The ion-ion recombination coefficient α: Comparison of temperature- and pressure-dependent parameterisations for the troposphere and lower stratosphere

Abstract

Abstract. Many different atmospheric, physical and chemical processes are affected by ions. An important sink for atmospheric ions is the reaction and mutual neutralisation of a positive and a negative ion, also called ion-ion recombination. While the value for the ion-ion recombination coefficient α is well known for standard conditions (namely 1.7 · 10–6 cm3 s–1), it needs to be calculated for deviating temperature and pressure conditions, especially for applications in higher altitudes of the atmosphere. In this work, we review the history of theories and parameterisations of the ion-ion recombination coefficient, focussing on the temperature and pressure dependencies and on the altitude range between 0 and 20 km. Starting from theories based on J. J. Thomson’s work, we describe important semi-empirical adjustments as well as field, model and laboratory data sets, followed by a short review of physical theories that take the microscopic processes during recombination into account, including a molecular dynamics approach. We present a comparison between all theories, parameterisations, field, model, and laboratory data sets to conclude on a favourable parameterisation. While many theories agree well with field data above approx. 10 km altitude, the nature of the recombination coefficient is still widely unknown between Earth’s surface and an altitude of 10 km. According to the current state of knowledge, it appears most reasonable to assume a constant value for the recombination coefficient for this region, while we recommend using a parameterisation for altitudes above 10 km. Overall, the parameterisation of Brasseur and Chatel (1983) shows the most convincing results. The need for future research, be it in the laboratory or by means of modelling, is identified.

Look Up: Probing the Vertical Profile of New Particle Formation and Growth in the Planetary Boundary Layer With Models and Observations

“…The inorganic nucleation scheme represents, both neutral and ion‐induced, binary (sulfuric acid‐water) and ternary (sulfuric acid‐ammonia‐water) nucleation, although the RH (H 2 O) dependence is not included in this scheme. For the ion‐mediated inorganic NPF schemes, we used an ion‐recombination coefficient of 8.0 cm −3 s −1 , which is representative of the lower troposphere (Franchin et al., 2015; Zauner‐Wieczorek et al., 2021). Output from the organic‐sulfuric acid and inorganic NPF schemes are recorded in addition to the total nucleation rate.…”

“…For the ion-mediated inorganic NPF schemes, we used an ion-recombination coefficient of 8.0 cm -3 s -1 , which is representative of the lower troposphere (Franchin et al, 2015;Zauner-Wieczorek et al, 2021). Output from the organic-sulfuric acid and inorganic NPF schemes are recorded in addition to the total nucleation rate.…”

The ion–ion recombination coefficient α: comparison of temperature- and pressure-dependent parameterisations for the troposphere and stratosphere

“…15 K, 1.827 × 10 −5 Pa s θ Critical angle to enter the trapping sphere λ Ion-ion mean free path, in m λ +,− Mean free path of the positive, negative ion, in m λ air Mean free path of air, in m λ ion Mean free path of one ion, in m λ Mean distance of the last collision of a particle with a gas molecule before striking the limiting sphere surface (after Fuchs), in m µ Ion mobility, in m2 V −1 s −1 µ +,−Ion mobility of the positive, negative ion, in m 2 V −1 s −1 µ 0 Ion mobility at standard temperature and pressure, in m 2 V −1 s −1 σ Electrical conductivity of the air, in S m −1Ratio of Coulomb and thermal energy at distance δ (limiting sphere surface) on the data repository Zenodo: https://doi.org/10.5281/zenodo.7044018(Zauner-Wieczorek et al, 2022).…”