Regional difference in the microheterogeneous distribution of singlet oxygen photoproduction from soil-derived...

Soil-derived dissolved organic matter (SDOM) is a critical terrestrial input that governs the photochemical reactivity of aquatic ecosystems. Its molecular composition exhibits significant variations along a latitudinal gradient, which in turn affects the microheterogeneous distribution and efficiency of photochemically produced reactive intermediates. This study deciphers spatial disparities and molecular mechanisms underlying the microheterogeneous photoproduction of singlet oxygen (¹O₂) by SDOM across different regions. The results demonstrated that the microheterogeneous distribution of ¹O₂ was more pronounced in high-latitude SDOM and gradually weakened toward lower latitudes. This spatial disparity was primarily governed by the SDOM's aromaticity and the abundance of nitrogen-containing functional groups, which correlated positively with ¹O₂ heterogeneity, while correlated negatively with its sulfur-containing functional groups. Further analysis revealed that the aromaticity and nitrogen content of SDOM decreased from high to low latitudes. Conversely, sulfur content displayed a distinct increasing trend. Furthermore, the microheterogeneous distribution of ¹O₂ generation in high-latitude SDOM was predominantly governed by high molecular weight fractions (<100 kDa), while in low-latitude SDOM, low molecular weight fractions (<10 kDa) served as the primary contributors. These findings provide a theoretical support for in-depth research on the latitude-dependent photochemical activity of SDOM within the study area, with significant implications for spatial variations in the degradation of aquatic pollutants.