Comment on “NO x production in laboratory discharges simulating blue jets and red sprites” by Harold Peterson et al. J. de Urquijo 1 and F. J. Gordillo‐Vázquez 2 Received 23 July 2010; revised 20 September 2010; accepted 9 November 2010; published 17 December 2010. Citation: de Urquijo, J., and F. J. Gordillo‐Vázquez (2010), Comment on “NO x production in laboratory discharges simulating blue jets and red sprites” by Harold Peterson et al., J. Geophys. Res., 115, A12319, doi:10.1029/2010JA015966. [1] After a careful reading of the paper by Peterson et al. [2009], we have found a number of misinterpretations, both on the experimental technique used, and in the measured current through the spark gap, from which important conclusions are drawn regarding the production of NO x . In particular, we have found inaccuracies in the method to evaluate the energy dissipated in the discharge gap, with a rather unclear description. The authors introduce some correction factors to evaluate the NO x concentration even though these lack a sound, necessary explanation. In our view, the experimental technique deserves revision and serious improvement, since we regard this work as one of the very few attempts up to now to study and quantify in laboratory experiments the complex chemical phenomena related to TLEs and, in particular, with NO x production during sprite and blue jet events in the upper atmosphere. [2] The research activities on experiments and simulations leading to a better understanding of transient luminous events (TLE) like sprites and blue jets is an emerging field within the geophysical community. The work by Peterson et al. [2009] represents an attempt to correlate the energy dissipated in the discharge plasma of a spark gap with simultaneous measurements of NO x concentrations. This work has been commented on previously by Nijdam et al. [2010], different lines than those presented in this comment. We concur with most of the comments and criticisms made by Nijdam et al. [2010], regarding some conceptual errors and erroneous calculations in the paper of Peterson et al. [2009]. Here, we are concerned with some misunderstand- ings and errors of interpretation of the experimental techni- ques, and its consequences in the accurate derivation of the amount of NO x that is actually produced in the discharge spark gap. [3] Figure 4 of Peterson et al. [2009] describes the elec- trical setup. Capacitor C is charged via the series combi- nation of the 2 MW resistor plus the CVR (current viewing resistor), the value of which is not given in the text. Assuming that CVR  2MW (which is shown below), then the RC time constant for charging the capacitor is 0.3 s, which is congruent with the minimum reported charging time of 1 s, that is, between three and four time constants. [4] By the time the high‐voltage discharge switch is pressed, the spark gap becomes conducting and forms a series circuit with the inductance L (1.255 mH), the charging capacitor C (0.15 mF), the CVR (unknown value or, at least, not given in the paper), and the spark gap. Nothing is said about the plasma impedance in the spark gap. Let us call R m the value of the CVR, and assume that the discharge plasma is predominantly resistive, and designate this property by R SG . Thus, the total resistance (R t ) in the series circuit is R t ¼ R m þ R SG ð1Þ [5] The current in the RLC series circuit of Figure 4 is correctly expressed by equation (3) of Peterson et al. [2009], although the natural frequency of oscillation, w 0 , is wrongly typed, since w 0 =(LC) -1/2 . Notwithstanding that the discharge gap should be represented by an impedance with inductive, capacitive and resistive components, and that these are time dependent, we shall only consider the resistive part, since this is the most relevant during discharge development other than the initiation and extinction stages. [6] The fourth paragraph of section 2.1 of Peterson et al. [2009] is particularly confusing and unclear. We would like to raise the following comments. [7] 1. In equation (1) of Peterson et al. [2009], the magnitude E is defined only as the energy, without identi- fying it with any of the components of the electrical circuit. [8] 2. Equation (1) of Peterson et al. [2009] aims at describing an energy balance during the discharge regime, but it is incorrect. The correct energy balance equation reads as 1 2 CV 2 0 ¼ Z R m i 2 dt þ Z R SG i 2 dt þ 1 2 Li 2 þ 1 2C V 0 C þ Z idt   2 ð2Þ where i = i(t) is the time‐dependent current in the circuit, and V 0 is the charging voltage of the capacitor. The term on the left‐hand side of this equation is the energy stored in capacitor C prior to the discharge. The third and fourth terms on the right‐hand side of equation (2) correspond to the 1 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Mexico. 2 IAA‐CSIC, Granada, Spain. Copyright 2010 by the American Geophysical Union. 0148‐0227/10/2010JA015966 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, A12319, doi:10.1029/2010JA015966, 2010 A12319 1 of 3