Air plasma kinetics under the influence of sprites

Abstract

A full time-dependent kinetic study is presented for the main microscopic collisional and radiative processes underlying the optical flashes associated with an impulsive (τ = 5 µs) discharge in the form of a single sprite streamer passing through an air region of the mesosphere at three different altitudes (63, 68 and 78 km). The kinetic formalism developed includes the coupling of the rate equations of each of the different species considered (electrons, ions, atoms and molecules) with the Boltzmann transport equation so that, in this way, all the kinetics is self-consistent, although, in the present approach, the electrodynamics (no Poisson equation is considered) is not coupled. The chemical model set up for air plasmas includes more than 75 species and almost 500 reactions. In addition, a complete set of reactions (more than 110) has been considered to take into account the possible impact of including H2O (humid chemistry) in the generated air plasmas. This study also considers the vibrational kinetics of N2 and CO2 and explicitly evaluates the optical emissions associated with a number of excited states of N2, O2, O in the visible, CO2 in the infrared (IR) and ultraviolet (UV) emissions of sprite streamers due to the N2 Lyman–Birge–Hopfield (LBH) and the NO-γ band systems. All the calculations are conducted for midnight conditions in mid-latitude regions (+38°N) and 0° longitude, using as initial values for the neutral species those provided by the latest version of the Whole Atmosphere Community Climate Model (WACCM). According to our calculations, the impact of 4 ppm of H2O is only slightly visible in at 68 and 78 km while it strongly affects the behaviour of the anion at all the altitudes investigated. The local enhancement of NOx predicted by the present model varies with the altitude. At 68 km, the concentrations of NO and NO2 increase by about one order of magnitude while that of NO3 exhibits a remarkable growth of up to almost three orders of magnitude. The variation of the O3 density predicted by the model in the sprite streamer head is negligible in all the altitudes investigated. The analysis of the time dependence of the electron distribution function (EDF) in the sprite plasma during the pulse reveals that the EDF transient is quite fast, reaching its ‘steady’ values during the pulse in less than 100 ns (much shorter than streamer head lifetimes). In addition, the calculated EDF during the pulse and in the afterglow is far from being Maxwellian, especially for energetic electrons (with ε > 30 eV). Finally, the evaluation of the mid-latitude nighttime electrical conductivity of air plasmas under the influence of a single sprite event reveals an increase of up to four orders of magnitude (at 68 km) above its measured background level of at an altitude of ∼70 km. This sudden increase in the electrical conductivity lasts for 100 ms (at 68 km), being shorter (∼1 ms) and longer (1 s) at 63 km and 78 km, respectively. The total power delivered by the streamer head of a single sprite event has been...

Vibrational kinetics of air plasmas induced by sprites

“…The second most important production mechanism of NO is the charge transfer reaction NO − + O 2 → O 2 − + NO. The rest of kinetic mechanisms underlying the densities of O ( 3 P), N ( 4 S), NO, NO 2 and NO 3 shown in Figure 2c are the same as those described earlier [Gordillo-Vazquez, 2008]. Regarding the production of N 2 O, it should be said that, for times less than 5 ms, it is driven by O − + N 2 → N 2 O + e while for times beyond the pulse duration, that is, greater than 5 ms, the reaction N 2 (A 3 S u [31] Since at the beginning of the pulse we have a cold atmosphere, without vibrational or electronic excitation, the set of rate equations is solved by considering as initial conditions that, at the beginning, N 2 (X 1 S g + , v = 0) = N 2 , where N 2 represents the nitrogen proportion in the gas phase mixture [Pintassilgo et al, 2009].…”

“…[5] The approach used to model the kinetics of air plasmas induced by sprites in the Earth mesosphere is firmly based on the present understanding of the chemical activity of sprites and how this activity influences the surrounding atmosphere [Gordillo-Vazquez, 2008;Sentman et al, 2008;Kamaratos, 2009]. This model assumes that most of the chemical activity due to sprites begins in their brightest regions, that is, in their initial and very short living streamer heads.…”

“…[8] The model equations describing the non-equilibrium air plasma chemistry induced by sprites during the initial stage (streamer heads) and in the afterglow have already been introduced and described in detail in a previous work [Gordillo-Vazquez, 2008]. The numerical integrator chosen is an important point since its robustness is crucial for keeping the stiff stability [Gear, 1971] that generally appears when solving highly nonlinear set of equations as those describing the kinetics of sprite induced air plasmas once the concentrations of the fast chemical components in the discharge have decayed to negligible values.…”

“…[10] The transport of electrons and ions by diffusion has not been considered because their time scales are usually longer than those of the kinetic reactions controlling the concentrations of electrons and most of the ions and neutrals and, consequently, the densities of most of the species have decayed to negligible values before their transport by diffusion starts to be noticeable [Gordillo-Vazquez, 2008].…”

In-package nonthermal plasma degradation of pesticides on fresh produce

“…These results point to the fact that the nonthermal plasma source was a source of reactive oxygen species (ROS) and excited nitrogen species (RNS). The gas phase chemistry of nonthermal discharges in air is complex and may involve as many as 500 reactions and 75 species [30][31][32]. Furthermore, complexity is also added by the wide ranges of length and time scales of such plasmas [33].…”