Lightning: Estimates of the rates of energy dissipation and nitrogen fixation

The global rate of production of atmospheric NO is given by the product of the lightning energy dissipation rate and the NO yield per joule of discharge. A value for the global average energy dissipation rate is derived from the energy per flash and the global average flash rate; the latter is determined from satellite observations. The energy per flash determined from the optical measurements is in excellent agreement with that determined from measurements of electrical field changes; both give 4 × 10 8 J per flash. For a global flash rate of 100 s −1 , the global average energy dissipation rate is estimated to be 4 × 10 10 W; however, the uncertainty in this parameter is approximately a factor of 3. The NO yield is estimated to be (9 ± 2) × 10 16 molecules/J, a value in good agreement with numerous other theoretically and experimentally derived yields. The production of NO from lightning is thus estimated to be 2.6 × 10 9 kg N yr −1 with a range caused by uncertainties of (0.8–8) × 10 9 kg N yr −1 . Although lightning is a small source of fixed nitrogen to the biosphere, it appears to represent a major source of atmospheric NO to the remote troposphere.