Factors affecting the mixed-layer concentrations of singlet oxygen in sunlit lakes

The steady-state concentration of singlet oxygen within a lake ([O-1(2)](SS)) is an important parameter that can affect the environmental half-life of pollutants and environmental fate modelling. However, values of [O-1(2)](SS) are often determined for the near-surface of a lake, and these values typically do not represent the average over the epilimnia of lakes. In this work, the environmental and physical factors that have the largest impact on [O-1(2)](SS) within lake epilimnia were identified. It was found that the depth of the epilimnion has the largest impact on depth-averaged [O-1(2)](SS), with a factor of 8.8 decrease in [O-1(2)](SS) when epilimnion depth increases from 2 m to 20 m. The next most important factors are the wavelength-dependent singlet oxygen quantum yield relationship and the latitude of the lake, causing variations in [O-1(2)](SS) by factors of 3.2 and 2.5 respectively, over ranges of representative values. For a set of representative parameters, the depth-averaged value of [O-1(2)](SS) within an average epilimnion depth of 9.0 m was found to be 5.8 x 10(-16) M and the near-surface value of [O-1(2)](SS) was found to be 1.9 x 10(-14) M. We recommend a range of 6 x 10(-17) to 5 x 10(-15) M as being more representative of [O-1(2)](SS) values within the epilimnia of lakes globally and potentially more useful for estimating pollutant lifetimes than those calculated using [O-1(2)](SS) values that correspond to near-surface, summer midday values. This work advances our understanding of [O-1(2)](SS) inter-lake variability in the environment, and provides estimates of [O-1(2)](SS) for practitioners and researchers to assess environmental half-lives of pollutants due to reaction with singlet oxygen.

Automated summary

This study identified the environmental and physical factors that have the largest impact on the steady-state concentration of singlet oxygen within lake epilimnia, including epilimnion depth, singlet oxygen quantum yield relationship, and latitude of the lake. Recommendations were made to use more representative values for estimating the singlet oxygen concentration within the epilimnia of lakes globally, which may be more useful for assessing the environmental half-lives of pollutants.