Carbon dioxide and carbon monoxide photoproduction quantum yields in the Delaware Estuary

Photochemical mineralization of dissolved organic matter (DOM) plays an important role in the cycling of carbon in estuarine systems. A key to modeling this process is knowledge of apparent quantum yields (AQYs) for the photochemical products. Here we determined spectral AQYs for carbon dioxide (CO2) and carbon monoxide (CO), the main products of DOM photomineralization, along the main axis of the Delaware Estuary. Apparent quantum yields for CO2 photoproduction were determined shipboard using a multi-spectral irradiation system. Carbon monoxide AQYs were determined in stored samples by employing a narrow band spectral irradiation system. A single AQY spectrum described carbon dioxide photochemical production within the estuary whereas CO AQY spectra varied with salinity, suggesting different precursors and mechanisms for the production of these two species. CO2 AQYs were used along with shipboard measurements of DOM absorbance and solar irradiance to calculate photoproduction rates. Calculated CO2 photoproduction rates agreed with directly measured rates (2 to 4 μM CO2 d− 1) within experimental error, supporting the further development and use of AQYs to calculate regional-scale photochemical fluxes.