kawasaki & S. Enami, (2009), Direct emission of I2 molecule and IO radical from the heterogeneous
reactions of gaseous ozone with aqueous potassium iodide solution, J. Phys. Chem. A, 113, 7707- 7713, doi: 10.1021/jp903486u.
Sakazaki, T. et al. (2013), Diurnal ozone variations in the stratosphere revealed in observations from the Superconducting SubmillimeterWave Limb-Emission Sounder (SMILES) on board the International Space
Station (ISS), J. Geophys. Res. Atmospheres, 118, 7, 2991—3006, doi: 10.1002/jgrd.50220
Sato, K. et al. (2017), Total OH Reactivity Measurements for the OH-Initiated Oxidation of Aromatic Hydrocarbons in the Presence ofNOx. Atmos. Environ. 171, 272-278.
Sato, T. O., T. Kuroda & Y. Kasai, Novel index to comprehensively evaluate air cleanliness: the Clean aIr Index (CII), Geoscience
Communication, 3, 233-247, doi:10.5194/gc-3-233-2020, 2020.
Sekiya, T. et al. (2020), Global bromine- and iodine-mediated tropospheric ozone loss estimated using the CHASER chemical transportmodel, SOLA, doi: 10.2151/sola.2020-037.
Sekiya, T. et al. (2021), Impacts of horizontal resolution on global data assimilation of satellite measurements for tropospheric chemistry
analysis, J. Adv. Model. Earth Syst., 13, e2020MS002180.
Sekiyama, T. T. & M. Kajino (2020), Reproducibility of surface wind and tracer transport simulations over complex terrain using 5-, 3-,
and 1-km-Grid Models, J. Appl. Meteorol. Climatol., 59, 937-952.
Someya, Y. et al. (2020), Atmospheric ammonia retrieval from the TANSO-FTS/GOSAT thermal infrared sounder, Atmos. Meas. Tech.,13, 309–321.
Sudo, K., M. Takahashi & H. Akimoto (2003), Future changes in stratosphere-troposphere exchange and their impacts on future
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Takashima, H. et al. (2022), Full latitudinal marine atmospheric measurements of iodine monoxide, Atmos. Chem. Phys., 22, 4005–4018,
doi:10.5194/acp-22-4005-2022, 2022.
Takegawa, N. et al. (2004), Removal of NOx and Noy in Asian outflow plume: Aircraft measurements over the western Pacific in January
2002, J. Geophys. Res., 109, doi:10.1029/2004JD004866.
Taketani, F. et al. (2012), Measurement of overall uptake coefficients for HO2 radicals by aerosol particles sampled from ambient air at
Mts. Tai and Mang (China). Atmos. Chem. Phys. 12, 11907-11916.
Taketani, F., Y. Kanaya & H. Akimoto (2013), Kinetic studies of heterogeneous reaction of HO2 radical by dicarboxylic acid particles.

33

International Journal of Chemical Kinetics 45,560-565.
Takigawa, M. et al. (2020), Can Delhi's pollution be affected by crop fires in the Punjab region?, SOLA, 16, 77-80.
Tanimoto, H., K. Ikeda, R. van der A, S. Garivait & K. F. Boersma (2015), Interannual variability of nitrogen oxides emissions fromboreal fires in Siberia and Alaska during 1996–2011 as observed from space, Environ. Res. Lett., 10, 065004.
Toride, K. et al. (2021), Potential of mid-tropospheric water vapor isotopes to improve large-scale circulation and weather predictability,
Geophys. Res. Lett., doi: 10.1029/2020GL091698.
Tsunogai, U. et al. (2010), Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in Eastern Asia using Δ17O, Atmos.
Chem. Phys., 10, 1809–1820, doi: 10.5194/acp-10-1809-2010, 2010.
Ueda, K., H. Nitta & H. Odajima (2010), The effects of weather, air pollutants and Asian dust on hospitalization for asthma in Fukuoka,
Environ. Health Prev. Med., 15, 350-357, doi: 10.1007/s12199-010-0150-5.
Xu, H. et al. (2021), Determination of the triple oxygen isotopic composition of tropospheric ozone in terminal positions using a multistep
nitrite-coated filter-pack system. Rapid Commun. Mass Spectrom. 35, e9124. doi: 10.1002/rcm.9124.
Yamaji, K. et al. (2006), Analysis of the seasonal variation of ozone in the boundary layer in East Asia using the Community Multi-scale
Air Quality model: What controls surface ozone levels over Japan?, Atmos. Environ., 40, 1856-1868.
Yoshino, A. et al. (2012), Air quality diagnosis from comprehensive observations of total OH reactivity andreactive trace species in urban central Tokyo, Atmos. Environ., 49, 51-59.
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34

Table A-3. Summary table for the topic Laboratory experiments and physical chemistry(Authors: Shinichi Enami, Shinnosuke Ishizuka, Tetsuya Hama, Satoshi Inomata)
1. Ultimate Goals Understanding of all physical and chemical processes that occur in the atmosphere.
Derivation of reaction rate constants, uptake coefficients, and photolysis rate constants, taking into accountthe solvent effects of molecular heterogeneity and the peculiarities of interfaces.
Based on the above data, all physico-chemical processes that occur in the atmosphere (chemical composition,
volatility distribution, hygroscopicity, and optical properties for aerosols) can be computationally reproduced
and predicted.

2. Progress in the past 10 years: 
global
development andJapaneseuniqueness

The understanding of gas-phase reactions that lead to the formation of aerosols has been advanced worldwide.
The importance of multiphase reactions involving interfaces has been recognized.
Experimental equipment and theoretical calculations have been developed to elucidate the nature ofinterfaces.
In Japan, original research results based on physical chemistry have been produced.
The rise of emerging Asian countries and Japan's geographical advantages (joint research and personnel
exchange).
3. Current major 
The gap between laboratory experiments (simple systems and high concentrations) and real atmospheres
gaps(complex systems and low concentrations).

The detection of intermediates to determine the formation mechanism of final products.
What fraction of the aerosol components can be analyzed and quantified correctly?
The understanding of the interactions between aerosols and clouds is not sufficient.
The impact of reactions involving oceanic microlayers and ice and snow, where there is mass transfer to andfrom the atmosphere, has not been adequately evaluated.
Interfacial phenomena can only be treated qualitatively and not quantified (e.g., nonlinear increase in reaction
rate constants at the interface).
4. Key questions 
Can we improve the sensitivity of measurement instruments and the accuracy of multi-component
and hypothesis tosimultaneous high time-resolution measurement devices?
drive research and 
Can we correctly understand the formation mechanism of monomers and dimers (especially HOM) in thedevelopment
oxidation process and the chemical reaction process in the particle phase?
during 2022-32
How can we (simply) organize the production yield of secondary aerosols by key factors (oxidants,
temperature, humidity, amount and properties of existing particles)? Are there any other factors that we are
overlooking?
Is it possible to capture the chemical transformation process of aerosols microscopically (e.g., with opticaltweezers)? (Example: Capture aerosols in the air with optical tweezers, keep them for a few days, andmeasure them spectroscopically (Raman, IR). Can we obtain evidence of compositional changes due to OH
oxidation during the day and NO3 oxidation at night?)
Understanding of phenomena peculiar to the interface.
What are the breakthroughs for quantification of heterogeneity (complexity) and interfacial phenomena?
5. Collaborations  IGAC, Molecular Science Society, Synthetic Organic Chemistry

Figure A-3. New particle formation pathways from oxidation of α-pinene (from Inomata (2021)).
Selected References (Laboratory experiments and physical chemistry)
35

Akimoto, H. & J. Hirokawa (2020), Field Observations of Secondary Organic Aerosols, in Atmospheric Multiphase Chemistry, edited,
doi:https://doi.org/10.1002/9781119422419.ch8.
Deng, Y. et al. (2021), Temperature and acidity dependence of secondary organic aerosol formation from α-pinene ozonolysis with acompact chamber system, Atmos. Chem. Phys., 21(8), 5983-6003, doi:10.5194/acp-21-5983-2021.
Enami, S. (2021), Fates of Organic Hydroperoxides in Atmospheric Condensed Phases, J. Phys. Chem. A, 125(21), 4513-4523,
doi:10.1021/acs.jpca.1c01513.
Enami, S., S. Ishizuka & A. J. Colussi (2019), Chemical signatures of surface microheterogeneity on liquid mixtures, J. Chem. Phys.,150(2), 024702.
Enami, S., H. Mishra, M. R. Hoffmann & A. J. Colussi (2012), Protonation and oligomerization of gaseous isoprene on mildly acidic
surfaces: Implications for Atmospheric Chemistry, J. Phys. Chem. A, 116(24), 6027-6032, doi:10.1021/jz100322w.
Enami, S., Y. Sakamoto & A. J. Colussi (2014), Fenton chemistry at aqueous interfaces, Proc. Natl. Acad. Sci. U. S. A., 111(2), 623628, doi:10.1073/pnas.1314885111.
Endo, T. et al. (2018), Spherical Spontaneous Capillary- Wave Resonance on Optically Trapped Aerosol Droplet, J. Phys. Chem. C,
122(36), 20684-20690, doi:10.1021/acs.jpcc.8b03784.
Hatakeyama, S. & H. Akimoto (1994), Reactions of Criegee intermediates in the gas-phase, Res. Chem. Intermed., 20(3-5), 503-524,
doi:10.1163/156856794x00432.
Hiranuma, Y., K. Kaniwa, M. Shoji & F. Mafune (2011), Solvation Structures of Iodide on and below a Surface of Aqueous Solution
Studied by Photodetachment Spectroscopy, J. Phys. Chem. A, 115(30), 8493-8497, doi:10.1021/jp204195t.
Iinuma, Y., S. Ramasamy, K. Sato, A. Kołodziejczyk & R. Szmigielski (2021), Structural Characterisation of Dimeric Esters in αPinene Secondary Organic Aerosol Using N2 and CO2 Ion Mobility Mass Spectrometry, Atmosphere, 12(1), 17.
Inomata, S. (2021), New Particle Formation Promoted by OH Reactions during α-Pinene Ozonolysis, ACS Earth Space Chem., 5(8),1929-1933, doi:10.1021/acsearthspacechem.1c00142.
Inoue, K.-i., C. Takada, L. Wang, A. Morita & S. Ye (2020), In Situ Monitoring of the Unsaturated Phospholipid Monolayer Oxidationin Ambient Air by HD-SFG Spectroscopy, J. Phys. Chem. B, 124(25), 5246-5250, doi:10.1021/acs.jpcb.0c03408.
Ishiyama, T., A. Morita & T. Miyamae (2011), Surface structure of sulfuric acid solution relevant to sulfate aerosol: molecular
dynamics simulation combined with sum frequency generation measurement, Phys. Chem. Chem. Phys., 13(47), 20965-20973,
doi:10.1039/C1CP21920K.
Ishizuka, S., A. Matsugi, T. Hama & S. Enami (2020), Interfacial Water Mediates Oligomerization Pathways of Monoterpene
Carbocations, J. Phys. Chem. Lett., 11(1), 67-74, doi:10.1021/acs.jpclett.9b03110.
Matsuoka, K., Y. Sakamoto, T. Hama, Y. Kajii & S. Enami (2017), Reactive Uptake of Gaseous Sesquiterpenes on Aqueous Surfaces,
J. Phys. Chem. A, 121, 810－818, doi:10.1021/acs.jpca.6b11821.
Nagashima, K. et al. (2016), Direct Visualization of Quasi-Liquid Layers on Ice Crystal Surfaces Induced by Hydrogen Chloride Gas,
Cryst. Growth Des., 16(4), 2225-2230, doi:10.1021/acs.cgd.6b00044.
Nagashima, K., G. Sazaki, T. Hama, K.-i. Murata & Y. Furukawa (2018), Uptake Mechanism of Atmospheric Hydrogen Chloride Gas
in Ice Crystals via Hydrochloric Acid Droplets, Cryst. Growth Des., 18(7), 4117-4122, doi:10.1021/acs.cgd.8b00531.
Nagata, Y. et al. (2019), The Surface of Ice under Equilibrium and Nonequilibrium Conditions, Acc. Chem. Res., 52(4), 1006-1015,
doi:10.1021/acs.accounts.8b00615.
Negishi, K. & J.-Y. Kohno (2019), Low-Frequency Raman Scattering in Colliding Benzene Droplets, J. Phys. Chem. A, 123(42), 91589165, doi:10.1021/acs.jpca.9b06354.
Nojima, Y., Y. Shioya, H. Torii & S. Yamaguchi (2020), Hydrogen order at the surface of ice Ih revealed by vibrational spectroscopy,
Chem. Commun., 56(33), 4563-4566, doi:10.1039/D0CC00865F.
Nojima, Y., Y. Suzuki & S. Yamaguchi (2017), Weakly Hydrogen-Bonded Water Inside Charged Lipid Monolayer Observed with
Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy, J. Phys. Chem. C, 121(4), 2173-2180,
doi:10.1021/acs.jpcc.6b09229.
Qiu, J., S. Ishizuka, K. Tonokura, A. J. Colussi & S. Enami (2019a), Water Dramatically Accelerates the Decomposition of aHydroxyalkyl-Hydroperoxides in Aerosol Particles, J. Phys. Chem. Lett., 10, 5748-5755.
Qiu, J., S. Ishizuka, K. Tonokura & S. Enami (2019b), Interfacial vs Bulk Ozonolysis of Nerolidol, Environ. Sci. Technol., 53, 5750－
5757, doi:10.1021/acs.est.9b00364.
Qiu, J., Z. Liang, K. Tonokura, A. J. Colussi & S. Enami (2020), Stability of Monoterpene-Derived α- Hydroxyalkyl-Hydroperoxides
in Aqueous Organic Media: Relevance to the Fate of Hydroperoxides in Aerosol Particle Phases, Environ. Sci. Technol., 54(7), 38903899, doi:10.1021/acs.est.9b07497.
Sakamoto, Y. & K. Tonokura (2012), Measurements of the Absorption Line Strength of Hydroperoxyl Radical in the n3 Band using aContinuous Wave Quantum Cascade Laser, J. Phys. Chem. A, 116(1), 215-222, doi:10.1021/jp207477n.
Sakamoto, Y., A. Yabushita, M. Kawasaki & S. Enami (2009), Direct Emission of I2 Molecule and IO Radical from the Heterogeneous
Reactions of Gaseous Ozone with Aqueous Potassium Iodide Solution, J. Phys. Chem. A, 113(27), 7707-7713,
doi:10.1021/jp903486u.
Sazaki, G., S. Zepeda, S. Nakatsubo, E. Yokoyama & Y. Furukawa (2010), Elementary steps at the surface of ice crystals visualized byadvanced optical microscopy, Proc. Natl. Acad. Sci. U. S. A., 107(46), 19702, doi:10.1073/pnas.1008866107.
Sekimoto, K., D. Fukuyama & S. Inomata (2020), Accurate identification of dimers from α-pinene oxidation using high-resolution
collision-induced dissociation mass spectrometry, J. Mass Spectrom., 55(6), e4508, doi:https://doi.org/10.1002/jms.4508.
Shiraiwa, M. et al. (2017), Aerosol health effects from molecular to global scales, Environ. Sci. Technol., 51(23), 13545-13567.
Suzuki, T. & J.-Y. Kohno (2014), Simultaneous Detection of Images and Raman Spectra of Colliding Droplets: Composition Analysis
of Protrusions Emerging during Collisions of Ethanol and Water Droplets, J. Phys. Chem. B, 118(21), 5781-5786,

36doi:10.1021/jp503285w.
Tajiri, T. et al. (2013), A Novel Adiabatic-Expansion-Type Cloud Simulation Chamber, J. Meteor. Soc. Jpn. Ser. II, 91(5), 687-704,
doi:10.2151/jmsj.2013-509.
Takenaka, N. & H. Bandow (2007), Chemical Kinetics of Reactions in the Unfrozen Solution of Ice, J. Phys. Chem. A, 111(36), 87808786, doi:10.1021/jp0738356.
Yajima, R., Y. Sakamoto, S. Inomata & J. Hirokawa (2017), Relative Reactivity Measurements of Stabilized CH2OO, Produced by
Ethene Ozonolysis, Toward Acetic Acid and Water Vapor Using Chemical Ionization Mass Spectrometry, J. Phys. Chem. A, 121(34),6440-6449, doi:10.1021/acs.jpca.7b05065.

37

Table A-4. Summary table for the topic Terrestrial ecosystem and atmospheric chemistry(Authors: Michihiro Mochida, Akihiko Ito, Kazuhide Matsuda, Akira Tani)
1. Ultimate Goals 
2. Progress in the past 10 years:
globaldevelopment andJapaneseuniqueness

3. Current major 
gaps







4. Key questions and hypothesis todrive research anddevelopment
during 2022-32








To understand the dynamics and exchange of long-lived gases, especially greenhouse gases, on a multi-scale
and with high accuracy over the short to long term. To elucidate the mechanisms of changes in the exchange
rates and contribute to impact assessment and planning of adaptation and mitigation measures byquantitatively predicting the budget associated with global environmental changes.
To deepen understanding of deposition and exchange processes of atmospheric substances, to model thephenomena, and to improve the prediction accuracy of chemical transport models.
To elucidate the mechanisms of BVOC emissions and factors influencing them at the molecular, cellular,
tissue, individual, and community levels, and to elucidate the BVOC-mediated effects on air quality andclimate.
To quantify the effects of terrestrial ecosystems on the atmospheric aerosol budget and enable future
projections. To understand them in terms of the climatic effects of aerosols and the relationship between
climate and vegetation.
Dramatic increase in the amount of observation data by ground and satellite, and implementation of integrated
analysis of greenhouse gases. Japan has contributed with highly accurate atmospheric observation data andbudget estimation using atmospheric transport and terrestrial material circulation models. iLEAPS has been
implemented, and interdisciplinary research on air-land material exchange has been revitalized in Japan.
In the beginning of this century, flux observations for various chemical components and deposition surfaces
were conducted using new technologies, and models were validated and compared. The new technologies
have revealed components and surfaces with large uncertainties in deposition rates.
Research on molecular to ecological levels, such as plant-plant communication and environmental responseto release, and the development and widespread use of real-time measurement devices have progressed.
BVOC research on land modification and urban green space progressed in Japan.
Improved understanding of the formation mechanisms of biogenic secondary organic aerosols (BSOA),
including the formation of highly oxidized organic molecules (HOMs) by autoxidation. Advances inbioaerosol research based on molecular tracer analysis and fluorescence measurements. In Japan,
contributions were made to laboratory experiments and field observations related to BSOA.
Large discrepancies in model intercomparison results for greenhouse gases. Severe uncertainties in emission
inventories as well. Monitoring system needs to be expanded to capture changes associated with events thatare difficult to predict.
Discrepancies between theoretical and observed deposition rates, inability to reproduce upward emission
phenomena, and contribution to the refinement of transport and deposition simulations for transboundary air
pollution control.
It is necessary to measure the amount and concentration of BVOC emissions, to develop satellite observation
methods to estimate them, and to develop inexpensive analytical methods. Measurement equipment isexpensive, and this is not a field that young researchers can easily tackle.
Challenges in understanding the amount and characteristics of BSOA production and its representation inatmospheric models. Bioaerosol measurement methods are not well established; resources available for
BSOA observations are not being utilized.
In understanding the material cycles of atmospheric and terrestrial ecosystems and the impact of their changes
on human society, there is a lack of academic knowledge on BVOCs and aerosols, and efforts to link suchknowledge to social implementation are lacking.
The existence of long-term attenuation of CO2 fertilization effects, the impact of future deforestation andfires on the carbon budget, and the impact of air pollutants on greenhouse gas exchange. More sophisticatedobservation and modeling methods are required to provide a consistent explanation of the global budget.
Efforts are needed to provide scientific data for the Global Stocktake of the Paris Agreement.
Acquisition of highly accurate datasets through strategic observations based on flux observations targeting
forests in particular, in collaboration with Asia-Flux and others, will lead to a better understanding of theprocess and improve the accuracy of model predictions.
Development of new measurement and analysis methods for BVOCs and lower cost analytical equipment.
Establishment of an environment for new researchers to enter the field by organizing cross-disciplinarygroups and launching projects in atmospheric chemistry, ecology, plant physiology and ecology, and otherfields.
To deepen our understanding of the BSOA production process and explain the amount and characteristics of
BSOA production; to quantify the impact of BSOA and bioaerosol production on climatic processes and to
determine the presence and extent of feedback mechanisms on vegetation.
A comprehensive understanding of interactions (e.g., GPP promotion and CO2 fixation by nitrogen
deposition) across fields (e.g., CO2, GPP, BVOC, BSOA) will help elucidate undiscovered processes andimprove quantification of the material balance.

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To improve quantitative predictability of the dynamics of total organic matter involving terrestrial
ecosystems, including the effects of human activities.

We will promote research on atmospheric and terrestrial ecosystems for an integrated understanding of the
Earth's surface systems, and based on this, promote social implementation of the same themes.
5. Collaborations  IGAC, GCP, iLEAPS, FLUXNET, iCACGP etc.
Figure A-4. Negative feedback via the BSOA formation.
Selected References (Terrestrial ecosystem and atmospheric chemistry)
Chandra, N., et al. (2021), Emissions form the oil and gas sectors, coal mining and ruminant farming drive methane growth over the past
three decades, J. Meteor. Soc. Jpn., 99, 309‒337, doi:10.2151/jmsj.2021-015.
Deng. Y. et al. (2019), Diurnal variation and size dependence of the hygroscopicity of organic aerosol at a forest site in Wakayama,
Japan: their relationship to CCN concentrations, Atmos. Chem. Phys., 19, 5889‒5903, doi:10.5194/acp-19- 5889-2019.
Fukui, T., K. Kokuryo, T. Baba and A. Kannari (2014), Updating EAGrid2000-Japan emissions inventory based on the recent emission
trends, J. Jpn. Soc. Atmos. Environ., 49, 117-125, doi.org/10.11298/taiki.49.117 (in Japanese).
Itahashi, S. et al. (2020), MICS-Asia III: overview of model intercomparison and evaluation of acid deposition over Asia, Atmos. Chem.
Phys., 20, 2667‒2693, doi:10.5194/acp-20-2667-2020.
Ito, A. (2019), Disequilibrium of terrestrial ecosystem CO2 budget caused by disturbance-induced emissions and non- CO2 carbon export
flows: a global model assessment, Earth Syst. Dynam., 10, 685‒709, doi:10.5194/esd-10-685-2019.
Izuta, T. (Ed.) (2017), Air Pollution Impacts on Plants in East Asia, Springer Tokyo, doi:10.1007/978-4-431-56438-6.
Jung, M., et al. (2020), Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach,
Biogeosciences, 17, 1343‒1365, doi:10.5194/bg-17-1343-2020.
Katata, G., K. Matsuda, A. Sorimachi, M. Kajino & K. Takagi (2020), Effects of aerosol dynamics and gas-particle conversion on dry
deposition of inorganic reactive nitrogen in a temperate forest. Atmos. Chem. Phys., 20, 4933‒4949. doi:10.5194/acp-20-4933-2020.
Kawamiya, M., T. Hajima, K. Tachiiri, S. Watanabe & T. Yokohata (2020), Two decades of Earth system modeling with an emphasis on
Model for Interdisciplinary Research on Climate (MIROC), Prog. Earth Planet. Sci., 7, 64, doi:10.1186/s40645-020-00369-5.
Kokubu Y, S. Hara & A. Tani (2020), Mapping seasonal tree canopy cover and leaf area using Worldview-2/3 satellite imagery: A
megacity-scale case study in Tokyo urban area, Remote Sens., 12, 1505, doi:10.3390/rs12091505.
Kondo, M., et al. (2020), State of the science in reconciling topdown and bottom-up approaches for terrestrial CO2 budget, Global
Change Biol., 26, 1068‒1084, doi:10.1111/gcb.14917.
Kurokawa, J. & T. Ohara (2020), Long-term historical trends in air pollutant emissions in Asia: Regional Emission inventory in ASia
(REAS) version 3. Atmos. Chem. Phys., 20, 12761‒12793. Doi:10.5194/acp-20-12761-2020
Masui N, et al. (2020), Does ozone alter the attractiveness of Japanese white birch leaves to the leaf beetle Agelastica coerulea via
changes in biogenic volatile organic compounds (BVOCs): An examination with the Y-tube test, Forests, 11, 58,
doi:10.3390/f11010058.
Matsuda, K., I. Watanabe, V. Wingpud, P. Theramongkol & T. Ohizumi (2006), Deposition velocity of O3 and SO2 in the dry and wet
season above a tropical forest in northern Thailand, Atmos. Environ., 40, 7557‒7564, doi:10.1016/j.atmosenv.2006.07.003.
Matsuda, K., I. Watanabe, K. Mizukami, S. Ban & A. Takahashi (2015), Dry deposition of PM2.5 sulfate above a hilly forest using relaxed
eddy accumulation, Atmos. Environ., 107, 255‒261, doi:10.1016/j.atmosenv.2015.02.050.

39

Nakahara, A., K. Takagi, A. Sorimachi, G. Katata & K. Matsuda (2019), Enhancement of dry deposition of PM2.5 nitrate in a cooltemperate forest. Atmos. Environ., 212, 136‒141, doi:10.1016/j.atmosenv.2019.05.053.
Niwa, Y. et al. (2021), Estimation of fire-induced carbon emissions from Equatorial Asia in 2015 using in situ aircraft and shipobservations, Atmos. Chem. Phys., 21, 9455‒9473, doi:10.5194/acp-21-9455-2021.
Patra, P. K., et al. (2016), Regional methane emission estimation based on observed atmospheric concentrations (2002‒2012), J. Meteor.
Soc. Jpn., 94, 91‒113, doi: 10.2151/jmsj.2016-006.
Sato, K. et al. (2018), Studying volatility from composition, dilution, and heating measurements of secondary organic aerosols formed
during α-pinene ozonolysis, Atmos. Chem. Phys., 18, 5455‒5466, doi:10.5194/acp-18-5455-2018.
Tani, A. & T. Mochizuki (2021), Review: Exchanges of volatile organic compounds between terrestrial ecosystems and the atmosphere.
J. Agric. Meteorol., 77, 66‒80, doi:10.2480/agrmet.D-20-00025.
Tani, A., S. Tobe & S. Shimizu (2010), Uptake of methacrolein and methyl vinyl ketone by tree saplings and implications for forest
atmosphere, Environ. Sci. Technol., 44, 7096‒ 7101, doi:10.1021/es1017569.
Tsunogai, U. et. al. (2010), Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in Eastern Asia using Δ17O, Atmos.
Chem. Phys., 10, 1809‒1820, doi:10.5194/acp-10-1809-2010.
Tsunogai, U., S. Daita, D. D. Komatsu, F. Nakagawa & A. Tanaka (2011), Quantifying nitrate dynamics in an oligotrophic lake using
Δ17O, Biogeosciences, 8, 687‒702, doi:10.5194/bg-8-687-2011.
Yamaga, S. et al. (2021), Trends of sulfur and nitrogen deposition from 2003 to 2017 in Japanese remote areas, Environ. Pollut., 289,
117842, 10.1016/j.envpol.2021.117842.
Yazaki, K., G. I. Arimura & T. Ohnishi (2017), ʻHiddenʼ terpenoids in plants: their biosynthesis, localization and ecological roles, Plant
Cell Physiol., 58, 1615‒1621, doi:10.1093/pcp/pcx123.
Xu, M., K. Kasahara, A. Sorimachi & K. Matsuda (2021), Nitric acid dry deposition associated with equilibrium shift of ammonium
nitrate above a forest by long-term measurement using relaxed eddy accumulation, Atmos.
Environ., 256, 118454, doi:10.1016/j.atmosenv.2021.118454.
Zhu. C., K. Kawamura, Y. Fukuda, M. Mochida, & Y. Iwamoto (2016), Fungal spores overwhelm biogenic organic aerosols in a
midlatitudinal forest, Atmos. Chem. Phys., 16, 7497‒
7506, doi:10.5194/acp-16-7497-2016.

40

Table A-5. Summary table for the topic Marine ecosystem and atmospheric chemistry(Authors: Akinori Ito, Yuzo Miyazaki, Fumikazu Taketani, Yoko Iwamoto, Yugo Kanaya, Jun Nishioka)
1. Ultimate Goals 

2. Progress in the past 10 years:
globaldevelopment and Japanese
uniqueness
3. Current major 
gaps





4. Key questions and hypothesis todrive research anddevelopment
during 2022-32
5. Collaborations 

Humanity has caused global atmospheric pollution and global warming, and we have entered the era known
as the Anthropocene. It is important to understand the essential aspects of the effects of these anthropogenic
global environmental changes on atmospheric chemistry and terrestrial-ocean ecosystem interactions, as wellas the climate feedbacks caused by these effects, and to evaluate and predict these effects in an integrated
manner. Therefore, the ultimate goal is to "clarify the climatic effects of the interaction between atmospheric
trace elements and marine biological activities and their impacts on marine ecosystems and their climate
feedbacks" during the Anthropocene period by integrating observations, experiments, and numericalmodeling studies.
Integrated studies on marine organisms - atmospheric aerosol chemistry and physical processes - and theireffects on cloud condensation nuclei and ice nuclei evolution have been conducted domestically andinternationally.
Atmospheric chemistry observation data by ships were accumulated in Japan, mainly in the North Pacific
Ocean.
An integrated research system of cross-disciplinary observations and models on the atmosphere-ocean budgetof organic matter, iron, and reactive nitrogen was established.
New information on the composition of oceanic atmospheric aerosols was accumulated through offshore
observations using advanced measurements and analyses, such as isotope analysis and fluorescence analysis.
In the North Pacific subarctic region, knowledge on the distribution and circulation of iron in the interior of
the ocean was accumulated.
The ocean model suggests that combustion-derived iron is more efficient than mineral-derived iron for
nutrient fertilization.
The modeling of the oceanic climate and weather systems is still insufficient in terms of a comprehensive
understanding of the processes and amounts of organic matter supplied from surface seawater to theatmosphere, and their effects on cloud condensation nuclei and ice nuclei evolution, and cloud precipitation
processes.
The understanding of the supply and origin of atmospheric components that affect marine ecosystems in eachocean region is still insufficient.
There is a lack of validation data from integrated shipboard observations synchronizing atmospheric andoceanic parameters and field experiments such as mesocosms in the Arctic Ocean, North Pacific Ocean, IndoPacific Ocean, and South Pacific Ocean.
Lack of understanding of interactions between organic matter and nutrients in the ocean-atmosphereboundary layer.
With global warming, ocean acidification, and changes in nutrient deposition to the ocean, how does thequantity and quality of aerosols and precursors emitted from the ocean to the atmosphere change, and to what
extent do positive or negative climate feedbacks occur via their functions such as cloud condensation and ice
nucleation?
Quantify the response of marine ecosystems (e.g., primary production) to the supply of various nutrients andinhibitors from the atmosphere to the ocean.
Long-term integrated atmospheric and oceanic shipboard observations and modeling studies of atmosphericand oceanic circulation in the Arctic Ocean, North Pacific Ocean, Indian Ocean, and South Pacific Ocean
will be conducted.
We will integrate observations, experiments, and modeling studies of organic matter and nutrients that havebeen conducted separately, not only in atmospheric chemistry but also in oceanography, and develop theminto cross-disciplinary research.
The Oceanographic Society of Japan, Meteorological Society of Japan, Geochemical Society of Japan,
Aerosol Society of Japan, SOLAS, CATCH, BEPSII, GESAMP, GEOTRACES, IMBeR

41

Figure A-5. Schematic diagram of interactions between atmospheric aerosols and marine ecosystems and theirclimate relevance in the Anthropocene.
Selected References (Marine ecosystem and atmospheric chemistry)
Dobashi, T. et al. (2022), Marine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in thesubtropical North Pacific, submitted
Hamasaki, K. et al. (2019), Microbial community dynamics in sea surface microlayer and sea spray aerosols observed in coastal inlets
of Japan, SOLAS Open Science Conference.
Inoue, J., Y. Tobo, F. Taketani & K. Sato (2021), Oceanic supply of ice-nucleating particles and its effect on ice cloud formation: A casestudy in the Arctic Ocean during a cold air outbreak in early winter, Geophys. Res. Lett., 48, e2021GL094646,
doi.org/10.1029/2021GL094646.
Itahashi, S., H. Hayami, I. Uno, X. Pan & M. Uematsu (2016), Importance of coarse-mode nitrate produced via sea salt as atmospheric
input to East Asian oceans, Geophys. Res. Lett., 43, 5483- 5491, doi:10.1002/2016GL068722.
Ito, A. & M. Kawamiya (2010), Potential impact of ocean ecosystem changes due to global warming on marineorganic carbon aerosols, Global Biogeochem. Cycles, 24, GB1012. doi.org/10.1029/2009GB003559.
Ito, A., G. Lin & J. E. Penner (2014), Reconciling modeled and observed atmospheric deposition of soluble organic nitrogen at coastal
locations, Global Biogeochem. Cycles, 28, 617-630, doi.org/10.1002/2013GB004721.
Ito, A. et al. (2019), Pyrogenic iron: The missing link to high iron solubility in aerosols, Sci. Adv., 5, eaau7671,
doi.org/10.1126/sciadv.aau7671.
Ito, A., Y. Ye, A. Yamamoto, M. Watanabe & M. N. Aita (2020a), Responses of ocean biogeochemistry to atmospheric supply of
lithogenic and pyrogenic iron-containing aerosols, Geol. Mag., 157, 741-756, doi.org/10.1017/S0016756819001080.
Ito, A. et al. (2020b), Evaluation of aerosol iron solubility over Australian coastal regions based on inverse modeling: Implications ofbushfires on bioaccessible iron concentrations in the Southern Hemisphere, Prog. Earth Planet. Sci., 7, 42, doi.org/10.1186/s40645020-00357-9.
Ito, A., Y. Ye, C. Baldo & Z. Shi (2021), Ocean fertilization by pyrogenic aerosol iron, npj Clim. Atmos. Sci., 4, 30,
doi.org/10.1038/s41612-021-00185-8.
Iwamoto, Y. et al. (2011), Biogeochemical implications of increased mineral particle concentrations in surface waters of the northwestern
North Pacific during an Asian dust event, Geophys. Res. Lett., 38, L01604, doi.org/10.1029/2010GL045906.
Iwata, A. & A. Matsuki (2018), Characterization of individual ice residual particles by the single droplet freezing method: a case study
in the Asian dust outflow region, Atmos. Chem. Phys., 18, 1785-1804, doi.org/10.5194/acp-18-1785-2018.
Kawai, H. et al. (2019), Significant improvement of cloud representation in the global climate model MRI-ESM2, Geosci. Model Dev.,
12, 2875‒2897, doi.org/10.5194/gmd- 12-2875-2019.
Kawamiya, M., T. Hajima, K. Tachiiri, S. Watanabe & T. Yokohata (2020), Two decades of Earth system modeling with an emphasis on
Model for Interdisciplinary Research on Climate (MIROC). Prog. Earth Planet. Sci., 7, 64, doi.org/10.1186/s40645-020-00369-5.
Kawana, K., K. Matsumoto, F. Taketani, T. Miyakawa & Y. Kanaya (2021), Fluorescent biological aerosol particles over the central
Pacific Ocean: covariation with ocean surface biological activity indicators, Atmos. Chem. Phys. 21, 15969-15983,
doi.org/10.5194/acp-21-15969-2021.

42

Kurisu, M., K. Sakata, M. Uematsu, A. Ito & Y. Takahashi (2021), Contribution of combustion Fe in marine aerosols over thenorthwestern Pacific estimated by Fe stable isotope ratios, Atmos. Chem. Phys., 21, 16027‒16050, doi.org/10.5194/acp-21-160272021.
Kurokawa, J. & T. Ohara (2020), Long-term historical trends in air pollutant emissions in Asia: Regional Emission inventory in ASia
(REAS) version 3, Atmos. Chem. Phys., 20, 12761-12793, doi.org/10.5194/acp-20-12761-2020.
Maki, T. et al. (2018), Long-range-transported bioaerosols captured in snow cover on Mount Tateyama, Japan: impacts of Asian-dust
events on airborne bacterial dynamics relating to ice-nucleation activities, Atmos. Chem. Phys., 18, 8155-8171, doi.org/10.5194/acp18-8155-2018.
Misumi, K. et al. (2021), Slowly sinking particles underlie dissolved iron transport across the Pacific Ocean, Glob. Biogeochem. Cycle,
21115, doi.org/10.1029/2020GB006823.
Miyakawa, T. et al. (2015), Ground-based measurement of fluorescent aerosol particles in Tokyo in the spring of 2013: Potential Impacts
of non-biological materials on autofluorescence measurements of airborne particles, J. Geophys. Res. Atmos. 120, 1171-1185,
doi:10.1002/2014JD022189.
Miyakawa, T. et al. (2022), Shipborne measurements of aerosol particles over the Southern Ocean in the late Austral summer of 2017:
Insights into cloud formation, in preparation.
Miyazaki, Y. et al. (2018), Chemical transfer of dissolved organic matter from surface seawater to sea spray water soluble organic aerosolin the marine atmosphere, Sci. Rep., 8, 14861, doi:10.1038/s41598-018-32864-7.
Miyazaki, Y. et al. (2020), New index of organic mass enrichment in sea spray aerosols linked with senescentstatus in marine phytoplankton, Sci. Rep., 10, 17042, doi:10.1038/s41598-020-73718-5.
Moteki, N. et al. (2017), Anthropogenic iron oxide aerosols enhance atmospheric heating, Nat. Commun., 8, 15329,
doi.org/10.1038/ncomms15329.
Moteki, N. (2020), Capabilities and limitations of the single particle extinction and scattering method for estimating the complex
refractive index and size-distribution of spherical and non-spherical submicron particles, J. Quant. Spectrosc. Radiat. Transfer, 243,
106811, doi.org/10.1016/j.jqsrt.2019.106811.
Moteki, N. (2021), Measuring the complex forward-scattering amplitude of single particles by self-reference interferometry: CAS-v1
protocol, Opt. Express, 29(13), 20688-20714, doi.org/10.1364/OE.423175.
Myriokefalitakis, S. et al. (2018), Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study,
Biogeosciences, 15, 6659-6684, doi.org/10.5194/bg-15-6659-2018.
Nakane, M., T. Ajioka & Y. Yamashita (2017), Distribution and Sources of Dissolved Black Carbon in Surface Waters of the Chukchi
Sea, Bering Sea, and the North Pacific Ocean, Front. Earth Sci., 5, 34, doi: 10.3389/feart.2017.00034.
Nishino, S. et al. (2011), Enhancement/reduction of biological pump depends on ocean circulation in the sea-ice reduction regions of the
Arctic Ocean, J. Oceanogr., 67, 305-314, doi.org/10.1007/s10872-011-0030-7.
Nishioka, J. et al. (2021), A review: iron and nutrient supply in the subarctic Pacific and its impact on phytoplankton production, J.
Oceanogr., 77, 561-587, doi.org/10.1007/s10872-021-00606-5.
Takemura, T., T. Nakajima, A. Higurashi, S. Ohta, & N. Sugimoto (2003), Aerosol distributions and radiative forcing over the Asian
Pacific region simulated by Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS), J. Geophys. Res., 108, 8659,
doi.org/10.1029/2002JD003210.
Taketani, F. et al. (2013), Measurement of fluorescence spectra from atmospheric single submicron particle using laser-induced
fluorescence technique, Journal of Aerosol Science, 58, 1-8, doi.org/10.1016/j.jaerosci.2012.12.002.
Taketani, F. et al. (2018), Seasonal response of north western Pacific marine ecosystems to deposition of atmospheric inorganic nitrogencompounds from East Asia, Sci. Rep., 8(1), 9324, doi.org/10.1038/s41598-018-27523-w.
Tanimoto, H., S. Kameyama, T. Iwata, S. Inomata & Y. Omori (2014), Measurement of air-sea exchange of dimethyl sulfide and acetone
by PTR-MS coupled with gradient flux technique, Environ. Sci. Technol. 2014, 48, 1, 526‒533, doi.org/10.1021/es4032562.
Tobo, Y. (2016), An improved approach for measuring immersion freezing in large droplets over a wide
temperature range, Sci. Rep., 6, 32930, doi:10.1038/srep32930.
Tobo, Y. et al. (2020), Seasonal trends of atmospheric ice nucleating particles over Tokyo, J. Geophys. Res. Atmos., 125, e2020JD033658,
doi.org/10.1029/2020JD033658.
Uetake, J. et al. (2020), Airborne bacteria confirm the pristine nature of the Southern Ocean boundary layer, Proc. Natl. Acad. Sci. USA.,117 (24), 13275-13282, doi.org/ 10.1073/pnas.2000134117.
Yoshizue, M. et al. (2019), Individual particle analysis of marine aerosols collected during the north-south transect cruise in the Pacific
Ocean and its marginal seas, J. Oceanogr., 75, 513-524, doi.org/10.1007/s10872-019-00519-4.
Zhu, C. et al. (2020), Characterization of microplastics on filter substrates based on hyperspectral imaging: laboratory assessments,
Environ. Pollut., 263, 114296, doi.org/10.1016/j.envpol.2020.114296.

43

Table A-6. Summary table for the topic Aerosol-radiation/cloud interactions(Authors: Hitoshi Matsui, Sho Ohata, Yutaka Tobo, Atsushi Matsuki, Syuichi Itahashi, Naga Oshima, Kentaro
Suzuki, Yousuke Sato)
1. Ultimate Goals 
2. Progress in the past 10 years:
globaldevelopment andJapanese
uniqueness

3. Current major 
gaps







4. Key questions and hypothesis todrive research anddevelopment
during 2022-32










The number concentration of aerosols by particle size and total mass concentration by aerosol composition
should be known and predicted.
The aerosol particle and the total aerosol as a whole should be characterized and predicted in terms of opticalproperties, hygroscopicity, cloud condensation nucleus properties, ice nucleating properties, and so on.
The aerosol-radiation interaction and aerosol-cloud interaction processes should be well represented using
numerical models validated and constrained by in-situ and satellite observations, to achieve reliable climate
and environmental impact predictions.
The aerosol composition and physicochemical properties (e.g., hygroscopicity, cloud condensation nucleus
properties, ice crystal nucleating properties, etc.) have been measured and laboratory experiments andatmospheric observation data of various aerosols have been accumulated worldwide. Correspondingly,
numerical models have been improved to represent aerosol properties such as mixing state, hygroscopicity,and cloud condensation nucleation properties, as well as processes such as new particle formation, secondaryorganic aerosol formation, and wet deposition. In Japan, observations and modeling studies have accumulated
knowledge on aerosol emission, transport, chemical transformation, deposition, and other processes, taking
advantage of the country's geographical location downstream from the Asian continent, and have improved
estimates of the effects of transboundary air pollution and radiative forcing of aerosols.
Satellite observations, general circulation climate models, and global cloud-resolving models have developedin an interactive manner, and our understanding of aerosol-cloud interactions has advanced. In satellite
observations, the combined use of active and passive sensors has advanced our observational understandingof cloud response to aerosol perturbations. By utilizing the world's most powerful large computers, such as
the K computer and the Fugaku computer, Japan has led the research on aerosol-cloud interactions using
global cloud-resolving models.
In the latest IPCC 6th Assessment, the range of uncertainties in the estimates of aerosol-radiation interactions
and radiative forcing from aerosol-cloud interactions has not decreased since the 5th Assessment, and thevariability in the estimates among climate models remains large. The variability in estimates among climate
models is still significant. Estimates of the physico-chemical properties and spatio-temporal distribution ofaerosols, which determine these radiative forcings, also continue to show large inter-model variability.
The temporal and spatial distribution of aerosols, especially in the polar regions, the open ocean, and theupper troposphere, is not well understood and reproduced by numerical models. The aerosol dynamics in thepast based on ice core analysis and the validation of numerical models are also insufficient.
The understanding of the atmospheric abundance and dynamics of aerosols that act as ice nucleating particles(INPs) and the mechanisms that form ice crystals is inadequate.
The long-term monitoring stations in Asia, South America, Africa, Oceania, and Siberia are relatively
insufficient compared to those in Europe.
Understanding of the response of cloud/precipitation systems to aerosol perturbations is inadequate. In
particular, it is necessary to understand the response of clouds including ice at the elementary process level.
Model representations of aerosol, cloud, and precipitation processes are not well constrained by observations.
Can the uncertainty ranges in the estimation of radiative forcing from aerosol-radiation interactions andaerosol-cloud interactions be reduced by accumulating field and satellite observation data, integrating
observations and numerical models, and refining and increasing the resolution of numerical models?
Can the knowledge of aerosol processes (mixing state, formation process and hygroscopic properties oforganic aerosols, transformation process of black carbon, emission and formation process of brown carbon,
new particle formation, etc.) obtained from laboratory experiments and observations be appropriately
incorporated into the numerical model?
What kind of surface structure of the INP induces the formation of ice crystals? Can long-term observationsof INP at multiple locations clarify the dynamics of INP? Can we develop new measurement techniques forthis purpose?
Can we establish a sustainable long-term observation network of aerosol optical properties, particle size
distribution, cloud condensation nuclei, INP, and chemical composition in East Asia, including Japan, in
addition to ground-based remote sensing observations?
Can we quantitatively predict future changes in air pollutants? Can the project contribute to the developmentof emission scenarios that enable us to address both air pollution and climate change?
Can we introduce new elements into the numerical model system that are not fully considered in most existing
aerosol models (e.g., ice nucleating properties, composition of mineral dust, bioaerosols, etc.) and clarify
their spatio-temporal distribution and radiative forcing?
Can we estimate and evaluate the interaction between aerosols and climate more quantitatively and

44







5. Collaborations 

comprehensively, including the response of not only anthropogenic aerosols but also naturally occurring
aerosols to climate change?
Can a new satellite observation mission with simultaneous cloud radar, precipitation radar, and lidar elucidate
the interactions between microphysical and dynamical processes that complicate the cloud response toaerosols? How can this combined observational information be used to provide observational diagnostics ofimportant elementary processes in aerosols, clouds, and precipitation?
In general circulation climate models (GCMs), can we elucidate the effects of aerosols on mixed phase
clouds, including ice, and the resulting radiative effects and interactions between convective clouds andaerosols? Can global cloud-resolving models (GCRMs) reproduce past climate conditions and link them toclimate studies, and can aerosol-cloud interactions be studied in global LES models in a seamless mannerthat can be quickly linked to GCRMs?
How can the representation of aerosol, cloud, and precipitation processes in these models be constrained andrefined based on satellite observations?
How can we achieve both high accuracy and high speed in modeling elemental processes by using machinelearning?
Meteorological Society of Japan, The Japanese Society of Snow and Ice, Japan Geoscience Union, Japan
Association of Aerosol Science and Technology, IGAC, ESA-JAXA EarthCARE satellite mission, NASAAOS satellite mission

Figure A-6. (a-c) Seasonal change in the observed and modeled black carbon mass concentrations in the Arctic.
(d-f) Susceptibility of cloud increase per aerosol increase (A-Train, NICAM, GCM(MIROC)). (adopted from
Sato et al. (2016, 2018) and Goto et al. (2020).
Selected References (Aerosol-radiation/cloud interactions)
Aikawa, M. et al. (2010), Significant geographic gradients in particulate sulfate over Japan determined from multiple-sitemeasurements and a chemical transport model: Impacts of transboundary pollution from the Asian continent, Atmos. Environ., 44.
381-391, doi:10.1016/j.atmosenv.2019.10.025.
AMAP, (2021), Impacts of Short-lived Climate Forcers on Arctic Climate, Air Quality, and Human Health. Summary for Policymakers. Arctic Monitoring and Assessment Programme (AMAP), Tromso, Norway. 20 pp
Aoki, T. et al. (2011), Physically based snow albedo model for calculating broadband albedos and the solar heating profile in snowpack
for general circulation models. J. Geophys. Res. Atmos., 116, D11114, doi:10.1029/2010JD015507.
Aoki, T., S. Matoba, J. Uetake, N. Takeuchi & H. Motoyama (2014), Field activities of the “Snow Impurity and Glacial Microbe
effects on abrupt warming in the Arctic” (SIGMA) Project in Greenland in 2011-2013. Bull. Glaciol. Res., 32, 3-20, doi:45

10.5331/bgr.32.3.
Chen, Q., F. Ikemori & M. Mochida (2016), Light absorption and excitation-emission fluorescence of urban organic aerosol
components and their relationship to chemical structure, Environ. Sci. Technol., 50, 10859‒10868, doi:10.1021/acs.est.6b02541.
Eguchi, K. et al. (2011), Modulation of cloud droplets and radiation over the north Pacific by sulfate aerosol erupted from mount
Kilauea. SOLA, 7, 077-080, doi:10.2151/sola.2011-020.
Gen, M., et al. (2019), Electrospray surface-enhanced Raman spectroscopy (ES-SERS) for studying organic coatings of atmosphericaerosol particles. Aerosol. Sci. Tech., 53(7), 760-770, doi.org/10.1080/02786826.2019.1597964.
Glis, J. et al. (2021), AeroCom phase III multi-model evaluation of the aerosol life cycle and optical properties using ground andspace-based remote sensing as well as surface in situ observations. Atmos. Chem. Phys., 21, 87‒128, doi:10.5194/acp-21-87-2021.
Goto, D. et al. (2020), Global aerosol simulations using NICAM.16 on a 14 km grid spacing for a climate study:
improved and remaining issues relative to a lowerresolution model. Geosci. Model Dev., 13(8), 3731‒3768.
Hara, K. et al. (2021), Characterization of aerosol number size distributions and their effect on cloud properties at Syowa Station,
Antarctica, Atmos. Chem. Phys., 21, 12155‒12172, doi.org/10.5194/acp-21-12155-2021.
Hattori, S. et al. (2021), Isotopic evidence for acidity-driven enhancement of sulfate formation after SO2 emission control, Sci. Adv. 7,19, eabd4610, doi:/10.1126/sciadv.abd4610.
Higurashi, A. & T. Nakajima (1999), Development of a two-channel aerosol retrieval algorithm on a global scale using NOAAAVHRR. J. Atmos. Sci., 56, 924-941.
Iizuka, Y. et al., (2018), A 60 year record of atmospheric aerosol depositions preserved in a high-accumulation dome ice core,Southeast Greenland. J. Geophys. Res. Atmos., 123, doi:/10.1002/2017JD026733.
Ikeda, K. & H. Tanimoto (2015), Exceedances of air quality standard level of PM2.5 in Japan caused by Siberian wildfires, Env. Res.
Lett., 10, 105001, doi: 10.1088/1748- 9326/10/10/105001.
Inoue, J., Y. Tobo, F. Taketani & K. Sato (2021), Oceanic supply of ice-nucleating particles and its effect on ice cloud formation: A
case study in the Arctic Ocean during a cold air outbreak in early winter, Geophys. Res. Lett., 48, e2021GL094646.
Isono, K., M. Komabayashi & A. Ono (1959), The nature and the origin of ice nuclei in the Atmosphere, J. Meteorol. Soc. Jpn., 37,
211-233.
Isono, K. & T. Tanaka (1966), Sudden increase of ice nucleus concentration associated with thunderstorm, J. Meteorol. Soc. Jpn., 44,
255-259.
Itahashi et al. (2018), A 15-year record (2001-2015) of the ratio of nitrate to non-sea-salt sulfate in precipitation over East Asia, Atmos.
Chem. Phys., 18. 2835-2852, doi:10.5194/acp-18-2835-2018.
Ito, A., G. Lin & J. E. Penner (2018), Radiative forcing by light absorbing aerosols of pyrogenetic iron oxides. Sci. Rep. 8, 7347,
doi:10.1038/s41598-018-25756-3.
Ito, A. et al. (2019), Pyrogenic iron: The missing link to high iron solubility in aerosols, Sci. Adv., 5, eaau7671,
doi:10.1126/sciadv.aau7671.
Ito, A. et al. (2021), Ocean fertilization by pyrogenic aerosol iron, npj Clim. Atmos. Sci., 4, doi:10.1038/s41612-021-00185-8.
Iwamoto, Y. et al. (2021), Aerosol-Cloud Interaction at the Summit of Mt. Fuji, Japan: Factors Influencing Cloud
Droplet Number Concentrations, Appl. Sci., 11, 8439, doi.org/10.3390/app11188439.
Jones, C. D., et al. (2021), The climate response to emissions reductions due to COVID-19: Initial results from CovidMIP. Geophys.
Res. Lett., 48, e2020GL091883, doi:10.1029/2020GL091883.
Kanaya, Y. et al. (2020), Rapid reduction in black carbon emissions from China: evidence from 2009‒2019 observations on Fukue
Island, Japan, Atmos. Chem. Phys., 20, 6339‒6356, doi:/10.5194/acp-20-6339-2020.
Kaneyasu, N. et al. (2014), Impact of long-range transport of aerosols on the PM2. 5 composition at a major metropolitan area in thenorthern Kyushu area of Japan. Atmos. Environ., 97, 416-425.
Kawai, K., H. Matsui & Y. Tobo (2021), High potential of Asian dust to act as ice nucleating particles in mixed-phase clouds simulatedwith a global aerosol-climate model, J. Geophys. Res. Atmos., 126, e2020JD034263.
Kawamoto, K., T. Nakajima & T. Y. Nakajima (2001), A global determination of cloud microphysics with AVHRR remote sensing. J.
Climate, 14, 2054-2068.
Kinase, T. et al. (2020), Concentrations and size distributions of black carbon in the surface snow of eastern Antarctica in 2011, J.
Geophys. Res. Atmos., 125, e2019JD030737, doi:/10.1029/2019JD030737.
Kobayashi, H. et al. (2014), Development of a polarization optical particle counter capable of aerosol type classification, Atmos.
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46

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Table A-7. Summary table for the topic Stratosphere and Mesosphere(Authors: Nawo Eguchi, Yosuke Yamashita, Hideharu Akiyoshi, Tetsu Sakai, Tomoo Nagahama, Yoshihiro
Tomikawa, Hideaki Nakajima, Takafumi Sugita, Takatoshi Sakazaki, Takuya Saito, Akira Mizuno)
1. Ultimate Goals 






2. Progress in the past 10 years:
global
development andJapaneseuniqueness







3. Current major 
gaps





4. Key questions and hypothesis todrive research and 
development
during 2022-32

5. Collaborations 

Understanding of the structure of the boundary region between the troposphere and stratosphere and therelationship between troposphere-stratosphere dynamical coupling and mass exchange.
Understanding of the effects of changes in trace constituents (GHGs, ozone, CFC substitutes, water vapor,etc.) on atmospheric circulation in the stratosphere.
Understanding of ozone layer changes associated with climate change and the impact of ozone layer changes
on climate.
Understanding of the chemical effects of stratospheric aerosols from volcanic eruptions and large forest fires,and quantitative understanding of the contribution of anthropogenic aerosols to the stratosphere and theirinflux processes.
Prediction of the impact of geoengineering to modify the stratospheric aerosol layer as a countermeasureagainst global warming and appropriate indicators based on such predictions.
Understanding of the effects of solar activity (radiation and energetic particles) and magnetosphericphenomena that produce NOx and HOx through ion chemistry and alter mesospheric and stratospheric ozone,
and their impact on climate.
Japan has made valuable contributions to balloon observations in the tropics, such as SOWER, large
atmospheric radars (Indonesia, PANSY in Antarctica), and UTLS region observations with CONTRAIL.
Advancement of numerical models. Improved parameterization of cumulus clouds and gravity waves.
Contribution to the refinement of UTLS processes by chemical transport models.
Improvement of resolution with the development of computer resources.
Increased use of numerical models to study the effects of the ozone layer on the climate, where the ozone
distribution is calculated online in a chemical climate model rather than given.
Japan's SMILES, equipped with the world's first superconducting detector operated by a mechanicalcryogenic refrigerator and observing in a solar asynchronous orbit unrestricted by local time, produced
unique results, including the discovery of diurnal changes in ozone and variations associated with solar
eclipses.
The super-pressure balloon enables in-situ stratospheric observations at about the same altitude for about one
month.
Ground-based FTIR has increased the number of studies that investigate global secular changes by globallyunifying and optimizing analysis tools and molecular parameters. Column quantities can now be derived forabsorption lines such as CFC and HFC, which have weak intensities.
Microwave observations, both ground-based and satellite-based, provide data in the mesosphere and beyond,which is difficult to obtain with other instruments. Japan has advanced technology in the development ofsuperconducting receivers with ultra-high sensitivity for SMILES and other ground-based radiometers.
The temporal and vertical resolutions of current observational data and models are insufficient forunderstanding the material circulation and interactions in the troposphere-stratosphere (-mesosphere). High
resolution observations and models are needed to understand phenomena such as tropical cumulus convection
and tropopause folding, which are small in scale but also important for mass transport.
In order to refine future projections, it is necessary to understand the interactions between meteorologicalfields and trace constituents such as ozone, and to incorporate them appropriately into high-resolution
chemical climate models.
The global satellite program has been stagnant (i.e., plans for continuing missions have been delayed), which
may limit the continuity of global data and the types of trace constituents that can be observed. This mayhinder our understanding of long-term trends in trace constituent concentrations, understanding of transport
processes (consistent with meteorological fields and transport of various trace constituents), and estimationof abundances of equivalent effective stratospheric chlorine (EESC), reactive nitrogen oxides (NOy), etc.
How do trace elements, especially short-lived chemical species, enter the stratosphere from the troposphere?
What are the timescales and troposphere-stratosphere exchange time constants?
How does the stratospheric temperature structure change as the influx of chemical species such as water
vapor from the troposphere to the stratosphere (and vice versa) changes with increasing GHGs?
Basically, the stratospheric cooling effect of increased CO2 will continue to dominate, but it is possible that,
contrary to international regulations, increased concentrations of HFCs and other species may act to increase
temperatures in the lower stratosphere, partially reducing the cooling effect. What will be the atmosphericcirculation in the mid- and high latitudes due to these changes in the temperature structure?
To what extent do solar activity, magnetospheric activity, cosmic rays, and other energy inputs to the Earth's
atmosphere affect the global environment? Do such effects propagate to the troposphere?
SPARC, NDACC, SCOSTEP

50

Figure A-7. Schematic diagram of phenomena and mechanisms relevant to atmospheric chemistry in thestratosphere and mesosphere.
Selected References (Stratosphere and Mesosphere)
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