Sulfate Aerosol Formation Mechanisms in Atmospheric Chemistry

Sulfate aerosols arise principally from the atmospheric oxidation of sulfur dioxide (SO₂), a by-product of both natural processes and human activities. Gas-phase routes, mediated by hydroxyl radicals (OH) and ozone (O₃), initiate SO₂ conversion, but fail to account fully for observed particulate loads in polluted atmospheres. Aqueous-phase oxidation within cloud and aerosol water accommodates secondary pathways involving hydrogen peroxide (H₂O₂), nitrite/nitrous acid (NO₂/HONO) and transition metal ions. Heterogeneous reactions on particle surfaces further accelerate SO₂ uptake and lead to in-particle radical chain processes. Key controls include aerosol liquid water content, particle acidity (pH) and the availability of organosulfur precursors such as hydroxymethanesulfonate (HMS). These multiphase interactions underpin regional haze episodes, influence radiative forcing and inform strategies for air-quality management and climate mitigation.

Research from Nature Portfolio

Recent studies have quantified the global significance of aerosol-phase H₂O₂ oxidation, showing that elevated oxidant levels can counteract SO₂ emission reductions and sustain sulphate burdens across continental regions. Complementary work has demonstrated that manganese-catalysed oxidation of SO₂ on aerosol surfaces can dominate particulate sulphur production during winter haze, with surface-mediated pathways contributing the majority of observed sulphate yields under high-humidity conditions.

Sulfate Aerosol Formation Mechanisms in Atmospheric Chemistry publication trend

The graph below shows the total number of articles in sulfate aerosol formation mechanisms in atmospheric chemistry across all publications each year (not limited to Nature Index journals).

Technical terms

Sulfate Aerosol: Fine particulate sulfate (SO₄²⁻) formed primarily through oxidation of sulfur dioxide in the atmosphere.

Aqueous-phase Oxidation: Chemical transformation of dissolved sulfur species within cloud droplets or aerosol water volumes.

Heterogeneous Oxidation: Reaction occurring at the interface or within aerosol particles between gaseous precursors and condensed-phase constituents.

Hydroxymethanesulfonate (HMS): Organosulfur compound in aerosol water that can convert to inorganic sulfate upon oxidation.

Transition Metal Ion-Catalysed Oxidation: Sulfite (S(IV)) oxidation accelerated by metal ions (e.g. Mn²⁺) on particle surfaces, enhancing sulphate production.

Aerosol Liquid Water Content: Quantity of water in aerosol particles that governs the efficiency of multiphase chemical reactions.

References

1. Hydrogen peroxide serves as pivotal fountainhead for aerosol aqueous sulfate formation from a global perspective. Nature Communications (2024).
2. Significant Conversion of Organic Sulfur from Hydroxymethanesulfonate to Inorganic Sulfate and Peroxydisulfate Ions upon Heterogeneous OH Oxidation. Environmental Science & Technology Letters (2023).
3. Sulfate formation is dominated by manganese-catalyzed oxidation of SO2 on aerosol surfaces during haze events. Nature Communications (2021).
4. Aerosol high water contents favor sulfate and secondary organic aerosol formation from fossil fuel combustion emissions. npj Climate and Atmospheric Science (2023).
5. Fast sulfate formation from oxidation of SO2 by NO2 and HONO observed in Beijing haze. Nature Communications (2020).
6. Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain. Atmospheric Chemistry and Physics (2020).