The influence of ions on atmospheric particle growth - flow tube and aerosol chamber studies
Final Report Abstract
The atmospheric aerosol, among other things, plays an important role in the climate system and affects human health. Therefore, it is important to understand and quantify aerosol sources and sinks. One of the important sources of new particles in the atmosphere is so-called secondary aerosol formation, i.e. gas-toparticle-conversion as a result of chemical reactions of atmospheric precursor gases such as volatile organic compounds. Mechanisms of new particle formation including particle nucleation and/or condensational particle growth are widely studied. In this project, the influence of atmospheric ions on new particle formation and specifically the growth of particles by condensation of low-volatility vapors in the presence of ions were experimentally investigated. It was expected that ions facilitate new particle formation and that ions lead to faster growth of particles because vapors condense more easily onto electrically charged particles due to electrostatic attraction. A main objective of the project was to constrain the diameter range in which particle growth is influenced by ions. In a series of experiments, an impact of ions on the charging state of particle populations formed by oxidation of organic precursor gases (α-pinene and limonene) in a laminar flow tube was not observed for particle populations with a geometric mean diameter of 16 nm or larger. This result is in line with other studies in the literature. In atmospheric measurements, negative overcharging of particles, i.e. a larger fraction of negatively charged particles than expected in bipolar charge equilibrium, was observed at the beginning of precipitation events, as well as just before new particle formation events and during new particle formation events at the leading edge of the growing particle population. Also, in field measurements, slightly enhanced growth rates of particle populations in artificially ion-enriched air were observed, however, within the limits of measurement uncertainty. Laminar flow tube experiments indicated that particle number concentrations were enhanced in the diameter range below 10 nm in the presence of ions (by a factor of up to 2 – 3 at 5 nm diameter with a large measurement uncertainty). This corroborates the earlier finding that particle populations reach charge equilibrium in the early stages of particle growth. Additional laminar flow tube experiments coupled with a Neutral cluster and Air Ion Spectrometer (NAIS) led to unexpected particle growth events initiated by ions. Under steady-state flow tube conditions with constant concentrations of the organic precursor gas and ozone, new particle formation was not observed until ions were added to the flow. The fast growth of the ion-initiated particle population was analyzed and quantified using the NAIS data set. These results clearly indicate the potential of ions to facilitate new particle formation, in particular in the very early stages, and sets the basis for follow-up research to better understand the gas-toparticle conversion processes most strongly influenced by the presence of ions.
Publications
- (2017) Influence of reaction time and ozone concentration in flow tube studies of secondary organic aerosol formation from α-pinene ozonolysis. BayCEER Workshop 2017, University of Bayreuth, Germany
Serdarevic, N.L., Katkevica, S., Held, A.
- (2019) A case study of the impact of atmospheric ions on new particle formation events in the Fichtelgebirge mountains, Germany. European Aerosol Conference EAC 2019, Göteborg, Sweden
Held, A., Rumscheidt, D., Serdarevic, N.L.
- (2019) Flow reactor experiments to study the influence of ions on secondary aerosol formation. European Aerosol Conference EAC 2019, Göteborg, Sweden
Serdarevic, N.L., Held, A.
- (2019) Flow reactor experiments to study the influence of ions on secondary aerosol formation. UFP Symposium 2019, Berlin, Germany
Serdarevic, N.L., Held, A.
