Atmospheric Hydroxyl Radical Source: Reaction of Triplet SO2 and Water

The reaction of electronically excited triplet state sulfur dioxide ((SO2)-S-3) 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 (SO2)-S-3, making it a suitable probe of OH production from the reaction of (SO2)-S-3 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 (O-2) or ozone (O-3) present.