14 Apr 2022
14 Apr 2022
Status: this preprint is currently under review for the journal ACP.

The effectiveness of coagulation sink of 3–10 nm atmospheric particles

Runlong Cai1, Ella Häkkinen1, Chao Yan1,2, Jingkun Jiang3, Markku Kulmala1,2, and Juha Kangasluoma1,4 Runlong Cai et al.
  • 1Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Helsinki, 00014, Finland
  • 2Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China
  • 3State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China
  • 4Karsa Ltd., A. I. Virtasen aukio 1, Helsinki, 00560, Finland

Abstract. As a major source of ultrafine particles, new particle formation (NPF) occurs frequently in various environments. However, the survival of new particles and the frequent occurrence of NPF events in polluted environments have long been perplexing, since new particles are expected to be scavenged by high coagulation sinks. Towards solving these problems, we establish an experimental method and directly measure the effectiveness of the size-dependent coagulation sink of monodisperse 3–10 nm particles in well-controlled chamber experiments. Based on the chamber experiments and long-term atmospheric measurements from Beijing, we then discuss the survival of new particles in polluted environments. In the chamber experiments, the measured coagulation coefficient increases significantly with a decreasing particle size, whereas it is not sensitive to the compositions of test particles. Comparison between the measured coefficient with theoretical predictions shows that almost every coagulation leads to the scavenging of one particle, and the coagulation sink exceeds the hard-sphere kinetic limit due to van der Waals attractive force. For urban Beijing, the effectiveness of coagulation sink and a moderate or high (e.g., > 3 nm h-1) growth rate of new particles can explain the occurrence of measured NPF events; the moderate growth rate further implies that in addition to gaseous sulfuric acid, other gaseous precursors also contribute to the growth of new particles.

Runlong Cai et al.

Status: open (until 24 Jun 2022)

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Runlong Cai et al.

Runlong Cai et al.


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Short summary
The influences of new particle formation on the climate and air quality are governed by particle survival, which has been under debate due to the uncertainties in the coagulation sink. Here we measure the coagulation coefficient of sub-10 nm particles and demonstrate that collisions between the freshly nucleated and background particles can effectively lead to coagulation. We further show that the effective coagulation sink is consistent with the new particle formation measured in urban Beijing.