Inorganic Salts Modulate Spontaneous Interfacial H₂O₂ Formation in Surfactant-Containing Atmospheric Droplets

Area of Science:

• Atmospheric chemistry
• Physical chemistry
• Surface science

Background:

• Hydrogen peroxide (H2O2) forms spontaneously at air-water interfaces.
• The regulation of H2O2 formation in atmospheric droplets with surfactants is not well understood.

Purpose of the Study:

• To investigate the influence of nonanoic acid (NA), a fatty acid surfactant, on interfacial H2O2 formation.
• To examine the combined effects of inorganic salts and surfactants on H2O2 production in atmospheric droplets.

Main Methods:

• Gas-nebulization method to generate droplets containing NA.
• Systematic examination of H2O2 formation with varying NA and inorganic salt concentrations.
• Ab initio molecular dynamics simulations to elucidate molecular mechanisms.

Main Results:

• Increased NA concentration slightly suppressed H2O2 production by scavenging hydroxyl radicals (•OH).
• Inorganic salts induced a "V-shaped" trend in H2O2 production with concentration, mirroring surface tension changes.
• Salt-induced deeper anchoring of NA headgroups enhanced interfacial NA concentration and suppressed H2O2 formation.

Conclusions:

• Spontaneous H2O2 formation at droplet interfaces is governed by coupled effects of inorganic salts and surfactants.
• The observed "V-shaped" salt response is dependent on surfactant headgroup properties, particularly hydrogen bonding capacity.
• Findings highlight the importance of considering coexisting salts and surfactants in atmospheric aerosol chemistry.