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Updated: Aug 15, 2026
13:09
Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations
Published on: January 4, 2018
Size-Dependent Reaction Pathways in Multiphase SO2 Oxidation Chemistry
Kedong Gong1, Adriane Tam1, V Faye McNeill2,3
1Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093, United States.
Environmental Science & Technology Letters
|August 14, 2026
Summary
Sulfur dioxide (SO2) uptake and oxidation in atmospheric aerosols differ by droplet size. Smaller aerosols become uptake-limited, favoring surface oxidation, while larger ones follow bulk-phase chemistry.
Area of Science:
- Atmospheric chemistry
- Aerosol science
- Environmental science
Background:
- Atmospheric sulfur dioxide (SO2) chemistry traditionally assumes bulk aqueous-phase reactions.
- This involves SO2 uptake followed by oxidation, forming sulfur(IV) (S-(IV)).
Purpose of the Study:
- To decouple SO2 uptake and S-(IV) oxidation at the single-droplet level.
- To investigate the influence of microdroplet size on these processes.
Main Methods:
- Comparing SO2 uptake and S-(IV) oxidation in microdroplets of varying sizes.
- Analyzing size-dependent mechanistic transitions using Mn-(II)-catalyzed reactions in Na2SO3 microdroplets.
Main Results:
- SO2 uptake is suppressed in smaller microdroplets, while S-(IV) oxidation is enhanced.
- SO2 uptake is 1-2 orders of magnitude slower than S-(IV) oxidation for aerosols with radii < 5 μm.
- Smaller aerosols become uptake-limited, favoring surface oxidation.
Conclusions:
- Droplet size modulates the rate-limiting step in multiphase SO2 chemistry.
- Different size dependencies in reaction steps lead to distinct oxidation mechanisms.
- The air-water interface plays a critical role in atmospheric multiphase chemistry.
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