Meteoric smoke and H2SO4 aerosols in the upper stratosphere and mesosphere

Meteoric smoke has traditionally been understood as a passive tracer which follows the global mesospheric circulation. Smoke extinction measured by the Solar Occultation For Ice Experiment, however, shows that while this is true in the middle to upper mesosphere (pressure <similar to 0.2hPa), it is not true near the stratopause. Here the expected winter increase begins 3months earlier than in models. We suggest that the autumn extinction increase is due to H2SO4 condensing above the nominal stratospheric aerosol layer (similar to 5hPa). This is possible due to lowering of the H2SO4 saturation vapor pressure when the acid is neutralized through combination with meteoric metals. The appearance of neutralized H2SO4 aerosol in autumn is associated with the seasonal decrease in temperature. The combination of meteoric smoke and neutralized H2SO4 aerosols explains the observations and supports previous suggestions that H2SO4 could condense above the nominal stratospheric sulfate layer.