Abstract
Abstract. The charging state of aerosol populations was determined using an Ion-DMPS in Helsinki, Finland between December 2008 and February 2010. We extrapolated the charging state and calculated the ion-induced nucleation fraction to be around 1.3 % ± 0.4 % at 2 nm and 1.3 % ± 0.5 % at 1.5 nm, on average. We present a new method to retrieve the average charging state for a new particle formation event, at a given size and polarity. We improve the uncertainty assessment and fitting technique used previously with an Ion-DMPS. We also use a new theoretical framework that allows for different concentrations of small ions for different polarities (polarity asymmetry). We extrapolate the ion-induced fraction using polarity symmetry and asymmetry. Finally, a method to calculate the growth rates from the behaviour of the charging state as a function of the particle diameter using polarity symmetry and asymmetry is presented and used on a selection of new particle formation events.
Highlights
The amount of particulate matter suspended in the air and its size distribution influence the Earth’s climate and precipitation patterns (e.g. Twomey, 1991; Lohmann and Feichter, 2005; Myhre et al, 2009; Stevens and Feingold, 2009)
For example due to missing data, it is Each day of the measurement period was examined in search desirable to estimate the growth rate from only either nega- of new particle formation events
There were no measurements made with the IonDMPS during the summer
Summary
The amount of particulate matter suspended in the air (aerosol) and its size distribution influence the Earth’s climate and precipitation patterns (e.g. Twomey, 1991; Lohmann and Feichter, 2005; Myhre et al, 2009; Stevens and Feingold, 2009). Twomey, 1991; Lohmann and Feichter, 2005; Myhre et al, 2009; Stevens and Feingold, 2009). These particles can be emitted into the atmosphere directly (primary aerosols) or nucleate and grow in the atmosphere (secondary aerosols). The latter is commonly called new particle formation (NPF) and growth. New particle formation has been observed in a wide range of environments, and takes place frequently The frequency and the mechanisms involved in new particle formation depend on the type of environment where it takes place. The phenomenon has been observed to take place on almost every sunny day in the African Savannah (Laakso et al, 2008) whereas it is observed on about every third day in the Finnish boreal forest (Dal Maso et al, 2005) but almost never in the Amazon rain forest (Ahlm et al, 2010)
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