Separation was insufficient for PEGs with MWs below ~2000 Da (filled green peak area below 20 mins of elution in Figure ) and above ~6400 Da (filled purple peak starting above 810 mins of elution in Figure ). Fitting the Monte Carlo simulation with increments of 0.1 𝑆𝑖𝐶 (parameters see above, dashed lines) to the measured cumulative MW distribution data (solid lines) resulted in estimated 𝑆𝚤𝐶 """"" of 1.2, 2.1 and 3.9 for t1, t2, and t3, respectively (Figure ). The good agreement between the fits and the experimental data suggests that the reaction-limited and diffusion-limited regimes in the cutting kinetics of the PEG chains by •OH assumed in the simulations are in good agreement with the experimental observations. The slightly higher fitted (dashed line) than experimental (solid line) abundances of PEG scission products with MW > 4500 Da may reflect that the concentrations of PEGs in this MW range were low, particularly at t3, and may have approached the limit of quantification of the HPLC-CAD method. The fitting also revealed that the experimental design resulted in realistic environmental scenarios (i.e., 𝑆𝚤𝐶 """"" from 1 to 4), in good agreement with 𝑆𝚤𝐶 """"" values anticipated for environmentally realistic steady state •OH concentrations ([•OH]SS = 10 -16 M) and residence times between 12 hours and 3 days (Figure ).