Organic Aerosol Formation Mechanisms and Characterization

Organic aerosols are a complex mixture of carbon-based particles suspended in the atmosphere. They arise from direct emissions of biological or anthropogenic materials (primary organic aerosol) and from the oxidation of volatile organic compounds (secondary organic aerosol, SOA). Secondary formation often involves reactions with oxidants such as ozone, hydroxyl radicals and nitrate radicals, leading to functionalisation and oligomerisation processes that reduce volatility and promote partitioning into the particulate phase. Characterisation techniques such as one- and multidimensional liquid chromatography coupled with high-resolution mass spectrometry have enabled detailed molecular-level insights into this complexity. Gas-phase mechanisms involving Criegee intermediates and radical pathways compete with heterogeneous processes in the particle or aqueous phase, where further ageing can alter oxidation state, volatility and hygroscopicity. These physicochemical transformations influence climate via scattering and absorption of solar radiation, affect cloud condensation nuclei activity and impact human health through respiratory exposure. A global perspective now links emission inventories, advanced analytical measurements and kinetic modelling to quantify formation pathways, composition dynamics and the role of organic aerosols in atmospheric processes.

Research from Nature Portfolio

Enhanced organic mass from volatile emissions has been shown to drive oligomer formation in atmospheric aerosols. Foundational observations reveal that increased secondary organic aerosol loading correlates with higher concentrations of oligomeric compounds, which significantly affect cloud condensation nuclei activity. This work clarifies how rising biogenic volatile organic compound emissions under warming climates can alter the oligomer content and composition of ambient organic aerosols, with important feedbacks for aerosol–cloud interactions and climate model predictions.

Organic Aerosol Formation Mechanisms and Characterization publication trend

The graph below shows the total number of articles in organic aerosol formation mechanisms and characterization across all publications each year (not limited to Nature Index journals).

Technical terms

Primary organic aerosol (POA): Particles directly emitted into the atmosphere from sources such as vegetation, combustion or sea spray.

Secondary organic aerosol (SOA): Particles formed in the atmosphere by gas-phase oxidation of volatile organic compounds followed by partitioning of the products into the particulate phase.

Oligomer: High-molecular-weight compound formed by the covalent linkage of smaller oxidation products, contributing to low volatility and aerosol mass.

Hydroxyl radical (OH): A highly reactive atmospheric oxidant that initiates gas-phase oxidation of organic molecules and drives ageing processes in both gas and aqueous phases.

Criegee intermediate: Short-lived carbonyl oxide species formed during ozonolysis that can undergo further reactions leading to functionalised or oligomeric products.

Cloud condensation nucleus (CCN): Particle that can act as a seed for cloud droplet formation when supersaturated water vapour condenses upon it.

References

1. Characterisation of atmospheric organic aerosols with one- and multidimensional liquid chromatography and mass spectrometry: State of the art and future perspectives. TrAC Trends in Analytical Chemistry (2024).
2. Aging of α‑Pinene Secondary Organic Aerosol by Hydroxyl Radicals in the Aqueous Phase: Kinetics and Products. Environmental Science and Technology (2023).
3. Enhanced Volatile Organic Compounds emissions and organic aerosol mass increase the oligomer content of atmospheric aerosols. Scientific Reports (2016).