On the contribution of lightning to ultrafine aerosol formation

We propose that locally high concentrations of new ultrafine aerosols may b e generated within lightning channels, in which the air is initially highly ionized by discharge currents. In the channel, temperatures are sufficient ly elevated to ensure that preexisting condensed materials are vaporized, g enerating aerosol precursors at concentrations much higher than would be fo und in ambient air. As the channel expands and cools, ions that survive neu tralization attract condensable vapors and grow rapidly. Detailed microphys ical simulations indicate that ultrafine particles (>3 nm in diameter) may achieve concentrations of 10(5)-10(6)/cm(3) in the channel within 10 second s after a flash, leading to an effective "production index" of 10(13)- 10(1 4) particles per meter of channel. While lightning may generate very high l ocal concentrations of ultrafine particles, and occur worldwide, the overal l contribution to global aerosol production is estimated to be small.