Electron energy distribution functions and transport coefficients relevant for air plasmas in the troposphere: impact of humidity and gas temperature

Abstract

A Boltzmann and Monte Carlo analysis of the electron energy distribution function (EEDF) and transport coefficients for air plasmas is presented for the conditions of the Earth troposphere where some transient luminous events (TLEs) such as blue jets, blue starters and gigantic jets have been observed. According to recent model results (Minschwaner et al 2004 J. Climate 17 1272) supported by the halogen occultation experiment, the relative humidity of the atmospheric air between 0 and 15 km can change between 15% and 100% depending on the altitude investigated and the ground temperature. The latter results cover a region of latitudes between −25 • S and +25 • N, that is, the Earth tropical region where lightning and TLE activity is quite high. The calculations shown here suggest that the relative humidity has a clear impact on the behaviour of the EEDF and magnitude of the transport coefficients of air plasmas at ground (0 km) and room temperature conditions (293 K). At higher altitudes (11 and 15 km), the influence of the relative humidity is negligible when the values of the gas temperature are assumed to be the 'natural' ones corresponding to those altitudes, that is, ∼215 K (at 11 km) and ∼198 K (at 15 km). However, it is found that a small enhancement (of maximum 100 K) in the background gas temperature (that could be reasonably associated with the TLE activity) would lead to a remarkable impact of the relative humidity on the EEDF and transport coefficients of air plasmas under the conditions of blue jets, blue starters and gigantic jets at 11 and 15 km. The latter effects are visible for relatively low reduced electric fields (E/N 25 Td) that could be controlling the afterglow kinetics of the air plasmas generated by TLEs. However, for much higher fields such as, for instance, 400 Td (representative of the fields in the streamer coronas and lightning leaders), the impact of increasing the relative humidity and gas temperature is only slightly noticeable in the attachment coefficient that can exhibit an increase of up to one order of magnitude at 11 km and 15 km for temperatures of 313 K and 308 K, respectively. Finally, a brief analysis is carried out on the impact of the gas temperature on the diffusion coefficients of neutrals and ions. The present results show quite reasonable agreement with available measurements in dry and moist air.

Scanning drift tube measurements of electron transport parameters in different gases: argon, synthetic air, methane and deuterium

“…The present data cover a wider domain of the reduced electric field than any of the previous works. All data sets agree [40], Ryzko [41], Roznerski and Leja [42] and Lisovskiy and Yegorenkov [43], Gordillo-Vázquez and Donkó [46]. reasonably well.…”

Laser filament-induced aerosol formation

“…The new particle formation in synthetic air shows an exponential increase with the water concentration. This points to the important role water molecules play in the formation of clusters (Kurtén et al, 2007) and underlines the relevance of the water molecules for the formation of reactive species like OH radicals in the plasma, which have the ability to generate condensable species like inorganic acids or oxidized organic molecules (Henin et al, 2011;Fresnet et al, 2002). Without additional trace gases added, the typical particle diameters generated range between 5 and 20 nm.…”

“…The observed differences in particle mass and number are not yet fully understood but may be influenced by the different amounts of water vapour with the higher water concentration favouring the particle formation, e.g. by higher OH radical yields in the plasma (Fresnet et al, 2002;Gordillo-Vásquez and Donkó, 2009). Furthermore, if the newly formed particles consisted of mainly inorganic molecules like HNO 3 , their volume would triple and the diameter would double by water uptake when changing the relative humidity from 60 to 97 % (according to the Aerosol Inorganics Model (AIM) (Wexler and Clegg, 2002)).…”

“…Despite the scatter in the individual data points, the particle formation rate ranges from a few 10 6 cm −3 plasma s −1 for weak filamentation up to 5 × 10 9 cm −3 plasma s −1 for strong filamentation for water molecule concentrations between 8 × 10 16 and 3.2 × 10 17 cm −3 corresponding to relative humidities between 25 and 98 % at 283 K. The abundance of water vapour obviously plays an important role for the generation of reactive species, e.g. ions and radicals (Fresnet et al, 2002;Gordillo-Vásquez and Donkó, 2009) in the laser plasma, and therefore can strongly influence the particle formation rates. Experiments in humid argon and nitrogen show enhanced particle production rates as compared to humid air for similar water concentrations (cf.…”

Chemistry in glow discharges of H2/O2mixtures: diagnostics and modelling

“…The actual shape of the electron energy distribution function (eedf) is not known with precision in our plasmas. On the one hand, inelastic and reactive collisions can deplete the high energy tail of a thermal eedf [75][76][77]. On the other hand, a small amount of non-thermal electrons, with energies extending to that corresponding to the cathode-anode voltage, can also be present in the discharge [78][79][80].…”