AbstractThe peroxymonocarbonate mono-anion (HCO4─) is generated in solutions containing bicarbonate anions (HCO3─) and hydrogen peroxide (H2O2). The mono-anion is believed to have a pKa value of ca. 10 and as such would start dissociating to the di-anion (CO42─) at pH ca. 8. The mono-anion should demonstrate electrophilic properties, while the di-anion should be a nucleophile. Results that appear to be due to electrophilic reactions of HCO4─ were presented in Part 1 of this series for lignin model compounds (LMCs) and chemical pulps. Some evidence was also observed for nucleophilic reactions with LMCs in the pH range of 8.8 to 9.5. Results are now being presented for mechanical pulp brightening, where nucleophilic reactions were observed. Hydrogen peroxide decomposition in the HCO3─ solutions was significant on some occasions, and Fe catalyzed decomposition was the most significant contributor in both pulp slurries and pulp-free solutions.