Allyl alcohol (AA) is the simplest unsaturated alcohol. Ozonolysis is one of the key removal processes for AA in the atmosphere. However, a recent theoretical study suggests that the ozonolysis of AA cannot feasibly occur in atmospheric conditions because of the high barrier (96 kcal/mol) involved in the primary ozonide (POZ) decomposition. In this work, the ozonolysis mechanism of AA was reinvestigated theoretically. The computed barrier for POZ decomposition is only 20 kcal/mol. Therefore, the AA ozonolysis can take place in the atmosphere, consistent with the experimental conclusions. Moreover, two new Criegee intermediates (syn-and anti-AA-CI) were found to be produced in this reaction. The wave function analyses indicate that there exists an intermolecular hydrogen bond in syn-AA-CI, which significantly affects its unimolecular decomposition and reactions with H 2 O. Compared with the normal reactions of anti-CI-AA, the stabilized syn-AA-CI has two distinct isomerization channels: (i) addition of OH group to the reactive sites of CI forming an ethylene oxide (HOOCH 2 OCH 2) and (ii) double H-transfer producing HOOCH 2 CHO. Meanwhile, the addition of H 2 O in syn-AA-CI also exhibits two different pathways. One is the unique addition-coupled double H-transfer, and the other is the additioncoupled single H-transfer, both leading to the formation of CH 2 (OH)CH(OH)OOH.