10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Atmospheric Relevance of Laboratory Experiments on Ion Composition Based on Ion Composition Simulation
KALJU TAMME, Aare Luts, Urmas Hõrrak, Jaan Salm, Heikki Junninen, University of Tartu
Abstract Number: 207 Working Group: Aerosol Modeling
Abstract Composition of small atmospheric ions depends on trace gas composition and concentrations. Atmospheric ions are produced by ionization sources and evolve through a cascade of collisions between ions themselves and neutral trace gas molecules, and are absorbed by recombination, coagulation with particles and diffusion onto walls. Ionization is initialized by collisions of high energy particles from outer space or by radioactive decay. The main motivation for conducting simulations was to evaluate the effects of temperature, sulfuric acid concentration and absence or presence of CO2 in reaction on the chemical composition of ions. This study was aimed to give an insight into atmospheric applicability of laboratory experiments that are often conducted in N2 or synthetic air environment. Among others, those experiments conducted in CERN the Cosmics Leaving Outdoor Droplets (CLOUD) were absent of CO2. Results from CLOUD showed higher ion concentration and ion-induced nucleation than measured in Hyytiälä, SMEAR station, Finland (Wagner et al, 2015).
The ion-kinetic model introduced by authors was used. Model contained 522 ion-molecule reactions with 166 ion species and 127 neutral compounds. Both, the time variations of the concentrations and the steady state concentrations of individual ion species were calculated. Technically, the time variations were simulated as the time evolutions of individual ion species by way of ion-molecular reactions that started from the primary ions (in this study, 5% O− and 95% O2−). The neutral species were regarded as constants. This assumption was justified because (atmospheric) concentrations of these neutrals were many orders of magnitudes higher than those of ions. The steady state concentrations were computed by the model considering both, the time evolution of the individual ion species and the parameters, that determine the ionization and sink characteristics in a given environment. A more detailed description of the model and some examples where it was used can be found in (Luts and Parts, 2002; Parts and Luts, 2004; Luts and Salm, 1994; Luts, 1994).
We used our model to simulate experiments with absence and presence of CO2, with different temperatures and different concentrations of H2SO4. When compared simulations where the changing parameter was CO2, we found that in the presence of CO2 the NO3−concentration were still higher than in those made without CO2. Also in the simulations where CO2 was present the O3− had much lower concentration. As a conclusion we found that CO2 has an effect on steady-state concentrations of ions. On simulations where the changing parameter was H2SO4, we saw that when H2SO4 concentration was higher the NO3− concentrations were lower. Investigating the behavior of cluster ion composition from temperature, we found that on most simulations NO2− and NO3− had higher concentrations at higher temperature.
This work was supported by European Regional Development Fund, project MOBTT42 under Mobilitas Pluss programme, and by the Estonian Research Council Projects IUT20-11.
R. Wagner et al.: (2017) The role of ions in new particle formation in the CLOUD chamber; ATMOSPHERIC.CHEM.PHYS, 17, 15181—15197.
T.-E. Parts, and A. Luts: (2004) Observed and simulated effects of certain pollutants on small air ion spectraI: Positive ions; ATMOSPHERIC.ENVIRON, 38, 1283—1289.
A. Luts, and T.-E. Parts: (2002) Evolution of negative small air ions at two different temperatures; J.ATMOSPHERIC.SOL.-TERR.PHYS, 64, 763—774.
A. Luts, and J. Salm: (1994) Chemical composition of small atmospheric ions near the ground; J.GEOPHYS.RES, 99 (D5), 10781—10785.
A. Luts: (1994) Evolution of negative small ions at enhanced ionization; J.GEOPHYS.RES, 100 (D1), 1487—196.