Atmospheric Hydroxyl Radical Source: Reaction of Triplet SO2 and Water.

The reaction of electronically excited triplet state sulfur dioxide (3SO2) with water was investigated both theoretically and experimentally. The quantum chemical calculations find that the reaction leads to the formation of hydroxyl radical (OH) and hydroxysulfinyl radical (HOSO) via a low energy barrier pathway. Experimentally the formation of OH was monitored via its reaction with methane, which itself is relatively unreactive with 3SO2, making it a suitable probe of OH production from the reaction of 3SO2 and water. This reaction has implications for the formation of OH in environments that are assumed to be depleted in OH, such as volcanic plumes. This reaction also provides a mechanism for the formation of OH in planetary atmospheres with little or no oxygen (O2) or ozone (O3) present.