Abstract
Abstract. In this work, we examined the interaction of ions and neutral particles during atmospheric new particle formation (NPF) events. The analysis is based on simultaneous field measurements of atmospheric ions and total particles using a neutral cluster and air ion spectrometer (NAIS) across the diameter range 2–25 nm. The Waldstein research site is located in a spruce forest in NE Bavaria, Southern Germany, known for enhanced radon concentrations, presumably leading to elevated ionization rates. Our observations show that the occurrence of the ion nucleation mode preceded that of the total particle nucleation mode during all analyzed NPF events. The time difference between the appearance of 2 nm ions and 2 nm total particles was typically about 20 to 30 min. A cross correlation analysis showed a rapid decrease of the time difference between the ion and total modes during the growth process. Eventually, this time delay vanished when both ions and total particles did grow to larger diameters. Considering the growth rates of ions and total particles separately, total particles exhibited enhanced growth rates at diameters below 15 nm. This observation cannot be explained by condensation or coagulation, because these processes would act more efficiently on charged particles compared to neutral particles. To explain our observations, we propose a mechanism including recombination and attachment of continuously present cluster ions with the ion nucleation mode and the neutral nucleation mode, respectively.
Highlights
Tropospheric new particle formation (NPF) is a worldwide phenomenon (Kulmala et al, 2004a; Kulmala and Kerminen, 2008) contributing to the global particle number and total amount of cloud condensation nuclei (Makkonen et al, 2012; Merikanto et al, 2009; Spracklen et al, 2006)
We present measurements performed with the neutral cluster and air ion spectrometer (NAIS) during NPF
Simultaneous measurements of neutral and charged clusters and particles at the Waldstein ecosystem research site from 17 June to 18 August 2012 showed a frequent occurrence of new particle formation events
Summary
Tropospheric new particle formation (NPF) is a worldwide phenomenon (Kulmala et al, 2004a; Kulmala and Kerminen, 2008) contributing to the global particle number and total amount of cloud condensation nuclei (Makkonen et al, 2012; Merikanto et al, 2009; Spracklen et al, 2006). The formation of stable clusters happens in the mobility diameter (Dm) range between 1 to 2 nm. Once formed, the stable clusters are activated and experience rapid growth (Kulmala et al, 2013). Comprehensive field measurements of NPF events at different locations in Europe showed an earlier formation of charged particles compared to total particles (neutral + charged particles; Manninen et al, 2010). The ratio of charged particle concentrations to neutral particle concentrations in a defined diameter interval is defined as the charged fraction. In a bipolar ion environment, the size-dependent charged fraction of an aerosol will eventually reach an equilibrium charging state due to ion-particle interactions
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