Ozone and carbon monoxide at the Ushuaia GAW-WMO global station

Abstract Five years (2010–2014) of hourly surface measurements of ozone (O 3 ) and carbon monoxide (CO) at the GAW-WMO station in Ushuaia (Argentina) were analysed and characterised. A meteorological study of the region was carried out using in situ observations and meteorological fields from the ECMWF (European Centre for Medium-Range Weather Forecast) global meteorological model. Atmospheric transport was investigated with the air mass trajectories computed with HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model using ERA-Interim meteorological fields. Airflows primarily arise from the W-SW (South Pacific Ocean) which are associated with an almost permanent low pressure system. Collected winds from the South (Antarctic Peninsula and Weddell Sea), polar easterlies, occur less frequently. The hourly averages of O 3 and CO were 20 ± 7 ppb and 71 ± 45 ppb, respectively, typical values in remote environments. A clear seasonal pattern was obtained for O 3 , with a monthly peak in winter of 25 ppb and minimum in summer of 12 ppb. Similar behaviour was found for CO, with 93 and 48 ppb maximum and minimum values, respectively. Both species show a weak daily cycle with an amplitude of 2–4 ppb for O 3 and 13–20 ppb for CO. Peaks in O 3 and CO in the cold season could be associated with low photochemical activity, fewer destructive processes and transport of these species from the South Pacific. O 3 vertical behaviour was analysed using 139 O 3 soundings at Ushuaia in the period studied. The seasonal patterns and levels of the O 3 profiles from the surface up to 5 km are similar to measurements on surface and thus it can be assumed that the O 3 measured on the surface could be representative of the low-mid troposphere. To investigate the spatial distribution of O 3 and CO in this region and the spatial representativeness of the Ushuaia measurements, daily observations from the AIRS (Atmospheric Infrared Sounder) instrument on board the AQUA satellite were used. The results obtained show that the O 3 levels in Ushuaia could be representative of a wide region in the Pacific South and that the CO levels are representative of a continental region around the observatory.