Air ion balance in a boreal forest

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http://urn.fi/URN:NBN:fi-fe2017112251517
Title: Air ion balance in a boreal forest
Author: Chen, Xuemeng
Other contributor: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Fysiikan laitos
University of Helsinki, Faculty of Science, Department of Physics
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för fysik
Publisher: Helsingfors universitet
Date: 2014
Language: eng
URI: http://urn.fi/URN:NBN:fi-fe2017112251517
http://hdl.handle.net/10138/230330
Thesis level: master's thesis
Discipline: Physics
Fysiikka
Fysik
Abstract: The study of air ions by applying air balance concept based on the Hyytiälä SMEAR II station measurement was performed in this work. Diurnal and seasonal variations in ion concentration and environmental ionizing radiation were studied by analysing data collected from long-term measurements. Total gamma radiation was the main source for ion production in the atmosphere, which can be attenuated by snow cover during winter periods. α and β emissions from radon decay process showed a share of about 20% in the production of total ion pairs, which were sensitive to variations in soil conditions. In general, more positive ions than the negative ones exist at ground level due to the earth electrode effect. Similar patterns were found in cluster ion concentration and the ion source rate derived from the total gamma radiation. On days with new particle formation (NPF), a relation was observed between cluster ion concentration, wind speed, temperature (T) as well as relative humidity (RH). A similar connection was also identified in ion source rate and ion production rate to T and RH. A high ion source rate derived from gamma dose rate was observed on non-event days and low on NPF days. The reversed case was found in the source rate derived from radon decay emissions. The ion production rate was typically higher on NPF event days than on non-event days. Two approaches were carried out in the determination of the ion production rate in the cluster size range by using an improved balance equation of air ions. The similar values obtained using these two approaches imply a balanced condition between ionizing source and the observed ion concentration. This suggests that measurement of air ions by the Balanced Scanning Mobility Analyser (BSMA) is likely to be reliable, though accurate parameterization for sub-0.8 nm ions is not available to the present knowledge. Moreover, the ion production rate and formation rate were found incomparable.


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