H2S, hydrogen sulfide is a reducing species, which is relatively unstable but survives for rather a long time owing to its slow reaction with atmospheric oxygen. This sulfur-containing gas is a major participant in gas to particle conversion in the atmosphere. Many sulfur-containing gases are reactive and thus are rapidly converted to sulfuric acid.
[Analytical Science, 67(2); 318-323; 1995.]
Source: Atmospheric Chemistry Glossary