Highly oxidized products from the atmospheric reaction of hydroxyl radicals with toluene

Abstract Simple aromatics, largely toluene (C 7 H 8 ) and benzene (C 6 H 6 ), are emitted into Earth´s atmosphere by different sources. Their degradation initiated by the gas-phase reaction with hydroxyl radicals (OH) forms mainly bicyclic peroxy radicals (BCP) besides phenol-type compounds. The formation of highly oxidized products with at least 6 O atoms (HOMs) starting from BCP is currently controversial. Here, the experimental observation of HOMs and other products is reported for near-atmospheric conditions focusing on OH + toluene. Autoxidation processes starting from BCP generate C 7 H 9 O 7 and C 7 H 9 O 9 radicals with molar yields of $${0.25}_{\,-0.13}^{\,+0.25}\, \%$$ 0.25 − 0.13 + 0.25 % and $${0.12}_{\,-0.06}^{\,+0.12}\, \%$$ 0.12 − 0.06 + 0.12 % , respectively. Labeling experiments revealed that the ring H atoms are involved in autoxidation. The atmospherically relevant reaction of C 7 H 9 O 7 and C 7 H 9 O 9 with NO almost exclusively forms organic nitrates as HOM products, C 7 H 9 O 6-8 NO 2 , with a total molar yield ≤ 0.1%. Other HOMs, such as C 7 H 8 O 8 and C 7 H 8 O 10 , represent only small trace products. Results from OH + benzene confirmed the findings from the toluene system pointing to a minor relevance of both aromatics for HOM generation.