Ozone, ultraviolet flux and temperature of the paleoatmosphere.

Of all tropospheric species, ozone (O3) comes closest to being naturally present at toxic levels. In addition, O3 controls the ultraviolet flux reaching the Earth's surface and affects the temperature of the surface and atmosphere. For these reasons, O3 was an important species of the paleoatmosphere. Surface and atmospheric levels of paleoatmospheric O3 were calculated using a detailed photochemical model, including the chemistry of the oxygen, nitrogen, and hydrogen species and the effects of vertical transport. Surface and tropospheric O3, as well as the total O3 column, were found to maximize for an atmospheric oxygen level of 10(-1) present atmospheric level (PAL). Coupled photochemica/radiative-convective calculations indicate that the radiative effects of O3 corresponding to an oxygen level of 10(-1) PAL resulted in a globally-averaged surface temperature increase of 4.5 K.