Development of a High-throughput, Temperature-controlled LED-based Instrument to Characterize the Wavelength Dependence of Photochemical Reactions in Aquatic Ecosystems

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Aquatic photochemistry is an interdisciplinary field that examines how sunlight-driven reactions impact the fate and composition of diverse materials in surface waters, including major and minor elements, inorganic and organic pollutants, and biomolecules. Arguably the largest knowledge gap in the aquatic photochemistry discipline is the wavelength dependence of sunlight-driven reactions. That is, while the suite of possible reactions is reasonably well understood, knowledge of how the reaction efficiencies and rates vary by wavelength is limited, largely owing to key shortcomings of current instrumentation. This project aims to overcome these shortcomings by designing, developing, and validating a light-emitting diode (LED) based instrument that improves sample throughput, offers a wider range of sunlight wavelengths to probe, is temperature-controlled, and is field portable. The researchers expect that this new instrument will permit rapid growth in knowledge about the wavelength dependence of a wide variety of photochemical reactions in natural and engineered systems, and, consequently, improve estimates of photochemical reaction rates across space and time. The researchers will serve as a mentor in the Community College Research Experiences at Woods Hole Oceanographic Institution, a program focused on promoting ocean science, technology, and engineering skills and capacity building among community college students, an underappreciated and underutilized resource of talented and diverse undergraduates. Accurate assessment of photochemical reaction kinetics in surface waters requires knowledge about the light available at different wavelengths throughout the water column and the photochemical reaction efficiency, or apparent quantum yield (AQY; mol product mol-1 light absorbed) at those wavelengths. However, current approaches to characterize AQY spectra have many disadvantages, including costs, sample throughput, ease of use, and portability. The researchers have developed and validated a prototype reactor assembly to directly probe AQY spectra of aquatic photochemical reactions. The prototype uses ultraviolet (UV) and visible LEDs to generate high power, narrow banded, and spatially uniform irradiance. In this project, the researchers will scale-up and improve upon the prototype by designing, developing, and validating a new instrument that is electronically-controlled, has upward of a four-fold greater sample capacity, has at least ten-fold higher optical power, has an extended wavelength range from the UV-C to the visible light region, is temperature-controlled, and is field portable. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.