Volatility Dynamics of Atmospheric Organic Aerosols

The volatility of atmospheric organic aerosols governs their phase partitioning, evolution and impact on climate, air quality and human health. Organic compounds emitted directly or formed by gas‐phase oxidation span a wide spectrum of saturation concentrations, from highly volatile gases that remain in the vapour phase to extremely low volatility components that persist in particles. Temperature, relative humidity and the degree of chemical oxidation alter volatility distributions, driving evaporation, condensation and oligomerisation processes. Dynamic mass transfer is controlled by factors such as the mass accommodation coefficient and diffusion within particles, influencing timescales of gas‐particle equilibration and the growth or shrinkage of particulate matter. Modelling frameworks, including the volatility basis set and two‐dimensional volatility‐oxidation schemes, represent complex mixtures by grouping organics into defined volatility bins. Measurements using thermodenuders, chamber experiments and field deployable mass spectrometers have revealed that semi‐volatile and low‐volatility organics often dominate ambient aerosol mass and that rapid mixing can occur within minutes. A thorough understanding of volatility dynamics underpins accurate predictions of aerosol lifetimes, secondary organic aerosol yields and radiative effects, and guides strategies to mitigate particulate pollution on regional and global scales.

Research from Nature Portfolio

Recent studies have deployed controlled‐chamber mass spectrometry to quantify the dynamic partitioning of representative organic vapours into seed particles under atmospherically relevant humidity and composition. These experiments report mass accommodation coefficients approaching unity and demonstrate equilibration times on the order of a few minutes, indicating that mass transfer limitations play a smaller role than previously assumed. The findings prompt revisions in the treatment of kinetic uptake in models and highlight the importance of incorporating rapid gas‐particle exchange when simulating secondary organic aerosol formation and evolution.

Volatility Dynamics of Atmospheric Organic Aerosols publication trend

The graph below shows the total number of articles in volatility dynamics of atmospheric organic aerosols across all publications each year (not limited to Nature Index journals).

Technical terms

Mass accommodation coefficient (α): The probability that a gas‐phase molecule colliding with a particle surface will enter and remain in the condensed phase.

Saturation concentration (C*): The vapour concentration at which an organic compound is in equilibrium between gas and particle phases, expressed in µg m⁻³.

Volatility basis set (VBS): A modelling framework that represents complex organic mixtures by grouping compounds into discrete volatility bins characterised by C* values.

Thermodenuder: An experimental device that heats an aerosol sample to evaporate volatile components and quantifies the remaining non-volatile fraction.

Secondary organic aerosol (SOA): Particulate matter formed in the atmosphere from the oxidation of volatile organic compounds, often semi-volatile in nature.

References

1. Direct measurements of semi-volatile organic compound dynamics show near-unity mass accommodation coefficients for diverse aerosols. Communications Chemistry (2019).
2. Chemically-resolved aerosol volatility measurements from two megacity field studies. Atmospheric Chemistry and Physics (2009).
3. Quantifying the volatility of organic aerosol in the southeastern US. Atmospheric Chemistry and Physics (2017).