Karl Linden News

Karl Linden: Green Washing, Not Greenwashing: What’s the Best Way to Do Laundry?

Anonymous — Wed, 11 Sep 2024 18:10:43 +0000

Karl Linden: Green Washing, Not Greenwashing: What’s the Best Way to Do Laundry? Anonymous (not verified) Wed, 09/11/2024 - 12:10

The suds that go down the drain can be harmful to wildlife. In this New York Times article, Professor Karl Linden offers tips on how to clean clothes and support nature.

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Karl Linden receives IUVA's Lifetime Achievement Award

Anonymous — Wed, 20 Sep 2023 12:30:38 +0000

Karl Linden receives IUVA's Lifetime Achievement Award Anonymous (not verified) Wed, 09/20/2023 - 06:30

Susan Glairon

Professor Karl Linden was honored with the Lifetime Achievement Award at the International UV Association (IUVA) World Congress, hosted from Sept. 10-13 at the InterContinental Dubai - Festival City hotel in Dubai.

"It was one of the sweetest moments of my career," said Linden, chair of CU Boulder's Department of Civil, Environmental and Architectural Engineering.

During the event, Jennifer Osgood, president of the International Ultraviolet Association (IUVA), called upon those who have worked with Linden, been his student or read his papers to stand.

"Almost the whole room was standing," said Linden, who expressed gratitude to his mentors, colleagues and students. "It was quite overwhelming and humbling. It gave me chills."

The IUVA aims to promote the use of Ultraviolet Technology a leading technology for public health and environmental applications, and to establish itself as the leading authority on the use of Ultraviolet Technology through advocacy within education, industry, research and global public policy sectors.

Professor Karl Linden was honored with the Lifetime Achievement Award at the IUVA World Congress, hosted from Sept. 10-13 at the InterContinental Dubai - Festival City hotel in Dubai. "It was one of the sweetest moments of my career," he said.

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Study shows personal disinfection device safe for use in public spaces

Anonymous — Tue, 18 Apr 2023 23:24:37 +0000

Study shows personal disinfection device safe for use in public spaces Anonymous (not verified) Tue, 04/18/2023 - 17:24

Susan Glairon

Imagine carrying a UV device in your backpack and pulling it out to disinfect your bus seat or restaurant table.

The disinfecting properties of UV light have long been known, along with the dangers of human exposure to it. Now a new Linden Research Group study recently published in the journal Science of the Total Environment confirms the safety of a new portable, handheld disinfecting device using a technology called Far UV-C. The device is safe for use without protective gear on the skin or eyes.

Ben Ma, a postdoctoral researcher in environmental engineering, was the first author on the paper. The study examined the reflectivity of UV rays emitted from the device on various common materials and compared it to the conventional mercury-based UV-C devices.

The study demonstrated that, unlike the conventional UV devices emitting at 254 nm, the new handheld device, which emits Far UV-C rays at 222 nm, does not generate harmful amounts of reflected UV light for the user or nearby people and is safe to be used as a personal surface disinfecting device in hospital or healthcare settings, while traveling or at a restaurant or gym.

We asked Ma to share more on this study, as well as his experiences as a postdoctoral researcher at CU Boulder.

Do you foresee people having their own personal device, and when they go to, let’s say, a movie theater, they disinfect their seat?
That’s basically the idea. We're working with a startup company (Freestyle Partners, LLC) which already has a prototype — a handheld UV device with a battery. Using this device on a surface can kill pathogens like SARS-CoV-2 by 99.9 percent within a couple of seconds. So it's very effective, and it’s very safe.

Can you tell us a little about this paper and its impact?
The paper’s focus is to evaluate and determine the intensity of the reflective radiation from this surface disinfection device. So, if the surface reflects UV radiation, the radiation could bounce back to the person holding it and possibly to people in the surrounding area. The reason we study reflection is because UV radiation can be detrimental to human health, and when you use a UV device for surface disinfection, most likely the exposure is not from the device, but from the reflection.

In this study we tested 21 materials commonly found in public spaces. We studied different materials because different materials have different reflectivity. So, for example, metals tend to have a greater reflectivity than plastics.

Why is this emerging technology safer?
Germicidal radiation has wavelengths between 200 to 280 nanometers. One of the emerging technologies that we are very interested in is the Far UV-C portable handheld device, which emits primarily at 222 nanometers; 222 nanometer UV radiation is much safer for humans compared to 254 nanometers emitted from the conventional mercury-based devices, which are known to be hazardous upon exposure to human skin and eyes.

222 nanometer UV radiation can effectively inactivate all kinds of pathogens but has very poor cellular penetration. It can be blocked by the very top layers of human skin and eyes, whereas 254 nanometer radiation can penetrate through that layer and get to the germinative cells, resulting in adverse health effects. Our study showed that for eye exposure the emerging Far UV-C device is 23 times safer compared to traditional UV and, for skin exposure, 43 times safer.

We also calculated the maximum exposure time, and we found that even considering the worst-case scenario, in most cases the emerging technology is safe to use for surface disinfection for more than eight hours per day.

Scientists say COVID exposure is mostly aerosol and not due to surface contamination. So why is this an important disinfection tool?
I agree that COVID exposure is mainly through aerosol, but surfaces are still a source of SARS-CoV-2 transmission, and COVID as well as other pathogens of concern can be viable on a surface for up to several days. Without disinfection, it will be viable for transmission. Also, there are studies demonstrating that this emerging Far UV-C technology can also be used for aerosol disinfection in occupied public spaces, such as elevators, restaurants and hospitals.

So looking to the future, could the paper have a pretty big impact?
Overall we hope this amazing technology will be used to help reduce the effects of the pandemic and future public health events.

Right now we mainly focus on SARS-CoV-2. But in the real world we encounter pathogens every day, everywhere. So, for example, this device could also be used in kitchens to disinfect pathogens on food, cutting boards and cookwares. If you camp or hike, we actually have a commercialized product using UV to disinfect the water from a creek.

What’s the next step on this research project?
In terms of evaluating reflection and safety of these kinds of sources, our work will support further industry development of UV applications. We are continuing to research these and other UV wavelengths for public health protection in air, water and surfaces.

Our group is working on another study to standardize the testing method to evaluate the surface disinfection performance of UV radiation. Right now we don't have standardized methods to evaluate the effectiveness of a UV disinfection device. The study could provide essential guidance on employing this technology into the real world to help control not just the current pandemic, but maybe future pandemics or any pathogens that we encounter.

Postdoc researcher life at CU Boulder

Where did you grow up?
My hometown is a small town in the northeast part of China. I attended college in Shanghai, then moved to the states. I did my masters at Northwestern in Chicago and then went to the University of Minnesota, where I got my PhD in environmental engineering.

How did you decide on CU Boulder for your postdoc?
There are a lot of considerations when you decide where you want to do a postdoc. The main purpose for doing a postdoc is to get more research experience to prepare to go into academia and to become a professor.

CU Boulder has a really good reputation, especially in environmental engineering, and working with researchers like Dr. (Karl) Linden has been a great opportunity for me. Also, I spent almost seven years in the midwest. After I graduated, I wanted to move to Colorado because I enjoy outdoor activities. I like hiking and probably do one hike per week in the summer. Sometimes I snowshoe.

What's your favorite part of your research?
The part that really excites me is working with Dr. Karl Linden and our research group, which I joined in August 2019. For the past three years our group has focused on using UV technology to help control the COVID-19 pandemic. I have also really enjoyed working with startup companies and other industrial partners, allowing us to not only focus on fundamental research, but also to apply what we study in the lab to the real world.

I also want to mention that CU Boulder has a lot of amazing research programs for college students. I really like working with undergraduate students through research programs like SPUR (Summer Program for Undergraduate Research) and the DLA (�鶹��Ƶy Learning Apprenticeship) program. These research programs help the students better understand what we do in the lab and also gives them a research background. Our recent students, Sam Burke-Bevis and Luke Tiefel, really enjoy working on this project.

Ben Ma, a postdoctoral researcher in environmental engineering, was the first author on a paper that confirmed the safety of a new portable, handheld disinfecting device. The device emits a wavelength of ultraviolet light that is safe for disinfecting public spaces.

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Karl Linden takes reins as CEAE department chair

Anonymous — Thu, 12 Jan 2023 16:53:51 +0000

Karl Linden takes reins as CEAE department chair Anonymous (not verified) Thu, 01/12/2023 - 09:53

Susan Glairon

The Department of Civil, Environmental and Architectural Engineering welcomes Karl Linden as the incoming department chair.

Linden, a CEAE professor and an associate director of the Mortenson Center in Global Engineering, took the reins January 1 from Professor Rich Regueiro, who served as the interim chair since July.

“I am really excited to have this opportunity to work with and help elevate our department as a whole,” Linden said. “We have incredible faculty doing important work for society and the planet, and a top-quality staff that is engaged and supportive.”

Linden spent the fall 2022 semester as a Fulbright Canada Research Chair Scholar at St. Mary’s University in Halifax, Nova Scotia, learning about water quality and treatment practices in Atlantic Canada as well as the challenges facing First Nations communities and small systems due to climate and infrastructure resilience.

Water quality and treatment efforts have been a key focus of Linden’s career. He has made major contributions to the advancement of ultraviolet light systems for disinfection, which are now used by many municipal water systems. He is the author of more than 200 technical papers and was the 2014 Water Reuse Foundation Person of the Year.

Typically Linden teaches undergraduate courses in Water and Wastewater Treatment, Water and Sanitation in Developing Countries and graduate courses in Water Reuse and Advanced Treatment, but will reduce his teaching load due to taking on his new duties as department chair.

Linden has been the Mortenson Professor in Sustainable Development since 2015. He served previously as president of the International UV Association from 2013-15 and then president of the Association of Environmental Engineering and Science Professors from 2018-19. He currently serves on the WHO Water Quality Technical Advisory Group and has received numerous awards including the 2013 Pioneer Award in Disinfection and Public Health from the Water Environment Federation; the 2019 AEESP Walter J Weber Jr. Frontier in Research Award; the 2019 Water Research Foundation Dr. Pankaj Parekh Research Innovation Award; and the 2020 Borchardt-Glysson Water Treatment Innovation Prize. He was the 2020 National Water Research Institute Clarke Prize Laureate.

Linden received MS and PhD degrees in Civil and Environmental Engineering at the University of California Davis.

“In my role as chair I am here to support our faculty, staff and students to enable them to achieve their professional goals – their success is our department’s success,” Linden said. “Equally important is creating a culture where everyone feels valued and part of the CEAE team – faculty, staff and students – and my top goal as chair is to help enable this type of climate. Our continued success will follow from there.”

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Three faculty members headed out on Fulbright Program

Anonymous — Thu, 11 Aug 2022 19:45:41 +0000

Three faculty members headed out on Fulbright Program Anonymous (not verified) Thu, 08/11/2022 - 13:45

The U.S. State Department has offered four Fulbright U.S. Scholar awards to CU Boulder faculty members for 2022–23. The prestigious fellowships, funded through Congress and administered through the Institute of International Education, facilitate teaching and research abroad.

Karl Linden (Canada)

Linden is a professor and the associate director of the Mortenson Center in Global Engineering. Linden’s research in the Canadian province of Nova Scotia will focus on learning about water quality issues faced by rural and Indigenous communities—typically concerns around algal blooms and heavy metals such as mercury and arsenic from industrial mine tailings. These are topics in which collaborators at his host institution, St. Mary’s University, have regional expertise.

Linden hopes to help communities improve their water quality through treatment innovations and to broaden his own perspective through the fellowship, meeting with community partners, local water utilities and shadowing researchers at local universities. The issues he’ll study overlap with water issues in rural areas of Colorado and in Native American communities in the southwest, and this is a chance to bring ideas back to Boulder, he said.

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EPA awards $25,000 to CU Boulder to develop drinking water risk assessment tool

Anonymous — Tue, 28 Jun 2022 20:17:12 +0000

EPA awards $25,000 to CU Boulder to develop drinking water risk assessment tool Anonymous (not verified) Tue, 06/28/2022 - 14:17

The CHRIS project was conceived by CU Boulder alumnus Matthew Bentley (EnvEngr MS'17, PhD'20), who recently completed a postdoctoral fellowship with Professor Karl Linden and is now serving as an American Association for the Advancement of Science fellow at the United States Agency for International Development.

Bentley will serve as an advisor on the project.

Environmental engineering master's student Caleb Larison will be part of the student team, as well as numerous undergraduates who will be hired during the fall 2022 semester.

CU Boulder one of 16 student teams nationwide to be awarded funding to develop innovative solutions to environmental challenges

The U.S. Environmental Protection Agency is awarding $25,000 to a �鶹��Ƶ student team to develop a drinking water risk assessment tool as part of the Agency’s People, Prosperity, and the Planet (P3) Program.

CU Boulder is one of 16 student teams receiving funding for research and innovative solutions to address environmental and public health challenges.

Other projects include a smartphone app to monitor household lead concentrations, a mesh material to prevent shoreline erosion, and a household heating system for Tribal communities that’s cleaner and more efficient.

“The students honored today are leading the way when it comes to developing cutting-edge research to address some of our most challenging environmental concerns,” said Chris Frey, Assistant Administrator for EPA’s Office of Research and Development. “I’m excited to support the next generation of scientists and engineers though EPA’s P3 program.”

With the funding, the CU Boulder team will develop an alpha version of the Chemical Health Risk Identification System (CHRIS) tool to assist in rapid chemical risk assessment and treatment selection for global drinking water sources.

“Chemical pollution is a contributor to global disease burden, and the CHRIS tool will fill an important knowledge gap by providing a wide range of stakeholders with knowledge about possible chemical toxin exposures in drinking water, along with appropriate treatment techniques for mitigation,” said Karl Linden, Mortenson Professor in Sustainable Development in the Department of Civil, Environmental and Architectural Engineering at CU Boulder. “Risk assessment tools such as this represent an important first step toward addressing the impacts of chemical pollutants on global health."

The team, using risk factors such as known chemical occurrence, common chemical sources, and other environmental risk factors, will develop unique risk profiles for drinking water sources under a systematic review process.

The tool will then suggest appropriate technologies and interventions to prevent community exposure to chemical contaminants. This alpha version will be validated against existing occurrence data for specific case studies where risk factors can be identified.

“This funding will help CU Boulder develop an initial version of a critical tool to empower people and communities to know more about the water they drink,” said EPA Regional Administrator KC Becker. “Using the tool, people will be able to make better and more informed choices to protect themselves from chemical pollution.”

EPA’s P3 program is a two-phase research grant program open to teams of college and university students working to design solutions for a sustainable future.

The 16 Phase I recipients announced today will receive grants of up to $25,000 each, which serve as their proof of concept. They will be eligible to compete for a Phase II grant of up to $100,000 to further implement their design in a real-world setting.

CU Boulder one of 16 student teams nationwide to be awarded funding to develop innovative solutions to environmental challenges. The U.S. Environmental Protection Agency is awarding $25,000 to a �鶹��Ƶ student team to develop a...

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CU Boulder researcher earns major award to study water quality challenges in rural Canadian communities

Anonymous — Thu, 09 Jun 2022 20:41:03 +0000

CU Boulder researcher earns major award to study water quality challenges in rural Canadian communities Anonymous (not verified) Thu, 06/09/2022 - 14:41

Jeff Zehnder

Karl Linden has landed a major fellowship to research solutions to water pollution in rural and First Nations communities in Canada.

Linden, the Mortenson Professor in Sustainable Development in the Department of Civil, Environmental and Architectural Engineering at the �鶹��Ƶ, has been selected as a 2022 Fulbright Scholar.

The prestigious U.S. State Department program offers scholars the chance to teach and conduct research around the world to expand American partnerships and share knowledge. Linden will spend the fall 2022 semester at St. Mary’s University in Halifax, Nova Scotia, with a particular focus on water quality issues in Canadian First Nations Communities.

“The solutions engineers typically bring to small communities haven’t been working,” Linden said. “We have these intractable problems of water quality and treatment. We aren’t making the improvements in public health you’d expect to see. Somehow we’re missing something.”

Many First Nations communities in Canada are small and in remote areas, and some do not have safe running water or conventional sanitation.

“I want to help transform how we do engineering by incorporating more diverse solutions,” Linden said. “If we can build on engineering fundamentals but listen to and incorporate indigenous knowledge and values including the centuries of resilience embedded in these communities, we may find a whole new solution set of ideas and designs. It has to start with listening, rather than coming in with pre-conceived answers, which is how we engineers commonly approach problems. I am looking forward to taking the time to meet with communities and understand what kind of problems they want to solve, and then see what it takes to co-create solutions that work in the geographies and with the diverse cultures represented.”

Linden has focused his career on water quality and treatment efforts. He has made major contributions to the advancement of ultraviolet light systems for disinfection, which are now used by many municipal water systems.

“I’ve been working on UV solutions for decades, and it’s really exciting to see your research move into everyday use,” Linden said. “UV technology is now used for everything from single households up to disinfection for New York City, which has the largest water system in the world.”

A particular focus for Linden in Canada will be water quality issues due to algal blooms and heavy metals like mercury and arsenic from industrial mine tailings. These are topics in which his collaborators at St. Mary’s University have regional expertise.

“These metals and algal toxins impact the natural water quality, and the downstream users of these watersheds, including First Nations communities, are bearing the burden of this pollution, which needs to be treated to create safe and potable water,” Linden said.

He hopes to help communities improve their water quality and to broaden his own perspective through the fellowship.

“It’s a short time, just a few months, but I want to meet with community partners, local water utilities, and shadow researchers,” Linden said. “There are a lot of overlaps with water issues we have in rural areas of Colorado and in Native American communities in the southwest, and this is a chance to broaden my perspectives and bring ideas back to Boulder as well.”

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Newest AAAS fellows honored for work on nuclear winter, water treatment, STEM education

Anonymous — Wed, 26 Jan 2022 17:13:59 +0000

Newest AAAS fellows honored for work on nuclear winter, water treatment, STEM education Anonymous (not verified) Wed, 01/26/2022 - 10:13

The American Association for the Advancement of Science (AAAS), the world’s largest general scientific society, today announced that three CU Boulder researchers will join the ranks of its newest class of AAAS Fellows.

CU Boulder faculty named to the prestigious fellows program are: Noah Finkelstein, professor and vice chair of the Department of Physics; Karl Linden, Mortenson Endowed Professor in Sustainable Development; and Brian Toon, professor in the Department of Atmospheric and Oceanic Sciences and research scientist in the Laboratory for Atmospheric and Space Physics (LASP). AAAS honored the researchers for their work studying everything from physics education and nuclear winter to using ultraviolet light to keep water supplies safe for drinking.

Noah Finkelstein. (Credit: Noah Finkelstein)

Brian Toon. (Credit: CU Boulder)

Karl Linden. (Credit: CU Boulder College of Engineering and Applied Science)

The 2021 class of fellows draws from 564 scientists from across the country. Nearly 30 other scientists from CU Boulder have also received this honor since the late 1970s.

“AAAS is proud to bestow the honor of AAAS Fellow to some of today’s brightest minds who are integral to forging our path into the future,” said Sudip Parikh, AAAS chief executive and executive publisher of the Science family of journals, in a statement. “We celebrate these distinguished individuals for their invaluable contributions to the scientific enterprise.”

Terri Fiez, vice chancellor for Research and Innovation at CU Boulder, saluted Finkelstein, Linden and Toon for their new achievements.

“We are thrilled that AAAS is honoring these three pioneering researchers,” Fiez said. “They epitomize CU Boulder’s commitment to research that can improve the lives of people around the world, and to ensuring that this spirit of excellence and innovation translates into education and opportunities for our undergraduates, graduate students and postdocs.”

A lifelong educator

Finkelstein likes to say he has been teaching continuously since he was 12. He first shared his knowledge of Hebrew and computer programming with younger kids through summer camp programs in the early 1980s.

Today, AAAS has recognized Finkelstein’s work in “establishing and advancing the fields of physics education research and institutional transformation in STEM education with an inclusive mindset.”

Finkelstein explores how students learn about physics—and how educators can improve the experiences of budding scientists in their classrooms. He’s studied how college physics classrooms can be more inclusive for women and people of color who are historically underrepresented in the field. In particular, Finkelstein said he wants STEM classrooms to be about more than just memorizing facts.

“If I could snap my fingers and do one thing, it would be to support people in broadening our definition of what education is,” Finkelstein said. “Education is also about socializing individuals so that students coming out of classes think of themselves as science capable and engaged– so that our majors can walk and talk like physicists. They can not only recognize and apply Schrodinger’s Equation but also make sense of it.”

Finkelstein serves as one of the directors of the Physics Education Research group at CU Boulder. He was also a founding co-director of the Center for STEM Learning and sits on the Board of Trustees for the national Higher Learning Commission. He received his doctorate from Princeton University and joined the CU Boulder faculty in 2003.

Clouds overhead

Toon has long had an eye on the skies. AAAS honored the scientist “for fundamental contributions toward understanding the role of clouds and aerosols in the climates of Earth and other planets, and for warning the world of the dangers of nuclear weapons.”

Throughout his career, Toon has examined “virtually every cloud and aerosol system in the solar system and some on exoplanets.”

He’s delved into how the plumes from massive volcanic eruptions and wildfires can influence Earth’s climate and studied the potential dangers of nuclear warfare. Toon and his colleagues previously discovered even a relatively small-scale nuclear conflict could kill tens of millions of people and wreak havoc on food crops across the planet.

“This work influenced the recent United Nations agreement to ban nuclear weapons globally as land mines, biological weapons and poison gases have been banned in the past,” Toon said.

Toon earned his doctorate from Cornell University and has been at CU Boulder since 1997. Among other achievements, Toon received NASA Medals for Exceptional Scientific Achievement in 1983 and 1989 and was one of the lead scientists who contributed to the Intergovernmental Panel on Climate Change’s Nobel Peace Prize in 2007.

Clean water to drink

Linden, professor in the Department of Civil, Environmental and Architectural Engineering, works to help rural communities, municipalities and other entities to control the spread of harmful pathogens such as SARS-CoV-2 in air, on surfaces and in water.

He is acknowledged by AAAS “for distinguished contributions to the field of water treatment engineering, particularly using ultraviolet light for pathogen disinfection and abatement of organic contaminants in water reuse.”

Municipal and industrial water treatment facilities around the world use ultraviolet disinfection to eliminate harmful pathogens like E. coli and Giardia from water supplies in seconds. Linden, however, wants to go smaller—creating nimble and durable technologies that rural communities and countries with limited resources can use to treat their own water supplies.

Linden leads a five-year, $15.3-million project called the Sustainable WASH Systems Learning Partnership through the Mortenson Center in Global Engineering at CU Boulder. In 2020, he won the Borchardt-Glysson Water Treatment Innovation Prize and was named the Clarke Prize Laureate for outstanding achievement in water science and technology.

“I am so honored to become a fellow of AAAS—an organization at the forefront of defending the integrity of science, promoting science-based policy and decision making, strengthening diversity in science and advocating for educational and career opportunities in science and technology,” Linden said.

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Type of ultraviolet light most effective at killing coronavirus is also the safest to use around people

Anonymous — Tue, 26 Oct 2021 17:26:03 +0000

Type of ultraviolet light most effective at killing coronavirus is also the safest to use around people Anonymous (not verified) Tue, 10/26/2021 - 11:26

Scientists have long known that ultraviolet light can kill pathogens on surfaces and in air and water. UV robots are used to disinfect empty hospital rooms, buses and trains; UV bulbs in HVAC systems eliminate pathogens in building air; and UV lamps kill bugs in drinking water.

Perhaps you have seen UV wands, UV LEDs and UV air purifiers advertised as silver bullets to protect against the coronavirus. While decades of research have looked at the ability of UV light to kill many pathogens, there are no set standards for UV disinfection products with regard to the coronavirus. These products may work to kill SARS-CoV-2, the virus that causes COVID-19, but they also may not.

I am an environmental engineer and expert in UV disinfection. In May 2021, my colleagues and I set out to accurately test various UV systems and see which was the most effective at killing off – or inactivating – SARS-CoV-2.

When UV light enters a cell, it breaks the bonds that hold DNA or RNA together. NASA/David Herring via WikimediaCommons

How does UV light kill a virus?

Light is categorized by wavelength – the distance between peaks of a wave of light – and is measured in nanometers. UV wavelengths range from 100 to 400 nanometers – shorter in wavelength than the violet hues in visible light – and are invisible to the human eye. As wavelength shortens, photons of light contain higher amounts of energy.

Different wavelengths of UV light work better than others for inactivating viruses, and this depends on how well the wavelengths are absorbed by the virus’s DNA or RNA. When UV light gets absorbed, the photons of light transfer their energy to and damage the chemical bonds of the genetic material. The virus is then unable to replicate or cause an infection. Researchers have also shown the proteins that viruses use to attach to a host cell and initiate infection – like the spike proteins on a coronavirus – are also vulnerable to UV light.

The dose of light matters too. Light can vary in intensity – bright light is more intense, and there is more energy in it than in dim light. Being exposed to a bright light for a short time can produce the same UV dose as being exposed to a dim light for a longer period. You need to know the right dose that can kill coronavirus particles at each UV wavelength.

Sunburns are caused by UV light damaging skin cells. Ian Hooton/Science Photo Library via Getty Images

Making ultraviolet lights safe for people

Traditional UV systems use wavelengths at or around 254 nanometers. At these wavelengths the light is dangerous to human skin and eyes, even at low doses. Sunlight includes UV light near these wavelengths; anyone who has ever gotten a bad sunburn knows just how dangerous UV light can be.

However, recent research has shown that at certain UV wavelengths – specifically below 230 nanometers – the high-energy photons are absorbed by the top layers of dead skin cells and don’t penetrate into the active skin layers where damage can occur. Similarly, the tear layer around eyes also blocks out these germicidal UV rays.

This means that at wavelengths of UV light below 230 nanometers, people can move around more freely while the air around them is being disinfected in real time.

Researchers used this setup to test multiple different UV lights at various doses to see what it took to kill SARS-CoV-2. Karl Linden, CC BY-ND

Testing different wavelengths

My colleagues and I tested five commonly used UV wavelengths to see which work best to inactivate SARS-CoV-2. Specifically, we tested how large a dose is needed to kill 90% to 99.9% of the viral particles present.

We ran these tests in a biosafety level three facility at the University of Arizona that is built to handle lethal pathogens. There we tested numerous lights across the UV spectrum, including UV LEDs that emit light at 270 and 282 nanometers, traditional UV tube lamps at 254 nanometers and a newer technology called an excited dimer, or excimer, UV source at 222 nanometers.

To test each device we spiked a sample of water with millions of SARS-CoV-2 viruses and coated a petri dish with a thin layer of this mixture. We then shined UV light on the petri dish until we achieved a specific dose. Finally we examined the viral particles to see if they could still infect human cells in culture. If the viruses could infect the cells, the dose was not high enough. If the viruses did not cause an infection, the UV source at that dose had successfully killed the pathogen. We carefully repeated this process for a range of UV doses using the five different UV devices.

While all of the wavelengths we tested can inactivate SARS-CoV-2 at very low doses, the ones that required the lowest dose were the systems that emit UV light at a wavelength of 222 nanometers. In our experiment, it took a dose of less than 2 millijoules of energy per square centimeter to kill 99.9% of viral particles. This translates to needing about 20 seconds to disinfect a space receiving a low intensity of short wavelength UV light, similar to that used in our test.

[Get our best science, health and technology stories. Sign up for The Conversation’s science newsletter.]

These 222-nanometer systems are almost twice as effective as conventional UV tube lamps, which are often used in ultraviolet disinfecting systems. But importantly, the winning lamp also happens to be the safest for humans, too. At the same UV light intensity it takes to kill 99.9% of SARS-CoV-2 in 20 seconds, a person could be safely exposed to 222-nanometer light for up to one hour and 20 minutes.

What this means is that widely available types of UV lamp lights can be used to safely knock down levels of the coronavirus with people present.

Better use of existing tech

Many places or organizations – ranging from the U.S. Air Force to the Space Needle in Seattle to Boeing – are already using or investigating ways to use UV light in the 222 nanometer range to protect public health.

I believe that our findings are important because they quantify the exact doses needed to achieve various levels of SARS-CoV-2 control, whether that be killing 90% or 99.9% of viral particles.

Imagine coffee shops, grocery stores, school classrooms, restaurants and concert venues now made safe by this technology. And this is not a solution for just SARS-CoV-2. These technologies could help protect human health in public spaces in future times of crisis, but also during times of relative normalcy, by reducing exposure to everyday viral and bacterial threats.

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Fox 31 highlights Linden research on UV light disinfection for COVID-19

Anonymous — Mon, 04 Oct 2021 20:12:46 +0000

Fox 31 highlights Linden research on UV light disinfection for COVID-19 Anonymous (not verified) Mon, 10/04/2021 - 14:12

�鶹��Ƶ researchers say a specific wavelength of ultraviolet light is effective at killing the COVID-19 virus and is safe for use in public places like concert halls and airports.

“Of almost every pathogen we have ever studied, this virus is one of the easiest, by far, to kill with UV light,” said senior author Karl Linden, CU Boulder professor of environmental engineering. “It takes a very low dose. This indicates that UV technology could be a really good solution for protecting public spaces.”

UV light use may be a ‘game changer’ for affordable, safe and highly effective systems for reducing viral spread in crowded public places, according to the authors of a study.

COVID-19 is especially susceptible to a specific wavelength – called Far ultraviolet-C, at 222 nanometers – which is safe for human exposure, researchers found.

“There is an opportunity here to save money and energy while protecting public health in the same way. It’s really exciting,” Linden said.

Installing UV lights is cheaper than upgrading entire HVAC systems, according to researchers.

For more information, visit CU’s website.

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Karl Linden News

Karl Linden: Green Washing, Not Greenwashing: What’s the Best Way to Do Laundry?

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Karl Linden receives IUVA's Lifetime Achievement Award

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Study shows personal disinfection device safe for use in public spaces

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Karl Linden takes reins as CEAE department chair

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Three faculty members headed out on Fulbright Program

Karl Linden (Canada)

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EPA awards $25,000 to CU Boulder to develop drinking water risk assessment tool

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CU Boulder researcher earns major award to study water quality challenges in rural Canadian communities

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Newest AAAS fellows honored for work on nuclear winter, water treatment, STEM education

A lifelong educator

Clouds overhead

Clean water to drink

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Type of ultraviolet light most effective at killing coronavirus is also the safest to use around people

How does UV light kill a virus?

Unbiased. Nonpartisan. Factual.

Making ultraviolet lights safe for people

Testing different wavelengths

Better use of existing tech

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Fox 31 highlights Linden research on UV light disinfection for COVID-19

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