Chemical Ionization Mass Spectrometry in Atmospheric Organic Aerosol Dynamics

Chemical ionization mass spectrometry (CI-MS) has emerged as a pivotal analytical technique for probing the formation, growth and transformation of organic aerosol in the atmosphere. By selectively ionizing target species under gentle conditions, CI-MS enables real-time detection of extremely low-volatility oxidation products and transient intermediates that drive new particle formation and secondary organic aerosol (SOA) growth. Through high mass resolution and time-resolved profiling, this approach deciphers complex reaction pathways—autoxidation of volatile organic compounds, inter-radical accretion and organonitrate formation—across laboratory chambers, ground-based observatories and airborne platforms. The insights gained inform atmospheric models on aerosol-cloud interactions, radiative forcing and air quality, underpinning strategies for pollution mitigation and climate predictions. CI-MS therefore serves as a bridge between molecular-level chemistry and global aerosol dynamics, fostering advances in both fundamental understanding and practical applications.

Research from Nature Portfolio

Recent studies have employed airborne CI-MS to characterise new particle formation in the tropical upper troposphere. Measurements reveal that extremely low-volatility organonitrates derived from biogenic isoprene oxidation, in concert with nitrogen oxides from lightning, initiate nucleation bursts and supply cloud condensation nuclei on a continental scale.

Dedicated laboratory experiments have demonstrated that trace levels of nitrogen monoxide can boost the yield of highly oxygenated organic molecules during monoterpene oxidation. By modulating peroxy radical pathways, low-pptv NO concentrations favour alkoxy radical isomerisation and sustain secondary organic aerosol formation even in pristine, low-NO environments.

Foundational field and chamber work has shown that hydroxyl radical reactions with biogenic hydrocarbons yield multifunctional, highly oxidised products via rapid autoxidation. The unexpectedly high product yields, supported by real-world observations, have refined our understanding of the diurnal cycle of secondary organic aerosol generation.

Chemical Ionization Mass Spectrometry in Atmospheric Organic Aerosol Dynamics publication trend

The graph below shows the total number of articles in chemical ionization mass spectrometry in atmospheric organic aerosol dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Chemical ionization mass spectrometry (CI-MS): A soft ionisation technique that gently charges molecules for mass analysis, preserving fragile oxidation products.

Secondary organic aerosol (SOA): Particulate matter formed in the atmosphere via gas-phase oxidation of volatile organic compounds and subsequent condensation.

New particle formation (NPF): The nucleation of molecular clusters in the atmosphere that grow into aerosol particles through vapour condensation.

Highly oxygenated organic molecule (HOM): A low-volatility oxidation product containing multiple oxygen functional groups, crucial for aerosol nucleation and growth.

Organic peroxy radical (RO2): Reactive intermediate formed during VOC oxidation that undergoes autoxidation or cross-reaction pathways leading to HOMs and accretion products.

Organonitrate: Nitrogen-containing oxidation product of VOCs that contributes to particle mass and influences aerosol-cloud interactions.

References

1. Isoprene nitrates drive new particle formation in Amazon’s upper troposphere. Nature (2024).
2. NO at low concentration can enhance the formation of highly oxygenated biogenic molecules in the atmosphere. Nature Communications (2023).
3. Hydroxyl radical-induced formation of highly oxidized organic compounds. Nature Communications (2016).
4. Large Gas-Phase Source of Esters and Other Accretion Products in the Atmosphere. Journal of the American Chemical Society (2023).
5. Decomposition of Clusters of Oxygenated Compounds with NO3 – by Applying Voltage Scanning to Chemical Ionization Mass Spectrometry in Steady-State Experiments. Environmental Science & Technology Letters (2024).
6. Data‐Driven Compound Identification in Atmospheric Mass Spectrometry. Advanced Science (2023).
7. Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol. Chemical Reviews (2019).