In celebration of Women’s History Month, this article continues a series of interviews with NOAA Research employees and scientists. NOAA Global Monitoring Laboratory Science Communications Specialist Xinyi Zeng conducted this interview.
Lei Hu is a researcher at CIRES and works in the Halocarbons and Other Trace Species Division of NOAA’s Global Monitoring Laboratory and the Carbon Cycle and Greenhouse Gases Division in Boulder, Colorado.
In his research, Lei uses worldwide atmospheric observations and inverse modeling to quantify regional emissions and removals of greenhouse gases. These observation-based emission estimates help cross-check inventory-based anthropogenic emissions estimates and also provide insight into how natural ecosystems absorb greenhouse gases from the atmosphere to mitigate the greenhouse effect on the climate.
Additionally, some of Lei’s research focuses on ozone-depleting substances and their substitutes, which are also potent greenhouse gases. His work on ozone-depleting substances not only tracks potential violations of the Montreal Protocol on Substances that Deplete the Ozone Layer, but also examines the climate implications of transitioning from ozone-depleting substances to their substitutes.
His journey as a scientist began with a major in chemistry at Ocean University of China. She then moved to the United States for her doctorate. in oceanography from Texas A&M University. She started her career at NOAA 10 years ago as a post-doc at the NOAA Global Monitoring Laboratory and has worked as a researcher at CIRES since her post-doc. Some of his earlier work has been funded by NOAA’s Climate Program Office.
Our conversation follows.
What attracts you to your current field of study?
At first, I just thought it would be cool to work as a scientist in a research institution. I didn’t really know what field of research I should pursue when I was at university.
My undergraduate supervisor studied nitrous oxide, a greenhouse gas, and looked at the amount emitted by the ocean. In his marine biogeochemistry lab, I first heard about trace gases. Based on my undergraduate experience, I applied for a PhD. in the United States and continues to study trace gas emissions from the ocean at Texas A&M University.
In the Earth’s atmosphere, all gases other than nitrogen, oxygen and argon are trace gases. They represent only less than 0.1% of the air in the atmosphere but have significant impacts on our living environment. These include what we commonly call greenhouse gases and ozone depleting substances. During my PhD. studies, my research focused on marine emissions of ozone depleting substances – methyl bromide and methyl chloride.
Another great part of my Ph.D. The research involved measuring the amount of methane emitted from deep-sea gas hydrates from the Deepwater Horizon oil spill and natural gas hydrate seeps. This experience led me to become more interested in research on greenhouse gases.
How is your current research related to your PhD? work and how do they differ from each other?
Quantification of trace gas emissions and their response to climate change across a large landscape is extremely important but quite challenging from local, short-term trace gas measurements. My Ph.D. work examines emissions using short-term trace gas measurements made on a ship. Each measurement only represents emissions on a scale smaller than a few hundred square meters. Understanding emissions from a larger landscape has typically required hundreds of thousands of measurements. Even so, it is difficult to fully characterize the temporal variability and trend of emissions.
What I do now still focuses on broadcasts but looks at a much broader landscape, usually on a national or continental scale. This requires not only atmospheric measurements, but also inverse modeling that derives emissions from atmospheric measurements. Interested in studying larger scale emissions estimates, I came to NOAA’s Global Monitoring Laboratory to learn more about inverse models.
Another difference is the trace gas I am studying. My PhD my work focuses more on ozone depleting chemicals and now my work has shifted more towards greenhouse gases and the carbon cycle. Climate is a very important subject and I believe it is very important to understand greenhouse gas emissions.
What were the challenges you had to face at the start of your research career?
When I started my post-doctorate, I had to learn quickly, but in depth, how inverse modeling works. Also, there was no existing common code that I could work with. So I had to translate my mathematical understanding of inverse modeling into computer code. It all had to start from scratch.
After developing the code, I had to test the code extensively to ensure that it worked properly and that the algorithms took full advantage of the atmospheric measurements we had. I got a lot of support from other senior scientists in the lab who helped answer my questions, but it was still a difficult process.
It took me about three years to develop the model and it kept me from being very productive in publishing during my post-doc. However, now that I’ve developed the model, I have a tool ready to explore the data we’ve collected around the world and explore scientific questions. It is very rewarding.
What areas of research do you plan to focus on in the near future?
I want to focus on three main areas.
The first thing is to provide timely estimates of observation-based greenhouse gas emissions in the United States. In the United States, greenhouse gas emissions from human activities are estimated in the inventory each year based on activities reported to the United States Environmental Protection Agency (EPA). Observation-based emission estimates provide an objective assessment of EPA-reported values and can help evaluate the effectiveness of emission reduction practices.
Second, I want to better understand how plant communities respond to climate change. In my previous work, the combination of carbon dioxide and carbonyl sulfide revealed critical information about how Arctic plant communities are responding to climate change. I want to explore the use of the two trace gases in other regions.
Finally, I am interested in integrating satellite data into our existing regional modeling framework. Our current model only uses in situ measurements of trace gases. However, in situ measurements are sparse in nature, while satellite data, although containing some biases and weaker signals from surface emissions, have higher sampling density and wider sampling coverage. The combination of in situ and satellite observations could potentially help us better quantify greenhouse gas emissions.