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Variability and long-term trends of tropospheric ozone: Comparison and interpretation of measurements of Caucasian and Central European mountain sites using a Lagrangian approach

English title Variability and long-term trends of tropospheric ozone: Comparison and interpretation of measurements of Caucasian and Central European mountain sites using a Lagrangian approach
Applicant Staehelin Johannes
Number 110831
Funding scheme SCOPES
Research institution Institut für Atmosphäre und Klima ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Climatology. Atmospherical Chemistry, Aeronomy
Start/End 01.10.2005 - 30.09.2008
Approved amount 68'980.00
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All Disciplines (2)

Discipline
Climatology. Atmospherical Chemistry, Aeronomy
Meteorology

Keywords (3)

Ozone; Atmosphere; Chemistry

Lay Summary (English)

Lead
Lay summary
In this project we will study variability and long-term trends of tropospheric ozone at high mountain sites in the Caucasus and in the Alps. Ozone is not only a key pollutant of photochemical air pollution but also a strong greenhouse gas and its changes have significantly contributed to the changes in radiative forcing and therefore to the anthropogenic climate changes. In our project we will study ozone measurements of two mountain sites of Causcasus (Kislovodsk (43.7oN, 42.7oE, 2070 asl., measurements available since 1989) and Terskol Observatory (43oN, 42oE, 3100 asl, available since 2003) and Switzerland (Jungfraujoch, 46.50N, 7.9oE, 3580m asl, available since the early 1990s).Neither the long term ozone increase at Jungfraujoch nor the remarkable decrease at Kislovodosk is well understood at the present time. Three dimensional 10 day backward trajectories arriving at the mountain sites will be calculated in order to determine the most important processes for tropospheric ozone trends in the two mountain sites. In addition other background measurements such as Mace Head (Western coast of Ireland), Arosa (2100 asl (Switzerland) and Zugspitze (Germany), high mountain sites of EMEP network might be included as additional stations in the analysis as well as other trace gas concentrations and meteorological information.Changes in anthropogenic ozone precursor emissions and changes in transport of ozone from the stratosphere into the troposphere and transport patterns changes are expected to be the most dominating factors explaining the observed long-term ozone trends.
The trajectories will be calculated using the trajectory tool LAGRANTO based on fields of the ERA-40 data which is a homogenized data set of meteorological analyses generated by the European Centre for Medium Range Weather Forecasts (ECMWF). The individual trajectories are first tested for homogeneity of the flow by calculating clusters of trajectories. In order to distinguish between different contributing factors the trajectories will be classified into the following groups:
Class A trajectories include those air parcels with stratospheric origin.For identification we will use an algorithm recently developed (andtested) at ETHZ which can distinguish between reversible and irreversible transport across the tropopause based on potential vorticity (PV) and a residence time criterion. The time after irreversible entrance in the troposphere and the evolution of PV will be further used to estimate the effect of mixing of stratospheric with tropospheric air.
Class B trajectories are those with recent contact of the air parcel with(polluted) planetary boundary layer air of Europe or Asia. For that purpose we will use boundary layer height (BLH) stored in ERA-40. In order to characterize the ozone formation we will store the time after contact with planetary boundary layer air and solar radiation.
Class C trajectories include those trajectories with contact with planetary boundary layer emissions of another continent which can describe the effect of intercontinental transport, derived in the same way as class B trajectories.
The ozone measurements at the receptor points of the individual trajectories will be subsequently compared with the time evolution of ozone in the lower-most stratosphere (class A) and the temporal evolution of the anthropogenic ozone precursor emissions over different continents.This will enable us to compare the different factors for the individual continents. This comparison is particularly important for the term of import of ozone from the stratosphere to the troposphere which is not adequately described by present numerical simulations. The results are also expected to elucidate why background ozone at European background sites have increased during the 1990s while European anthropogenic ozone precursors have substantially decreased.
Direct link to Lay Summary Last update: 21.02.2013

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