Influences of molecular composition in dissolved organic matter on its reactivity with chlorine radicals (Cl• and Cl2•−)

Dissolved organic matter (DOM) is a major scavenger of chlorine radicals (e.g., Cl• and Cl2•−) in water. However, there is limited literature addressing the impact of DOM molecular composition on its reactivity towards chlorine radicals. This work focused on discovering the relationships between DOM molecular composition and its reactivity towards Cl• and Cl2•−. The molecular composition of 23 DOM isolates from different sources was characterized using high-resolution mass spectrometry, and their rate constants with Cl• (kDOM-Cl•) and Cl2•− (kDOM-Cl2•−) were determined using laser flash photolysis and competition kinetics. Orthogonal partial least squares (OPLS) analysis model was then used to identify the most correlated and effective predictors of kDOM-Cl• and kDOM-Cl2•−. The kDOM-Cl• positively correlated to higher unsaturation and aromaticity while negatively correlated to the proportion of several N- and S-containing formulas. The kDOM-Cl2•− values showed positive correlation with unsaturation and aromaticity while showing negative correlation with the proportion of CHOPwa formulas. These observations suggest that while unsaturation and aromaticity serve as useful indicators of reactivity with chlorine radicals, non-oxygen heteroatom-containing formulas within the DOM isolates play a pivotal role in governing their interactions with chlorine radicals.