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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-156
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Mar 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Observations of Particles at their Formation Sizes in Beijing, China
Rohan Jayaratne1, Buddhi Pushpawela1, Congrong He1, Jian Gao2, Li Hui2, and Lidia Morawska1 1International Laboratory for Air Quality and Health, Queensland University of Technology, GPO Box 2434, Brisbane 4001, Australia
2Chinese Research Academy of Environmental Sciences, Beijing 100012, China
Abstract. New particle formation (NPF) has been observed in many highly polluted environments of South-East Asia, including Beijing, where the extent of its contribution to intense haze events is still an open question. Estimated characteristics of NPF events, such as their starting times and formation and growth rates of particles, are very different when the measurements are restricted to particles in larger size ranges. In order to understand the very first steps of particle formation, we used a neutral cluster and air ion spectrometer (NAIS) to investigate particle characteristics at sizes exactly where atmospheric nucleation and cluster activity occurs. Observations over a continuous three-month period in Beijing showed 26 NPF events. These events generally coincided with periods with relatively clean air when the wind direction was from the less-industrialized north. No NPF were observed when the daily mean PM2.5 concentration exceeded 43 µg m-3, which was the upper threshold for particle formation in Beijing. The fraction of particles that are charged in the size range 2–42 nm was normally about 15%. However, this fraction increased to 20–30% during haze events and decreased to below 10 % during NPF events. With the NAIS, we determined the starting times of NPF very precisely to a greater accuracy than has been possible in Beijing before and provided a temporal distribution of NPF events with a maximum at about 8.30 am. Particle formation rates varied between 10–36 cm-3 s-1. Particle growth rates were estimated to be in the range 0.5–9.0 nm h-1. These results are more reliable than previous studies in Beijing as the measurements were conducted for the first time at the exact sizes where clusters form into particles and provide useful insight into the formation of haze events.

Citation: Jayaratne, R., Pushpawela, B., He, C., Gao, J., Hui, L., and Morawska, L.: Observations of Particles at their Formation Sizes in Beijing, China, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-156, in review, 2017.
Rohan Jayaratne et al.
Rohan Jayaratne et al.

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Short summary
Observations over a continuous three-month period in Beijing showed 26 new particle formation (NPF) events, generally coincided with periods with relatively clean air when the wind direction was from the less-industrialized north. Large particles in the atmosphere suppress the gaseous supersaturation that is required for NPF. No events were observed when the daily mean PM2.5 concentration exceeded 43 µg m-3. These results provide useful insight into the formation of haze events in mega cities.
Observations over a continuous three-month period in Beijing showed 26 new particle formation...
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