Tracking potential sources of peak ozone concentrations in the upper troposphere over the Arabian Gulf region

Three-day HYSPLIT back trajectories indicate that ozone levels are typically about 17% lower in the 6-12 km range under wind flow conditions from the East than in cases when trajectories came from the Mediterranean. High pressure may lead to subsidence of ozone from the upper troposphere/lower stratosphere and eventually cause an increase of ozone mixing ratios by ∼18% above average between 6 and 7 km, i.e. slightly above subtropical subsidence layer. Under the impact of regional convective activity and associated lightning, ozone mixing ratios can increase by more than 35% averaged over the 9-12 km altitude range. In both cases maximum ozone in the mid to upper troposphere reached more than 100 ppbv.