Rapid Sulfate Formation via Uncatalyzed Autoxidation of Sulfur Dioxide in Aerosol Microdroplets.
Environ Sci Technol
; 56(12): 7637-7646, 2022 06 21.
Article
in En
| MEDLINE
| ID: mdl-35638231
ABSTRACT
Severe winter haze events in Beijing and North China Plain are characterized by rapid production of sulfate aerosols with unresolved mechanisms. Oxidation of SO2 by O2 in the absence of metal catalysts (uncatalyzed autoxidation) represents the most ubiquitous SO2 conversion pathway in the atmosphere. However, this reaction has long been regarded as too slow to be atmospherically meaningful. This traditional view was based on the kinetic studies conducted in bulk dilute solutions that mimic cloudwater but deviate from urban aerosols. Here, we directly measure the sulfate formation rate via uncatalyzed SO2 autoxidation in single (NH4)2SO4 microdroplets, by using an aerosol optical tweezer coupled with a cavity-enhanced Raman spectroscopy technique. We find that the aqueous reaction of uncatalyzed SO2 autoxidation is accelerated by two orders of magnitude at the high ionic strength (â¼36 molal) conditions in the supersaturated aerosol water. Furthermore, at acidic conditions (pH 3.5-4.5), uncatalyzed autoxidation predominately occurs on droplet surface, with a reaction rate unconstrained by SO2 solubility. With these rate enhancements, we estimate that the uncatalyzed SO2 autoxidation in aerosols can produce sulfate at a rate up to 0.20 µg m-3 hr-1, under the winter air pollution condition in Beijing.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Sulfur Dioxide
/
Air Pollutants
Country/Region as subject:
Asia
Language:
En
Journal:
Environ Sci Technol
Year:
2022
Document type:
Article
Affiliation country:
China