Tropospheric ozone and its regional transport over Cape Town

As part of efforts to understand the sources of air pollution in Cape Town. this study investigates the local variation of tropospheric ozone (O-3) and identifies possible advection paths of O-3 pollution from a remote source to Cape Town. Measurements of O-3 and wind from three sites in the Cape Town area were analyzed to study the local variations of O-3. At each site, the diurnal variation of O-3 is found to be mainly driven by photochemical production while the seasonal variation of O-3 is mostly driven by wind conditions. The highest concentration of O-3 is observed at the remote site (Cape Point) while lowest O-3 concentration is observed at the sub-urban site (Goodwood), where there are chemical sinks of O-3 such as NOx. Atmospheric pollution over southern Africa was simulated to study the regional transport of O-3. The simulations show that extreme O-3 levels in Cape Town can be caused by air pollution transported from the industrial Highveld of South Africa, in the lower troposphere. Such extreme O-3 pollution events over Cape Town are simulated to occur in January (14%), March (44%), April (28%) and September (14%). Lagrangian trajectories suggest four paths by which air parcels can be transported from the industrial Highveld to Cape Town: a north-easterly path which is the most frequent route, a tropical deviation route, a deviation along the south coastline and an oceanic deviation path which is the less frequent route. The major advection paths associated with poor air quality in Cape Town are the north-easterly route and the path along the south coastline of the country. Hence the study suggests that emissions in the industrial Highveld may contribute to O-3 concentration in the Cape Town area. (C) 2014 Elsevier Ltd. All rights reserved.