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VOICE No. 33


Kengo Sudo

Graduate School of Environmental Studies

My favorite saying: Knowledge breeds doubt, and doubt breeds knowledge


Q: Why did you choose this saying?

This saying was coined by Dr. Torahiko Terada, a physicist and geophysicist I respect. In modern science, where each field is highly subdivided and specialized, we tend to largely neglect to think about things outside our own narrow fields, instead leaving it to its experts. However, my research field — global environment and global warming — has a strong connection with society, and as a scientist, I feel a great sense of responsibility. So any time I come across any sort of information or findings, not only in earth science but also in a wide range of other fields, I first question it, and I try to investigate it and think about it as much as time allows. That's why I have made this is my motto.


Q: What kind of research are you doing?

I develop a chemistry-climate model by introducing simulations of airborne gases and particulates (aerosols) and relevant chemical reactions into climate models, which are numerical models that predict climate change. The chemistry-climate model can calculate changes in global distributions of not only greenhouse gases (ozone, methane, etc.) in the stratosphere and troposphere, but also aerosols like PM2.5, and can also calculate the impacts of these gases and aerosols on the climate.


Using these models, we assess and predict air pollution, air quality, and climate change mechanisms simultaneously, on a hemispheric to global scale. We are also focusing on formulating and proposing measures other than carbon emission reductions that can mitigate global warming by controlling emissions and concentrations of short-lived climate forcers (SLCFs), such as methane, ozone, and aerosols. Recently, we have been working to predict and solve air pollution and climate change problems, especially by using hydroxyl radicals (a molecule that controls the air cleaning and oxidation capacity of the atmosphere).




 Explaining simulation results in his laboratory server room





A global simulation of climate forcing agents as shown

by the chemistry-climate model CHASER (MIROC):

Black carbon on the Earth's surface (upper left),

tropospheric column ozone (upper right), and

OH radical concentrations on the Earth's surface (bottom)




Q: How did you get into this research?

I clearly remember that when I was in kindergarten, I dreamed of becoming a garbage collector, because I liked garbage collection trucks very much. Later, although my dreams shifted to medicine and then to aeronautics, my interest in becoming a science researcher or engineer remained unchanged. When I was in high school, I saw on TV the view of the Earth's surface (lands, oceans, sky, and clouds) from the space shuttle. I was fascinated by its beauty and wonder, which renewed my determination to work in a field related to the Earth. And so, in university, I entered the field of earth science and geophysics. In graduate school, as a first-year master's student, I started working on the chemistry-climate model I mentioned earlier, and its development progressed quite smoothly. There's also the fact that I am not the kind of person who enjoys working under someone else's command. After I took all of these things into consideration, I decided to enroll in the doctoral course, which led me to the job that I am doing now.


Q: What sorts of things make you think that research is interesting or rewarding?

The focal point of my research is simulations, so when a numerical model I designed successfully reproduces the observed data, I feel a great sense of satisfaction that borders on pleasure. (This is similar to the feeling you get when you show off your best imitation of someone and everyone praises you for your performance (laughs).)


Also, with numerical models, we can tease apart multiple phenomena and consider them individually. For example, we can investigate how much of a pollutant in a certain place originated from which sources, or what kinds of mechanisms are involved to what degree in which observed changes. Considering phenomena in this way, I occasionally marvel at the ingenuity of Mother Nature.


Another interesting aspect is that combining numerical models with all our observations and some theoretical calculations can lead to solutions that could never be achieved by any individual method. I think the true joy of my research is that we can enjoy both the engineering side, namely developing models, and the scientific side, namely elucidating phenomena.


Q: In June 2021, your research team released a study* showing that the amount of nitrogen oxide (NOx) emitted from factories and vehicles decreased during the worldwide COVID-19 lockdowns. Tell us more about this study. What can we expect from this finding? Is there something about this research that left an impression on you?

As you know, during the worldwide lockdowns instituted in response to the COVID-19 pandemic in 2020, exhaust gases from vehicles and factories decreased, which led to a dramatic decrease in air pollution. In our study, we focused on NOx. By using a data assimilation method that combines chemistry-climate models (mentioned above) with satellite observations, we were able to produce highly accurate estimates of NOx emission reductions during the lockdowns. Moreover, we also succeeded in empirically illustrating how tropospheric ozone responded to the NOx reductions. Tropospheric ozone is one of the most impactful greenhouse gases, so decreasing tropospheric ozone concentrations by reducing NOx emissions holds promise as an effective means to mitigate global warming. In this sense, it is significant that our analysis demonstrated the degree to which we can expect NOx emission reductions to curb ozone levels. Furthermore, NOx has a large influence on the hydroxyl radical, which determines the oxidation capacity of air, so it may also be linked to the rapid increase in methane starting in 2020. This is the focus of our current study.

*The paper, "Global tropospheric ozone responses to reduced NOx emissions linked to the COVID-19 worldwide lockdowns," was published in the journal Science Advances at


Q: How do you spend your days off? What do you do to recharge?

On my days off, I am usually busy cleaning the house, collecting garbage (my childhood dream has come true! (laughs)), playing with my children and taking them to and from their lessons, and taking care of our bird (parakeet), medaka fish, and goldfish. It can be tiring to try to keep up with children and animals, but it also revitalizes me and keeps me young. I’m also a bit obsessed with air purifiers and I dabble in DIY — I suppose you could say that "improving the environment" is my life’s work.






Q: Please tell us about an experience that you can only talk about now.

I lived with my parents in Tokyo until I got my job at Nagoya University, meaning that the first time I lived alone was when I came here to Nagoya. In the beginning, there were a lot of things about Nagoya and Nagoya University that made me feel overwhelmed! More than 15 years have passed since then, and I've become used to life here. Now, the only miso soup I can eat is the type made from reddish-brown miso (one of the region's local specialties). I've also made myself home here at the Higashiyama Campus. One of the students in the first graduate school course I taught after starting my career at Nagoya University was the woman who is now my wife. She works as a researcher here while taking care of our children and supporting me in many ways. I cannot thank her enough.   


Q: What are your goals and ambitions for the future?

I want to hold true to my personal policy of not doing what other people do. My research field has politically charged aspects, including global warming and environmental issues. While I am somewhat influenced by these aspects, I hope I can rigorously pursue atmospheric and climate science from a phenomenological perspective and stick to my spirit of "also seeing the forest for the trees." When I'm exhausted, though, I do (in the words of comedian Junji Takada) fail to see both the forest and the trees.




 At his Atmospheric Environment & Climate Modeling Laboratory (March 2022)





A social event with members of his laboratory (December 2019)



Name: Kengo Sudo

Department: Graduate School of Environmental Studies

Title: Professor



He attended the University of Tokyo, where he graduated from the Department of Earth and Planetary Science at the Faculty of Science and the Graduate School of Science, ultimately earning his doctorate in science. He worked as a researcher at the Frontier Research System for Global Change and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). In 2006, he became an associate professor at the Graduate School of Environmental Studies at Nagoya University before ascending to his current position in 2019. He is also a Visiting Principal Researcher at JAMSTEC.

In his free time, he likes to clean, drink, watch YouTube videos, sing karaoke, and cut his own hair.