Ozone pollution during stratosphere-troposphere exchange events over equatorial Africa

Abstract

Both natural factors such as thunderstorm events and anthropogenic activities contribute to very high ozone production. On the flight route from Johannesburg to Vienna enhanced ozone and relative humidity spikes were observed by MOZAIC (Measurements of Ozone by Airbus In service airCraft). MOZAIC recorded high resolution in-situ ozone and relative humidity at a flying altitude of 250-200 hPa at equatorial Africa. This area is one of the lightning hot spot regions of the world. We report introduction of enhanced ozone of stratospheric origin into the troposphere during two events and the resulting pollution. Vertical cross-section of potential vorticity over the region of interest showed high PV intrusion below the tropopause level. Both OLR (Outgoing longwave radiation) and vertical wind have indicated presence of strong convection. Cloud water content transport and high latent heat have confirmed the existence of thunderstorm activity coupled to PV intrusion. The two distinct events are characterized by very low ozone within the thunderstorm cloud and very high ozone of stratospheric origin outside the thunderstorm cloud. The events have produced ambient air pollution