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RESEARCH ARTICLE
Contents Vol 6(6)

Postfrontal nanoparticles at Cape Grim: observations

John L. Gras A E , Salah I. Jimi B C , Steven T. Siems C D and Paul B. Krummel A
+ Author Affiliations
- Author Affiliations

A Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, 107–121 Station St., Aspendale, Vic. 3195, Australia.

B School of Geography and Environmental Science, Monash University, Clayton, Vic. 3800, Australia.

C Climate Theme Monash Sustainability Institute, Monash University, Clayton, Vic. 3800, Australia.

D School of Mathematical Sciences, Monash University, Clayton, Vic. 3800, Australia.

E Corresponding author. Email: john.gras@csiro.au

Environmental Chemistry 6(6) 508-514 https://doi.org/10.1071/EN09075
Submitted: 22 June 2009  Accepted: 28 October 2009   Published: 18 December 2009

Environmental context. Clouds and the factors controlling cloud properties are essential components in understanding and accurately predicting global climate change. This work examines nanometre-sized atmospheric particles, particularly bursts of enhanced particle concentrations following cold fronts over the Southern Ocean. The properties of these events have been established to enable modelling of their significance as a source of cloud-droplet-forming nuclei.

Abstract. Nanoparticles (diameter <10 nm) were studied in clean maritime air at Cape Grim over a 2-year period. Concentrations were determined using a condensation nucleus counter (CNC) and an ultra-CNC (UCNC), requiring careful treatment of drifts in counter efficiency. This is the first extended examination of nanoparticles following cold fronts and shows that nanoparticle enhancements were present following 94% of 121 cold fronts studied. Typical enhancements were ~100 cm–3 with maxima ~300–500 cm–3, occur 9–11 h after the front and contain multiple peaks with peak-to-peak separation of 8–11 h. Most enhancements were associated with drier conditions, indicative of increased entrainment of free-tropospheric air after the front. The quasi-periodicity of the enhancements may be related to mesoscale structures in cloud fields following fronts but this requires testing. This quantification of event properties allows evaluation of the significance of these events for the cloud nucleating particle (CCN) population.

Additional keywords: CCN, marine aerosol, nucleation.


Acknowledgements

We acknowledge the effort of the staff at the Cape Grim Baseline Air Pollution Station in running and maintaining all instruments in the Particle Program, and also acknowledge funding for this work from the Australian Bureau of Meteorology and CSIRO.


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