Vapor-wall deposition in chambers: theoretical considerations

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Environmental Science

Background:

• Laboratory chamber studies are crucial for understanding secondary organic aerosol (SOA) formation.
• Vapor-wall deposition is a known artifact in chamber experiments that can influence measured SOA yields.
• The role of kinetic limitations in SOA formation and their interplay with chamber artifacts require further investigation.

Purpose of the Study:

• To investigate the influence of vapor-wall deposition and kinetic limitations on secondary organic aerosol (SOA) yields.
• To determine the conditions under which seed aerosol surface area affects SOA yield measurements.
• To provide a framework for accurately extrapolating laboratory-derived SOA yields to atmospheric conditions.

Main Methods:

• Utilized a coupled vapor-particle dynamics model to simulate toluene oxidation experiments.
• Varied seed aerosol surface area in model simulations to mimic laboratory conditions.
• Compared characteristic time scales of gas-phase reaction, vapor-wall deposition, and gas-particle equilibration.

Main Results:

• A seed surface area dependence of the SOA yield was observed only when the condensation of vapors onto particles was kinetically limited.
• The existence of kinetic limitation was predictable by comparing relevant time scales.
• Vapor-wall deposition was found to consistently depress SOA yields, irrespective of kinetic limitations.

Conclusions:

• The observed increase in SOA yield with seed surface area in laboratory chambers is primarily due to kinetic limitations in vapor condensation, not solely vapor-wall deposition.
• Accurate extrapolation of chamber-derived SOA yields to the atmosphere requires accounting for both vapor-wall deposition and kinetic limitations.
• Understanding gas-particle equilibration, influenced by the accommodation coefficient (αp), is vital for assessing kinetic limitations.