Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Upper Newport Back Bay near-shore surface waters at inlet, mid-estuary and outlet. Site 1 (33.650327, -117.8671967), located at the San Diego creek inlet; site 2 (33.6302266, -117.8859726), located mid-estuary; and site 3 (33.6181867, -117.9051099), located near the Newport Beach marina and Pacific Ocean outlet. 

Surface water (<5 cm) was sampled in the morning from the shore, stored in amber glass bottles, transported to the laboratory, filtered through 0.2 micron Durapore filters and stored in the fridge.  

Fluorescence lifetimes were measured using a Horiba DeltaFlex Lifetime System. The DeltaFlex system is a modular Time Correlated Single Photon Counting (TCSPC) system consisting of a high repetition rate LED source, a DD-C picosecond diode controller, a PPD picosecond photodetection module with DDS-1 power supply, and a DH-HT high throughput TCSPC controller.  The timing electronics has almost no counting photon loss and 10 ns dead times (Horiba Inc). Measurements were made with three different pulsed LED sources (DeltaDiode DD-260, DD-280, DD-340) with peak wavelengths of 268 nm, 285 nm and 338 nm and average power of 5 µW, 10 µW, and 2 µW, respectively. The bandwidth and maximum repetition rate for all LED sources was ~ ± 10 nm and 20 MHz respectively.  An instrument response function (IRF) was measured using a LUDOX AS-40 inorganic scattering suspension (Sigma Aldrich) solution.  

This is a summary of methods from De Bruyn et al., 2025 (see related publications).

There are a number of methods used to obtain lifetime information from time-resolved fluorescence data. The most common approach, and the approach used here, is the discrete component approach (DCA; Kumke et al., 1998a and b). DCA involves fitting the observed decay to an exponential function of the form:

F(t) = A + B1 e-(t/ τ1) + B2 e-(t/ τ2) + B3 e-(t/ τ3) +….                                                           (1)

 Here A is an offset, Bi are the component amplitudes which reflect the initial fluorescence intensity or population of each component, and τi are the lifetimes of each component.  Amplitudes are reported directly as Bi or as relative values i.e. %Bi = Bi/(B1 +B2 +B3…) x 100.  The fractional contributions of each component to total fluorescence (the fraction of fluorescence photons received from a specific decay component) are given by (Kumke et al., 1998a and b; Chen et al., 2020):

f i = Bi τi / (B1 τ1 + B2 τ2 + B3 τ3)                                                                    (2)

The fractional contribution (fi) is directly proportional to the steady-state fluorescence intensity of a given component.

This is a summary of methods from De Bruyn et al., 2025 (see related publications).

* reorganized daata table to long format
* added sampling site latitude and longitude to data table

NSF Award Abstract

Ethanol is added to gasoline to increase octane levels and lower the concentrations of carbon monoxide and surface ozone in the atmosphere. As a renewable fuel, ethanol may also help decrease our dependence on gasoline. Increased use of ethanol in the United States and globally as a fossil fuel substitute and additive is expected to increase ethanol levels in the atmosphere. Atmospheric ethanol is converted to acetaldehyde which is a hazardous pollutant. To understand the impact of increasing ethanol usage, it is important to understand the cycling of ethanol and acetaldehyde in the environment--how they are produced, consumed, and interconverted. Because these compounds can cross from air into water, this requires understanding what happens to these compounds in both the atmosphere and in seawater and other surface waters. This proposal focuses on improving our understanding of processes that produce and consume ethanol and acetaldehyde in coastal seawater and other coastal surface waters like estuaries and salt marshes. This project will measure the rates of photochemical production of ethanol and acetaldehyde, as well as their chemical and biological degradation rates. The project will also measure the rate and efficiency of the biological production of acetaldehyde from ethanol by microbial organisms in these waters. The scientists have an excellent track record of involving undergraduate students, including underrepresented minorities, in their research and as co-authors on publications, a trend they plan to continue with this project. These students would be trained in analytical chemistry and environmental research and would present their research findings at local and national conferences. Lastly, the PIs also plan outreach activities with high school STEM programs to improve student diversity in environmental research.

The primary sink for ethanol in the troposphere is reaction with OH to produce acetaldehyde. Acetaldehyde levels in the troposphere are also expected to increase with increased use of ethanol. Changes in the atmospheric concentrations of these species are expected to have a significant impact on the oxidative capacity of the troposphere. To understand future impacts, it is important to understand current tropospheric budgets which have significant uncertainties for both species. One of the largest sources of uncertainty is the role of the oceans and surface waters in cycling these species into and out of the troposphere. The current understanding is limited by the very small database of ambient concentration measurements in both air and water and an incomplete insight into the processes that control concentrations in seawater and surface waters; these processes represent a complex interplay between biological and photochemical sources and sinks, and air-water exchange. To improve the current understanding of the cycling of ethanol and acetaldehyde in coastal seawater and surface waters, this project will measure: 1) chemical and biological degradation rates of ethanol and acetaldehyde in coastal waters; 2) the rate and efficiency of the biological production of acetaldehyde from ethanol by microbial organisms; 3) ethanol and acetaldehyde concentrations in air and surface waters; 4) the ethanol and acetaldehyde source strength of estuary and saltmarsh sediments; and 5) ethanol and acetaldehyde photochemical production rates in surface waters.

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.