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How new particles are formed in polluted urban environments with high pre-existing aerosol population


During intense NPF events in wintertime Beijing, sulfuric acid together with base stabilizers drove the formation of nano clusters. Oxidized organic molecules were crucial for particle growth above 2–3 nm, enabling the growth into climate‐ and health‐relevant sizes.

In order to control ambient aerosol number, these key compounds need to be monitored and regulated.


New particle formation (NPF) happens in all environments. Even in polluted megacities. An international team of scientists conducted comprehensive measurements in downtown Beijing in winter 2018. They measured a wide range of atmospheric gaseous species that contribute to new particle formation, particle size distribution of 1 nm–10 μm aerosol particles, and used instruments that allow molecular‐level analyses of the process: this included analyses of sulfuric acid cluster composition and budget and chemical and physical properties of oxidized organic molecules (OOMs)

They concluded that during the measurement campaign the initial nano cluster aerosol were thermodynamically stable sulfuric acid clusters of about 1–1.5 nm. This particle formation process in wintertime Beijing is driven by the acid‐base clustering mechanism in the presence of abundant stabilizers, such as amines and ammonia (NH3). They further showed that the availability of sulfuric acid (H2SO4) defines the intensity of the initial steps of new particle formation.

Contrary to recent chamber studies the majority of condensable oxidized organic molecules had a minor contribution to the formation of new particles but were crucial for particle growth into larger sizes.

“This synergistic role of H2SO4, base species, and OOMs in NPF is likely representative of polluted urban environments where abundant H2SO4 and base species usually co‐exist, and OOMs are with moderately low volatility when produced under high NOx concentrations.”


To learn more details of this exciting research, please read the open access publication by Chao Yan and 62 international colleagues in Geophysical Research Letters:

The Synergistic Role of Sulfuric Acid, Bases, and Oxidized Organics Governing New‐Particle Formation in Beijing


To learn more about the A11 nCNC (PSM) system that was used for these measurements, please visit


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