Ions and Charged Aerosol Particles in a Native Australian Eucalypt Forest
We measured atmospheric ion and charged particle concentrations and biogenic aerosol formation with an Air Ion Spectrometer (AIS) in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measured size range was 0.34–40 nm. Daytime aerosol formation took place on 52% of days with acceptable data. This is approximately twice as often as in a pine forest in Hyytiälä, southern Finland. Possible reasons are the lack of a cold, dark winter which would suppress precursor concentrations and photochemical reactions; weather that is generally drier and sunnier than in Finland; and weaker anthropogenic influence which leads to lower average background concentrations of aerosols. Average growth rates (GR) for 1.3–3 nm and 3–7 nm particles were the same as in Hyytiälä but the 7–20 nm particles grew 50% faster in Tumbarumba than in Hyytiälä. Also, unlike in Hyytiälä, organic vapours are abundant all year round in Tumbarumba so no clear seasonality was evident in GR. Average cluster (0.34–1.8 nm) and intermediate ion (1.8–7.5 nm) concentrations were about 2–4 times those in Hyytiälä which is probably the result of Tumbarumba’s high radon concentrations. A new phenomenon, nocturnal formation of aerosols (NF), appeared in summer, peaked in autumn, and gradually weakened towards winter. NF lead to intermediate and negative large ion volume concentrations twice as high as during normal daytime events. Therefore it appears that in summer and autumn, nocturnal production was the major aerosol formation mechanism in Tumbarumba.
Keywords Biogenic aerosol formation, atmospheric ions, eucalypt forest, nucleation
KeywordsDioxide Radon Carol Pasi
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