Air pollution, a warm bedroom and high levels of carbon dioxide and ambient noise all may adversely affect our ability to get a good night’s sleep, suggests a study from researchers with the Perelman School of Medicine at the University of Pennsylvania and the University of Louisville’s Christina Lee Brown Envirome Institute (CLBEI).

The study, published April 18 in Sleep Health, is one of the first to measure multiple environmental variables in the bedroom and analyze their associations with sleep efficiency—the time spent sleeping relative to the time available for sleep. The analysis found that in a group of 62 participants tracked for two weeks with activity monitors and sleep logs, higher bedroom levels of air pollution ( or PM_2.5), carbon dioxide, noise and temperature were all linked independently to lower sleep efficiency.

The study was a collaboration between Penn Medicine and UofL’s CLBEI which is led by Aruni Bhatnagar. The researchers recruited participants from the CLBEI’s National Institutes of Health-funded Green Heart Project that investigates the effects of planting 8,000 mature trees on the cardiovascular health of Louisville residents.

“These findings highlight the importance of the bedroom environment for high-quality sleep,” said study lead author Mathias Basner, professor and director of the division of Sleep and Chronobiology in the department of Psychiatry at Penn Medicine.

The researchers suggest that more research is needed now on interventions that could improve sleep efficiency by reducing exposures to these sleep-disrupting factors.

“This could be as simple as leaving a bedroom door open to lower carbon dioxide levels, and using triple-pane windows to reduce noise,” Bhatnagar said. “We also applied for (future) funding that will allow us to investigate whether planting trees can improve sleep and cardiovascular health through improving health behaviors and the bedroom environment.”

About the study

In addition to work and family obligations that , a quickly changing environment due to growing urbanization and climate change seems to have made it harder to get a good night’s sleep. Sleep that is of inadequate duration, or inadequate efficiency due to frequent disruption (“tossing and turning”), affects work productivity and quality of life. It also has been linked to a higher risk of chronic diseases including heart disease, type 2 diabetes, depression and dementia.

This research is among a limited number of studies that looked at associations between multiple objectively measured factors in the sleep environment—such as noise and temperature—and objectively measured sleep.

For each of the environmental variables measured, the researchers compared sleep efficiency during exposures to the highest 20 percent of levels versus lowest 20 percent of levels. Through this analysis, they found that high noise was associated with a 4.7 percent decline in sleep efficiency compared to low noise, high carbon dioxide with a 4.0 percent decline compared to low levels, high temperature with a 3.4 percent decline compared to low temperature, and high PM_2.5 with a 3.2 percent decline compared to low PM_2.5. Two other sleep environment variables, relative humidity and barometric pressure, appeared to have no significant association with sleep efficiency among the participants.

Interestingly, only bedroom humidity was associated with sleep outcomes assessed with questionnaires, such that higher humidity was associated with lower self-reported sleep quality and more daytime sleepiness. This suggests that studies based on questionnaires may miss important associations readily detected by objective measures of sleep. This is not surprising as humans are unconscious and unaware of themselves and their surroundings during large portions of their sleep period.

Also, most study participants rated humidity, temperature and noise levels in the bedroom as “just right” regardless of the actual exposure levels.

“We seem to habituate subjectively to our bedroom environment, and feel there is no need to improve it, when in fact our sleep may be disturbed night after night as evidenced by the objective measures of sleep we used in our study,” said Basner.

Earth depends on balanced levels of greenhouse gases for our warm climate, averaging 59^oF, to sustain plant and animal life. Since the Industrial Revolution, burning of fossil fuels for energy has resulted in the excessive accumulation of atmospheric gases such as CO₂, raising the temperature of the planet.

Greenhouse gas levels are the highest ever recorded and continue to rise as worldwide energy use is projected to double in the next 10 years. Flue gas is the smoky exhaust from a furnace, boiler or generator and, on a larger scale, the gas that results from combustion at power plants. A major portion of U.S. greenhouse gas emissions (approximately 33%) are attributable to the flue gas resulting from electricity generation by utilities.

While most research into electrochemical reduction of carbon dioxide has relied on pure gas feedstocks, CO₂ is more dilute in flue gas at typically less than 20%. The Conn Center project will pursue the development of a stable and efficient method to convert the CO₂ directly from a power plant exhaust stream, which would aid in making the overall process more cost-effective.

Flue gas contaminants can degrade the performance of an electrolysis reactor, making the direct electrochemical conversion of flue gas CO₂ a challenging prospect. The UofL team is working on novel molecular catalysts to guide the selectivity of the reaction within a new high-performance reactor designed for use with both water and organic solvent.

The major challenge of utilizing flue gas CO₂ to produce carbon-based chemicals is to create technology that is efficient, economical and achievable at a commercial scale. Meeting these three criteria would provide an economic incentive for industry by adding value to their waste instead of emitting it to the atmosphere.

These power plant emissions will be processed to convert CO₂ to useful products, including those where the single carbon atoms in CO₂ are combined to form larger compounds with two to four carbon atoms. Such products include formic acid, ethanol and methyl formate, all of which are currently produced using fossil fuels.

The research team is led by Joshua Spurgeon, Ph.D., theme leader for Solar Fuels at the Conn Center for Renewable Energy Research in the , and UofL chemistry professor Craig Grapperhaus, Ph.D., in conjunction with the University of North Dakota’s Institute for Energy Studies. This research has been funded by the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL). Funding of $1.25 million over two years was secured by Spurgeon and Grapperhaus to conduct the research, which has enabled the recruitment of several graduate students and postdoctoral scholars and will include research opportunities for undergraduate students.

The partnership also includes an alumnus of the University of Louisville Speed School. Nolan Theaker, one of Spurgeon’s previous undergraduate researchers, is now a Ph.D. student at the University of North Dakota and a research engineer with the Institute for Energy Studies. Theaker will lead the effort at UND to develop methods to process the flue gas for stable and efficient operation in the electrolyzer. This partnership includes Minnkota Power Cooperative, which will provide access to its coal-based post-combustion flue gas and analysis capabilities.

Spurgeon and Grapperhaus designed this project based on their from similar research on electrochemical conversion of CO₂, including Spurgeon’s work on electrochemical CO₂ reactors and Grapperhaus’s work on molecular catalysts, which bind CO₂ and assist the conversion. In the new effort, they will pursue a high-performance reactor design capable of meeting the metrics necessary for a commercially viable process. This includes achieving much higher operating current densities, similar to water-based electrolyzers, than typical laboratory measurements and very high selectivity (~90%) for the desired chemical products.

“Electrochemical reduction of CO₂ allows for renewable energy-driven production of chemicals and fuels in a distributed and modular fashion,” said Mahendra Sunkara, director at Conn Center. “Conn Center is looking towards the development of a CO₂ electrolyzer in the next five years.”