Assessment of atmospheric processes driving ozone variations in the subtropical North Atlantic free troposphere [Discussion paper]

Abstract

An analysis of the 22-yr ozone (O3) series (1988– 2009) at the subtropical high mountain Izaña station (IZO; 2373m a.s.l.), representative of free troposphere (FT) conditions, is presented. Diurnal and seasonal O3 variations as well as the O3 trend (0.19±0.05%yr−1 or 0.09 ppbvyr−1), are assessed. A climatology of O3 transport pathways using backward trajectories shows that higher O3 values are associated with air masses travelling above 4 km altitude from North America and North Atlantic Ocean, while low O3 is transported from the Saharan continental boundary layer (CBL).