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

The steady-state concentration of singlet oxygen within a lake ([(1)O(2)](SS)) is an important parameter that can affect the environmental half-life of pollutants and environmental fate modelling. However, values of [(1)O(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 [(1)O(2)](SS) within lake epilimnia were identified. It was found that the depth of the epilimnion has the largest impact on depth-averaged [(1)O(2)](SS), with a factor of 8.8 decrease in [(1)O(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 [(1)O(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 [(1)O(2)](SS) within an average epilimnion depth of 9.0 m was found to be 5.8 × 10(−16) M and the near-surface value of [(1)O(2)](SS) was found to be 1.9 × 10(−14) M. We recommend a range of 6 × 10(−17) to 5 × 10(−15) M as being more representative of [(1)O(2)](SS) values within the epilimnia of lakes globally and potentially more useful for estimating pollutant lifetimes than those calculated using [(1)O(2)](SS) values that correspond to near-surface, summer midday values. This work advances our understanding of [(1)O(2)](SS) inter-lake variability in the environment, and provides estimates of [(1)O(2)](SS) for practitioners and researchers to assess environmental half-lives of pollutants due to reaction with singlet oxygen.