Ozone pollution over the Arabian Gulf – role of meteorological conditions

Abstract. The Middle East and particularly the Arabian Gulf region are characterised by highly favourable conditions for O₃ formation in summer. We investigated the role of meteorological conditions in O₃ formation using the WRF-chem model. The dispersion of air pollutants strongly depends on local wind patterns, in particular the persistent low-level north-westerly flow known as the summer Shamal, and recurrent land-sea breeze circulation systems.

A general finding from our simulations is that extreme pollution events, with O₃ mixing ratios exceeding 150 nmol mol⁻¹, can occur regularly over the Arabian Gulf, however, their location and magnitude can vary widely. O₃ mixing ratios are highest when the outflow of the regions with major anthropogenic emissions along the coast is advected over the Gulf, where pollution plumes are captured in the shallow and stable marine boundary layer allowing little ventilation. The sea-breeze circulation often causes onshore advection of the pollution in the afternoon, affecting the densely populated coastal regions along the western shoreline of the Gulf.

When the pollution is transported deeper over land, O₃ mixing ratios are generally lower due to rapid dilution of precursor gases in the very deep convective boundary layer over the desert.