A: ionization coefficient

B: attachment coefficient

d: inter-electrode distance

e: electron charge

E: electric field intensity

E₀: initial electric field intensity

E_br: breakdown field strength

F_br: braking force

f₀: propagation frequency

J: current density

k_B: Boltzmann constant

m_e: electron mass

n_i: number density of i^th component

n_e: electron density

N_g: background gas density

q_e: electron charge

Q_i: collision cross section of i^th component

r: electron position vector

r_s: streamer radius

t: time

T_fl: fire temperature

u_d: drift velocity

u_s: streamer velocity

Greek

α: ionization rate

β: attachment rate

δ: ionization potential factor

γ: electron affinity factor

σ: electrical conductivity

σ_i: imaginary component of σ

σ_r: real component of σ

φ_eff: effective collision frequency

ω = 2πf₀: angular frequency

Mathematical

d/dt: time derivative

$i=\sqrt{1}$ : imaginary