Nitrous oxide (N₂O), a significant contributor to the greenhouse effect, is generated during the biological nutrient removal in wastewater treatment plants (WWTPs). Developing mathematical models estimating the N₂O dynamics under changing operational conditions (e.g. dissolved oxygen, DO) is essential to design mitigation strategies. Based on the activated sludge models (ASM) structure, this work presents an ASM2d-N₂O model including all the biological N₂O production pathways for a municipal anaerobic/anoxic/oxic (A²/O) WWTP with biological removal of organic matter, nitrogen and phosphorus, and its application in different dynamic scenarios. Three microbial N₂O production pathways were considered: nitrifier denitrification, hydroxylamine oxidation, and heterotrophic denitrification, with the first two being activated by ammonia oxidizing bacteria (AOB). A stripping effectivity (SE) coefficient was added to reflect the non-ideality of the stripping model. Partial nitrification and high N₂O production via nitrifier denitrification were observed when the range of DO in the aerobic compartment was 1.8 to 2.5 mg·L⁻¹. It could imply that low aeration strategies lead to low overall carbon footprint provided complete nitrification is not hindered. The model predicted high N₂O emissions when low DO (∼1.1 mg L⁻¹) and high ammonium concentration concurred. With the AOB prevailing over the nitrite oxidizing bacteria (NOB), nitrite was accumulated, triggering the activation of the nitrifier denitrification pathway. After suddenly increasing the influent ammonium load, the AOB had a greater growth compared to the NOB and the same pathway was considered as N₂O hotspot. Especially under conditions promoting partial nitrification (i.e. low DO) and raising the stripping effect importance (i.e. high SEs), the highest N₂O emission factors were predicted.