Copper Binding with Snow-Derived Dissolved Organic Matter: Insights from Excitation–Emission Matrix Spectroscopy and Two-Dimensional Correlation Spectroscopy

The binding interactions between heavy metals and dissolved organic matter (DOM) derived from snow remain largely unexplored. In this study, DOM was extracted from snow samples, and its composition was characterized using excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). The fluorescent properties of DOM were characterized, and the binding behavior of DOM with Cu(II) ions was further investigated through EEM-PARAFAC, a modified Stern–Volmer complexation model, and two-dimensional correlation spectroscopy (2DCOS). Fluorescence analysis revealed that the composition of WDOM was significantly influenced by both terrestrial sources and microbial activity. The EEM-PARAFAC revealed that snow-derived DOM consisted primarily of a tyrosine-like component (75%) and a humic-like component (25%). The modified Stern–Volmer model results revealed that the humic-like component exhibited a greater number of binding sites and stronger binding affinity (f = 0.8963, log KM = −3.636) compared with the tyrosine-like component (f = 0.4963, log KM = −3.912), suggesting that the humic-like component was the dominant contributor to Cu(II) binding. The 2DCOS analysis further showed that the humic-like component exhibited preferential binding to Cu(II) ions over the tyrosine-like component. These findings provide new insights into the binding process between Cu(II) and snow-derived DOM, enhancing our understanding of heavy metal behavior in wet atmospheric deposition.