Louisville residents are well acquainted with the challenges caused by urban heat, such as higher utility bills and serious health problems that disproportionately affect residents with pre-existing health conditions.

The new study also involves Brian Stone, a professor and director of the Urban Climate Lab at Georgia Institute of Technology, whose previous work identified Louisville as having one of the fastest-growing urban heat islands in the nation.

An urban heat island exists when the built environment – buildings, sidewalks and paved roads – absorbs more heat than natural surfaces such as grass, trees and exposed soil, causing higher air temperatures. Those heat-absorbent surfaces also retain that heat during nighttime hours.

“Louisville has been at the forefront of studying urban heat for years, thanks to foundational work like ,” Stone said. “However, the climate continues to change and the city continues to grow. This new project provides an unprecedented, highly detailed look at current temperatures and the specific cooling power of different types of vegetation in 2025. It’s about giving Louisville the most up-to-date, actionable science to make truly impactful decisions, which is especially relevant as residents are facing extreme heat right now.”

The project will use advanced climate models to generate highly detailed, hourly temperature maps for June, July and August 2025. These maps will cover the entire Jefferson County area – nearly 398 square miles – at a remarkable resolution of 100 meters, offering an unparalleled view of where heat is most intense across Louisville’s urban core. Sensors installed by the Envirome Institute around Louisville will provide data to help enrich the model. The project, supported by the James Graham Brown Foundation, begins in July and is expected to be completed within three months.

Beyond traditional temperature readings, the study will also measure factors that provide a more complete picture of actual heat stress experienced by individuals.

A key focus of this research involves an in-depth analysis of how various tree canopies reduce temperatures. Researchers will investigate which areas benefit most from new tree plantings and how different tree species — and whether they are coniferous or deciduous — impact cooling differently.

Precise insights gained from the new project also will enhance and expedite the Envirome Institute’s research into health benefits of additional greenness, including the and the in downtown Louisville.

“At the Envirome Institute, our mission is to understand how the environment shapes our health. This new analysis comes at a time when we are all facing tremendous heat burden,” said Aruni Bhatnagar, executive director of the . “By precisely mapping urban temperatures and land cover like trees and other vegetation, we’re not just gathering data; we’re creating a powerful new tool. This research will allow us to strategically use urban greening as a direct intervention to improve public health in our downtown core and across every neighborhood in Louisville.”

The project will also analyze heat-related mortality at the neighborhood level in order to highlight areas where residents are most vulnerable to heat-related illnesses and where targeted interventions are most urgently needed to improve public health outcomes. This insight will help guide tree planting initiatives by and other partners, ensuring that efforts maximize cooling benefits.

“TreesLouisville has been working tirelessly to expand our urban canopy, utilizing data from previous assessments to guide our strategic planting,” said Cindi Sullivan, executive director of TreesLouisville. “This new study will provide us with an even sharper focus, pinpointing exactly where our efforts will have the greatest impact and helping us choose the right trees for the right places to achieve significant temperature reductions for our community. This is particularly urgent as we continue to push towards our city’s goal of every neighborhood having at least 30% canopy cover.”

Article is co-authored by Ted Smith.

• $2.4 million from the National Institute on Aging will support work by Bradford Hill to investigate how aging leads to reduced blood flow to the heart in older individuals. Hill will study these changes and how this dysfunction could be prevented or corrected. The work may lead to opportunities to prevent age-dependent decline in exercise capacity and promote healthy aging.
• $3.4 million from the National Heart Blood and Lung Institute was awarded for a clinical trial to test whether treatment with the nutritional supplement carnosine improves symptoms and progression in peripheral artery disease in which narrowing of arteries reduces blood flow to arms or legs. Aruni Bhatnagar, Shahid Baba and Amit Dwivedi will conduct the trial.
• $4.67 million from the National Institute of Environmental Health Sciences will support the Green Heart Louisville Project, which studies how an increase in the number of trees and shrubs affects heart health. The team, led by Bhatnagar, recently reported results from their work that began in 2018 in South Louisville. The new award will allow the team to continue to gather data on community health for the next five years as the planted trees continue to grow.
• $ 0.8 million from the Department of Defense was awarded to Daniel Conklin for a two-year project to investigate the role of inhaled agents in Gulf War Illness (GWI), a chronic condition affecting 25-32% of Gulf War veterans. GWI involves chronic pain, muscle fatigue, cognitive impairment, migraines and stroke. Conklin will investigate whether inhalation of volatile organic compounds and particulate matter from burning oil wells, burn pits, contaminated sand and chemical and biological weapons may have led to repeated local and systemic inflammation, causing the condition.

This most recent funding adds to the $11.6 in grants awarded to institute researchers announced earlier this year.

The research, led by Aruni Bhatnagar, professor of medicine and director of the UofL Christina Lee Brown Envirome Institute, was published ahead of print in the .

Previous studies have shown that proximity to green space — trees and other vegetation — can lower blood pressure levels and the risk of heart disease. A number of environmental factors may come into play, including increased opportunity for outdoor exercise, reduced mental stress and socioeconomic status. However, the relationship between vascular (blood vessel) health, green space and air pollution has not been fully explored.

In this , researchers looked at the arterial stiffness of adult volunteers with co-occurring conditions such as obesity, high blood pressure, diabetes and high cholesterol, that put the volunteers in the moderate-to-severe risk category for heart disease.

“Although we have known for a long time that exposure to air pollution has adverse effects on our blood vessels, this study shows that those who live in greener neighborhoods may be less affected,” Bhatnagar said. “Therefore, one way of preventing the harmful health effects of air pollution may be to make neighborhoods more green.”

Using study participants’ residential addresses and data from the U.S. Geological Survey and local Environmental Protection Agency monitoring stations, the research team analyzed environmental factors where the volunteers lived, including:

• Vegetation index, including the amount of and variation in greenness levels within 200-meter and one-kilometer (0.62 miles) radii around each volunteer’s home.
• Particulate matter, tiny toxic particles invisible to the naked eye, in the air.
• Levels of ozone, a colorless, toxic gas and significant air pollutant.

At times when the particulate matter and ozone levels were high, participants had higher levels of arterial stiffness, however, those who lived in areas with more flora had better blood vessel function. Trees and other greenery offset vascular dysfunction that air pollution causes, the researchers explained.

In previous work, the researchers found that individuals who live in areas with a large amount of greenness show lower exposure to volatile chemicals and have greater household income. In the current study, they explored the relationships between greenery, air pollution and arterial stiffness and found a similar correlation between the U.S. Geological Survey’s normalized difference vegetation index and average household income. Even when adjusting for self-reported lifestyle habits such as exercise and smoking — 70% of the volunteers were nonsmokers — the researchers found that “the effects of green spaces on hemodynamic function are largely independent of median household income, physical activity levels and tobacco use.”

“These findings indicate that living in green areas may be conducive for vascular health and that the [favorable] effects of greenness may be attributable, in part, to attenuated exposure to air pollutants such as [particulate matter] and ozone,” said Daniel Riggs, UofL biostatistician and the study’s first author.

This research was conducted in conjunction with the Green Heart Project, a first-of-its-kind study of the effects of plants on human health, led by researchers at the .

As part of community testing for Phase II of the , MSD is providing samples from eight sites in its vast network of pipes and five treatment facilities which are sent weekly to UofL and research collaborators at Arizona State University for virus analysis.

The laboratory at ASU will use RT-PCR tests, a technique for detecting genetic material of the virus, to count copies of SARS-CoV-2 virus RNA in the wastewater and sewage sludge samples. The researchers believe the presence of this RNA sequence is an indicator of the level of infection with the virus in a given community.

To support this work and other aspects of the Co-Immunity Project, a groundbreaking collaboration to track and curb COVID-19, UofL has received a new $1 million gift from the Owsley Brown II Family Foundation.

“Traditionally, science has had difficulty addressing the interdependent nature of people and their environment or factoring in the many forms of human health, including environmental health and the water we all depend on. The Envirome Institute was founded to fill that void,” Christina Lee Brown said. “The challenges of this pandemic have made the need to learn how to make decisions through all forms of health all too clear, and I’m so proud the team here is at the national forefront of the response. The Co-Immunity Project, especially now with this singular partnership with MSD, puts Louisville and Kentucky at the cutting edge nationally in terms of virus monitoring.”

This research is part of the Co-Immunity Project’s Phase II, last week, which also includes testing 2,400 individuals for SARS-CoV-2 infection and antibodies. By concurrently testing individuals and wastewater from different parts of Jefferson County, the researchers hope to develop a “virus radar” to track the spread of the virus in the county. The “virus radar” could be used to identify hot spots of viral infections and even as an early warning sign of future outbreaks in an area. This information could be used to guide public health actions and social restrictions to reduce future surges.

“MSD has a team of skilled professionals who are already taking samples as part of our operations and regulatory requirements. It was a natural extension to offer help to the researchers at the University of Louisville for this important COVID-19 research,” said MSD Executive Director Tony Parrott.

MSD wastewater operators and lab staff already have personal protective equipment and follow best practice guidelines from the Occupational Safety and Health Administration and the Centers for Disease Control and Prevention in their daily work. These measures also protect the safety of MSD employees who obtain the samples for this research.

The reports that to date, there have been no cases in the U.S. or elsewhere in the developed world of infection of a wastewater employee with the COVID-19 virus as a result of treatment operations. 

UofL has offered additional MSD employee testing as part of this research collaboration. MSD employee time for supporting this project is funded by the Co-Immunity Project. The project is part of Metro Louisville’s COVID-19 testing framework that includes extensive testing and contact tracing to contain COVID-19 in the city.

“This collaboration builds off years of research partnership with MSD and our collaborators at Arizona State University,” said Ted Smith, director of the Center for Healthy Air, Water and Soil in the UofL Christina Lee Brown Envirome Institute. “We hope to learn quickly how coronavirus detection in our wastewater can be a useful input to Louisville’s overall COVID-19 test and containment effort.”

This type of testing has been demonstrated to be a reliable indicator of infection in entire communities. Recently, Yale University published showing that the amount of virus in daily samples taken between March 19 and May 1 was a seven-day leading indicator of positive clinical tests for COVID-19 in the New Haven, Connecticut, population of 200,000.

“We are incredibly grateful to the Owsley Brown II Family Foundation for funding the important work of the Co-Immunity Project,” said Aruni Bhatnagar, director of the UofL Envirome Institute. “This research, combined with the other components of the project, may provide new ways of understanding this emerging area of epidemiology and guide Louisville and other communities in responding effectively to COVID-19, and perhaps other infectious diseases as well.”

The Co-Immunity Project is a collaboration of the UofL Christina Lee Brown Envirome Institute, the Louisville Healthcare CEO Council and three health systems in Louisville – Baptist Health, Norton Healthcare and UofL Health.