Global Impacts of Simulating Organic Aerosol Phase State

Area of Science:

• Atmospheric Chemistry and Physics
• Aerosol Science
• Climate Modeling

Background:

• Atmospheric organic aerosol (OA) exists in multiple physical states (liquid, semisolid, solid), influenced by molecular properties and environmental factors.
• Current atmospheric models predominantly assume OA is exclusively in the liquid phase, neglecting the impact of its phase state on key processes.
• This simplification may lead to inaccuracies in predicting OA behavior, atmospheric transport, and climate effects.

Purpose of the Study:

• To develop and implement a source-specific organic aerosol (OA) phase-state model.
• To investigate the phase-state-dependent nature of heterogeneous processes like gas-particle partitioning, reactive uptake, and ice nucleation.
• To quantify the impact of OA phase state on global OA concentrations, vertical profiles, and the atmospheric OA burden.

Main Methods:

• Development of a novel OA phase-state model considering liquid, semisolid, and solid states.
• Integration of phase-state-dependent parameterizations for gas-particle partitioning and reactive uptake.
• Simulation of heterogeneous processes including ice particle nucleation by solid-state OA.
• Comparison of model outputs with observational data from aircraft campaigns (EMERGE-AS, ATom).

Main Results:

• Global simulations indicate over 70% of surface OA exists in a semisolid state, aligning with observational data.
• OA viscosity increases with altitude and is higher in continental midlatitude regions, with minimal liquid phase OA above 2.5 km.
• The OA phase state significantly alters gas-particle partitioning and reactive uptake rates, and enhances OA removal at higher altitudes.
• Model simulations show a 28% decrease in surface OA concentrations and an 8% increase at 7 km, reducing the vertical gradient by 36%.

Conclusions:

• The phase state of organic aerosol is a critical factor influencing atmospheric processes and should be explicitly included in models.
• Accounting for OA phase state improves the accuracy of simulated OA vertical profiles, particularly in near-source and remote regions.
• The findings suggest a revised understanding of OA's role in atmospheric chemistry, aerosol-cloud interactions, and climate forcing.