Prediction of Photochemically Produced Reactive Intermediates in Surface Waters via Satellite Remote Sensing

Absorption of solar radiation by colored dissolved organic matter (CDOM) in surface waters results in the formation of photochemically produced reactive intermediates (PPRIs) that react with pollutants in water. Knowing the steady-state concentrations of PPRIs ([PPRI]_ss) is critical to predicting the persistence of pollutants in sunlit surface waters. CDOM levels (a₄₄₀) can be measured remotely for lakes over large areas using satellite imagery. Laboratory measurements of [PPRI]_ss and apparent quantum yields (Φ) of three PPRIs (³DOM*, ¹O₂, and ^•OH) were made for 24 lake samples under simulated sunlight. The total rate of light absorption by the water samples (R_a), the rates of formation (R_f), and [PPRI]_ss of ³DOM* and ¹O₂ linearly increased with increasing a₄₄₀. The production rate of ^•OH was linearly correlated with a₄₄₀, but the steady-state concentration was best fit by a logarithmic function. The relationship between measured a₄₄₀ and Landsat 8 reflectance was used to map a₄₄₀ for more than 10 000 lakes across Minnesota. Relationships of a₄₄₀ with R_f, [PPRIs]_ss, and R_a were coupled with satellite-based a₄₄₀ assessments to map reactive species production rates and concentrations as well as contaminant transformation rates. This study demonstrates the potential for using satellite imagery for estimating contaminant loss via indirect photolysis in lakes.