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Arthur Sedlacek

Ogochukwu Enekwizu with a suite of instruments at Brookhaven National Laboratory to make and study soot-seeded clouds. Photo courtesy of BNL

By Daniel Dunaief

Combining forces to form a three-part team, they strive to understand processes that are as visually stunning and inspirational as they are complex and elusive.

Clouds, which are so important to weather and climate, are challenging to understand and predict, as numerous processes affect properties at a range of scales.

A team from Brookhaven National Laboratory has provided the atmospheric sciences community with a host of information that advances an understanding of clouds.

In the atmospheric sciences community, “we typically talk about the three legs of a stool: modeling/ theory; field measurements; and targeted laboratory studies,” explained Arthur Sedlacek, Chemist in the Environmental and Climate Science Department.

Sedlacek conducts field experiments by collecting air samples from clouds in a range of locations such as flying through wildfire plumes.

In the beginning of 2021, BNL added postdoctoral researcher Ogochukwu Enekwizu to bolster another leg of that stool. Enekwizu conducts the kind of laboratory studies that provide important feedback and data for the work of Sedlacek and cloud modelers like Nicole Riemer, Professor in the Department of Atmospheric Sciences at the University of Illinois-Urbana Champaign.

Enekwizu studies how soot aerosols from wildfires influence the lifetime and formation of clouds. She’s also investigating how soot-cloud interactions affect the absorption and scattering of light by soot particles.

Wildfires provide kindling for the climate, as fires release warming agents that contribute to increases in global temperatures which result in more wildfires. By determining how these smaller scale processes in soot affect clouds, Enekwizu can reduce the so-called error bars or level of uncertainty in the models other scientists create and that rely on the data she develops.

Enekwizu’s collaborators appreciate her contribution. As a modeler, Riemer suggested that Enekwizu’s work provided key information.

“While the microscale processes of soot restructure are incredibly complicated, [Enekwizu] was able to boil it down to a few simple parameters,” Riemer explained. “This makes it feasible to implement this process in a model like ours, which look at aerosol populations, not just a few individual particles. From there, we can come up with ways to implement this knowledge into climate models, which are still much more simplified than the model that we are developing.”

Sedlacek, who is her supervisor, suggested that Enekwizu’s work is “now on the cusp of answering important questions of how aerosols interact with clouds.” He descried her set up as “truly unique” and expects her results to inform the community about wildfire aerosol-cloud interactions and will offer guidance on other necessary field measurements.

In broader research terms, wildfires can be important for the ecosystem, as they remove decaying material, clear out underbrush, release nutrients back into the soil and aid the germination of seedlings

The increasing frequency, duration and intensity of these fires has been important to the scientific community. The general public has become increasingly aware of its importance as well, Enekwizu said.


Recruited to BNL by Sedlacek and Atmospheric Scientist Ernie Lewis, Enekwizu is considering collaborations with other researchers at BNL.

She has started speaking with scientists at the Center for Functional Nanomaterials about exploring soot microstructure in a planned joint collaboration with her New Jersey Institute of Technology PhD advisor Dr. Alexie Khakizov. For this effort, Enekwizu has been in discussions with Dmitri Zakharov, who is in charge of the environmental transmission electron microscope at the CFN.

She hopes to take samples and introduces forces under a controlled environment in the transmission electron microscope to see how that affects the structure of soot in fine detail.

Looking at the news with one wildfire event after another, Enekwizu feels compelled to conduct research in the lab and share data amid “a heightened sense of urgency to get this work done” and to share it with the world at large.

Scientific origins

Born in the southeastern part of Nigeria in Enugu and raised in Enugu, Lagos and Abuja, Enekwizu developed an interest in science at 13. She enjoyed classes in a range of sciences and said chemistry was her favorite.

“I knew I was not going to go into medicine because I was squeamish,” she said.

Chemical engineering fascinated her and also appeared to offer career opportunities.

During a chemical engineering internship, she worked at the Nigerian National Petroleum Corporation where she learned about flaring practices. It inspired her final year project on biogas as a renewable energy source and sparked her curiosity on the fate of pollutants and particulate matter that arise from legal and illegal flaring activities. 

In flaring, companies burn off excess gas to control pressure variations, increasing the safety of the operation at the expense of burning a potential resource.

When Enekwizu was at NJIT, Lewis, who is a longtime collaborator with Sedlacek, reached out to Khakizov to inquire about someone with a background in carbonaceous aerosols. After interviewing with Lewis, Sedlacek and others, Enekwizu received the job offer and began working in January of 2021.

A resident of Ridge, Enekwizu, who goes by the name “Ogo,” enjoys festivals and events around Long Island. She also appreciates the area’s ubiquitous beaches and has delighted in strawberry picking.

She hopes to explore Montauk later this spring or summer.


Enekwizu is passionate about mentoring students, particularly those who might be under represented in the field of Science, Technology, Engineering and Medicine.

She served as a graduate student mentor for Divyjot Singh, who was an undergrad at NJIT. Enekwizu taught Singh, who had grown up in Bhopal, India and had only been in the United States for six months when they met, “how to come up with research questions, how to develop hypotheses, how to write a proposal, how to make good presentations for conferences and everything in between,” he explained in an email.

While working with her, Singh found his passion for research and decided to pursue a PhD. 

Enekwizu is also passionate about supporting young women in science. She suggested that young black girls sometimes feel intimidated by STEM classes and careers. She urges a hands on approach to teaching and hopes to be a role model.

“If young girls see people like me thrive in STEM, they’ll be encouraged not to give up,” she said. “That is a huge win, in my opinion.”

By Daniel Dunaief

Two researchers from Brookhaven National Laboratory were stuck on a ship trapped in ice near the North Pole — and they couldn’t have been happier.

In fact, one of them, Matt Boyer, an Atmospheric Scientist at BNL, is returning to the German ship Polarstern for six of the next seven months. The Polarstern is part of a 20-nation effort that will gather information about the Arctic to understand climate change. The scientific collaboration, called MOSAiC (Multidisciplinary Drifting Observatory for the Study of Arctic Climate), started in September and will involve collecting data for a full year.

The scientists are measuring aerosols, cloud particles, and other data through conditions that are among the most challenging on the planet. Researchers aboard the Polarstern regularly endure cold temperatures, fierce winds, minimal to no sunlight and the threat of polar bears unafraid of humans.

Janek Uin, an Associate Atmospheric Scientist at BNL, is working with instruments that measure properties of atmospheric aerosol particles such as their size, the concentration of particles per unit volume of air, how the particles are affected by water vapor and how much light the particles scatter, which affects the sunlight that reaches the Earth’s surface.

Arthur Sedlacek, an atmospheric chemist with the Environmental & Climate Sciences Department at BNL, is one of a host of scientists collecting data from the Polarstern. Indeed, Sedlacek traveled to Tromsø Norway when the ship departed, where he prepared to measure the accumulation of black carbon in the Arctic. 

Caused by burning fossil fuels, emissions from distant wildfires, among other things, black carbon can cause polar ice to melt. When there is sun, the black carbon prevents the reflection of the light, which further darkens the white surface, either through exposure of the underlying ground or previously deposited black carbon.

Sedlacek, who did not travel aboard the Polarstern, said scientists around the world are “itching to see the data” from this ambitious mission. The data collection is “so unique and so important that it will not only help us better understand the current (pristine) state of the cryosphere, but it will also [allow scientists] to better understand (and quantify) how the Arctic is responding to climate change.”

Uin, who is an instrument mentor for about 30 instruments worldwide, recalled how he went out for a fire drill. Following his designated path and waiting for the signal to return, Uin decided to snap some pictures of a frozen and uneven landscape that appeared blue during much of the day, when the faint rays of the sun barely made it over the horizon. Unable to maneuver the camera to his satisfaction, Uin took off his gloves. His exposed fingers became numb in the wind. After he put his gloves back on, it took about 10 minutes for the feeling to return to his hands.

Boyer, meanwhile, who spent more of his time working outside than Uin, helped set up the meteorological site about 1 kilometer away from the ship and is monitoring the size and concentration of organic and inorganic aerosol particles.

The size and concentration of the particles determines how they behave in atmospheric processes, Boyer explained. The size of the particle influences its light scattering ability, how long it stays in the atmosphere, the human health impact and its ability to form clouds, among other properties.

The process of working near the North Pole requires a high level of patience. A task that might take two hours in a lab, for example, might require as long as four days to complete in Arctic conditions.

Boyer described how the moisture from his own breath sometimes froze in his face. “I prefer not to wear goggles” because they fog up, he explained. When he exhaled, the water vapor in his breath caused his eyelids to freeze shut. “You have to constantly close your eyes and pull the ice off your eyelids.”

Boyer had to hold onto a piece of metal when it was well below 0 degrees Fahrenheit and windy. Placing the bolts, nuts and screws into a hole with a glove on is “almost impossible,” Boyer said, although once those items are in place, holding a wrench with gloves on is manageable

Each time people work outside, polar bear guards constantly watch the horizon to make sure the carnivorous creatures don’t approach scientists. While the ship is not a cruise vessel, it offers pleasant amenities, including a small pool, a sauna, an exercise room and nourishment Uin and Boyer, who were roommates aboard the Polarstern, appreciated.

“The food was excellent,” Uin said. “Working long hours in extreme conditions in close quarters, the food has to be good. If it’s bad, morale plummets.” The scientist has been on three ice breakers and the food has always been high quality. 

Uin appreciated the opportunity to take the journey and to conduct the scientific research. “I am reminded how lucky I am that people trust me to do this,” he said.

Uin enjoys the opportunity to look at the ice, which appears blue because of the low light. “People think it’s all white,” he said. “There’s a constant twilight and an all-encompassing blue.” He is excited to look at the information the instruments collect and is “certain that the data will help to bring new insights into the very complex processes governing Earth’s climate and help better predict future trends.”

Boyer, who plans to leave BNL this month to pursue his PhD at the University of Helsinki, said he appreciated the opportunity to be a part of a multi-national team. “I’m one of the luckier people on the planet,” Boyer said. “Not many people will see the Arctic and the Antarctic and I’ve seen both,” adding that there is a satisfaction at being involved with something that is “much larger than myself. I’m a part of a community that works together towards a common goal. It’s nice to be a part of an international team working with people from places and countries who put aside their differences.”

All photos from Janek Uin

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An image from the Biomass Burn Observation Project. Photo from Arthur Sedlacek

The search for small particles has taken Arthur Sedlacek to places like thick plumes of smoke above wildfires raging in the western United States to picturesque vistas on Ascension Island, a staging area for the Allies for antisubmarine activities during World War II.

A chemist in the Environmental and Climate Sciences Department at Brookhaven National Laboratory, Sedlacek is studying aerosols, which are tiny particles suspended in the atmosphere. These particles can form the nuclei of clouds. Depending on their color, they can also either heat or cool the atmosphere.

“White” aerosols, as Sedlacek put it, such as sulfate- or nitrate-based particles, reflect solar radiation, while “black” aerosols, such as soot, absorb the sun’s light and help trap that energy in the atmosphere. By absorbing heat, darker aerosols increase the temperature, while lighter particles reflect some of that heat back into space.

“When you talk about climate change, you identify greenhouse gases, most notably carbon dioxide, which is responsible for warming,” Sedlacek said. “When you run through the model calculations, the models overpredict what we should see. Either something is wrong with the models or something else is counterbalancing the warming effect.”

Arthur Sedlacek photo from Sedlacek
Arthur Sedlacek photo from Sedlacek

Indeed, aerosols represent part of that something else. “We need to incorporate them into our models to better understand what we actually observe in the field,” Sedlacek said. He studies the types of particles, how they age, their color, changes in their color and whether they can act as cloud condensation nuclei.

“We want to understand what’s being produced and how it changes as the plume dilutes and gets older,” Sedlacek said. “How this aging alters the microphysical and optical [properties are] very important to quantifying the contribution of aerosol to climate change.”

During the summer and fall of 2013, Sedlacek was a part of a study called the Biomass Burn Observation Project, which included 14 scientists from seven institutions. Other BNL scientists included his co-principal investigator and chemist Larry Kleinman, atmospheric scientist Ernie Lewis, chemist Stephen Springston and tenured scientist Jian Wang.

Sedlacek spent several hours preparing the equipment that would gather data above these raging fires.

The planes flew into the smoke and then moved in the direction of the smoke, measuring the changes in these aerosols an hour, two hours and more away from the fire. These measurements showed how these aerosols changed over time.

While the study was conducted several years ago, Sedlacek and his colleagues are still working to put together the information.

They have learned that the particles in the air change dramatically in the first few hours. Biomass burning events produce aerosols that are considered “brown carbon” because they are not black, like soot, but they aren’t white like a sulfate- or nitrate-containing aerosol.

Brown carbon is known to evolve. They also observed a particle type referred to as “tar balls.” While others have seen these, Sedlacek and his colleagues are the first to show that they behave like secondary organic aerosols.

The description of these tar balls isn’t meant to suggest boulder-sized pieces of tar hiding somewhere in the clouds: They are about 250 nanometers in diameter, which makes them about 240 times smaller than the thickness of a human hair.

The group is trying to understand how these tar balls form. These tar balls may help clarify a sampling mystery. The top-down view, from satellites, suggests something different than the bottom-up view, from collecting data from particles. The satellite views indicate there should be more “stuff” in the air.

The bottom-up view may not take these tar balls into account. Not all wildfires produce tar balls, but the data Sedlacek and his collaborators collected suggest that they could represent 20 to 30 percent of the particulate mass in the plume.

In addition to flying above wildfires, Sedlacek also jets to places around the world including Brazil and Ascension Island.

He is also a mentor for two instruments, which means he is responsible for making sure they are functioning. He works with single-particle soot photometers, which measure the amount of black carbon in the air, and the aethalometer, which uses light transmission to determine the concentration of black carbon particles collected on a filter.

With the single-particle soot photometer, Sedlacek looked “at the data in a new way and from that gained insight into the morphology — the shape — of the individual particles, something that nobody had thought to do previously,” Lewis explained in an email. Lewis, who has known Sedlacek for over 10 years and has collaborated on numerous projects, said that Sedlacek is “wonderful to work with” and is a “very careful scientist with keen insight and great attention to detail.”

On Ascension Island, Sedlacek was a mentor in support of another scientist’s field campaign. That effort is exploring how biomass burning aerosols produced in Africa interact with marine clouds as the air mass moves from the west coast of Africa in the general direction of the island.

A photographer and bicyclist, Sedlacek takes numerous pictures of his work.

Sedlacek describes himself as an experimentalist and an observationist. He does not do any of the climate models. His data, however, informs those models and enables other scientists to include more details about the climate and atmosphere.

“Those of us who love to fly get to fly into these plumes,” where they are in an unpressurized cabin, so the outside air makes its way into the plane, he said. They experience considerable turbulence above these fires.

“When we see our instruments and our senses respond at the same time,” he said, “it makes for an unforgettable experience.”