Growth and Shrinkage of New Particles in the Atmosphere in Hong Kong

Abstract

Grown nucleated particles > 50 nm in diameter are an important source of cloud condensation nuclei (CCN) and when the size is > 100 nm, they can also have direct influence on the climate. In this study, the nucleation and growth of new particles in the atmosphere in Hong Kong were investigated during dry season (monthly averaged RH < 75%). The maximum size of grown nucleated particles was generally less than 40 nm during new particle burst and growth events. The exception, accounting for ∼ 20% of all burst and growth events, was those induced by strong photochemical reactions, in which subsequent particle shrinkage occurred. Temporal particle and gas concentration variability and meteorological conditions support the occurrence of particle shrinkage. The shrinkage rate calculated (∼ 8 nm h^–1) was close to the growth rate. The observation of particle shrinkage sheds new light on particle transformation dynamics and it would add to the understanding of particle behavior in the atmosphere.

Acknowledgments

This work was supported by the Hong Kong Jockey Club Charities Trust. XHY would like to acknowledge the support of NSFC No. 40775082 and thanks Guangliang Liu and Fan Yang for their help on preparing figures.

Notes

*Formation rate of < 30 nm particles was corrected for particle-particle coagulation effect using the same method by Qian et al. (2007)

**Regime 1 and Regime 2 overlapped and the rate cannot be estimated.