Aircraft observations of trace gas correlations during MINOS 2001 - case studies on the origin of air masses

Jörg Heland1, Helmut Ziereis1, Hans Schlager1, Christine Hauser1, Paul Stock1, Anke Roiger1, Marian de Reus2, Michael Traub2 and Geert-Jan Roelofs3

1 Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
2 Max-Planck-Institute for Chemistry, PO Box 3060, 55020 Mainz, Germany
3 Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University,The Netherlands


During the MINOS campaign in August 2001 in situ measurements of a comprehensive number of trace gases were made during 14 flights with the DLR Falcon aircraft from Heraklion, Crete. The aim of the campaign was to characterize the air masses and to quantify the main chemical and dynamical processes involved in the Mediterranean area, such as the transport of air masses into and out of this region.
In this study trace gas correlations between O3 and NOy, O3 and CO, CO and NOy, and NOx and NOy have been calculated as altitude profiles and along the single flight tracks. Air masses of stratospheric origin are identified by high dO3/dNOy ratios together with a negative slope of O3/CO. Positive high correlations between CO and NOy in tropospheric air indicate the influence of anthropogenic combustion and/or biomass/forest fires. The slope of the NOx to NOy ratio can be used to distinguish between fresh and aged emissions. Together with trajectory data (MPI-Mainz) and results from ECHAM4 model simulations (University Utrecht), these correlations help to get a clear picture of the air masses sampled during the MINOS 2001 campaign. E.g. one of the main features observed during most of the MINOS flights was the relatively ozone-rich mid-tropospheric layer of stratospheric origin (dO3/dNOy>100, dO3/dCO<0, dCO/dNOy<0). In addition, polluted air masses in the upper troposphere (dO3/dNOy<100, dO3/dCO>0, dCO/dNOy>0) were observed during some episodes identified by the models as boundary layer air originating from India. During some flights a very sharp layering was found below altitudes of approximately 6 km in the lower troposphere and the planetary boundary layer with photochemically aged air and fresh emissions, mainly originating from Eastern and Central Europe.