The Atmospheric Puzzle: Unveiling the Enigmatic Chemistry of Sulfur Trioxide

Researchers at Tampere University have found that sulfur trioxide (SO3) can create products beyond sulfuric acid by interacting with organic and inorganic acids in the atmosphere.

These newly identified acidic sulfuric anhydride products are likely crucial in forming new atmospheric particles and incorporating carboxylic acids into nanoparticles. Improved predictions of aerosol formation could help reduce air pollution and clarify climate change impacts.

Previously, it was assumed that gaseous SO3 would rapidly convert to sulfuric acid at any reasonable humidity. However, recent findings (Yao et al.) show that significant levels of SO3 accumulate under urban pollution conditions, suggesting gaps in our understanding of its formation and loss processes.

Researchers at Tampere University and their collaborators have now demonstrated that SO3’s interaction with common atmospheric acids quickly forms acidic sulfuric anhydride molecules, which are likely very effective in forming new particles and affecting climate dynamics.

The researchers used laboratory experiments and quantum chemistry calculations to study the reaction products of SO3 with organic and inorganic acids under relevant conditions of pressure and temperature. Field measurements confirmed the relevance of these reactions in various environments, such as urban areas, marine and polar regions, and volcanic plumes.

“The acids we studied can act as effective sinks for gaseous SO3 in the atmosphere, influencing sulfuric acid concentrations and aerosol properties. These findings challenge our understanding of atmospheric chemistry by revealing new pathways for particle formation and carboxylic acid transport mechanisms,” explains Dr. Avinash Kumar, a lead author from Tampere University.

The study also reveals a direct gas-phase pathway to organosulfur compounds, impacting the sulfur content in atmospheric aerosols, which was previously thought to only originate from multiphase reactions.

“The significance of these reactions means that incorporating them into current atmospheric chemistry models will greatly enhance their reliability, particularly for understanding aerosol formation in high-sulfur regions,” adds Dr. Siddharth Iyer of Tampere University.

“Better prediction of aerosol formation can lead to more effective strategies for managing air pollution and mitigating its impact on the global climate.”