Figure 4. Variation of NO_x yield per unit energy with spark gap (squares : Chameides et al. [1977], circle : Levine et al. [1981], triangle : Peyrous and Lapeyre [1982], = : this work, 400 mbar pressure, discharge energies 31 - 84 J, energy per unit length 4.2W10³ - 7.8W10³ J m^-1).