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In mountainous regions, the vertical exchange between the boundary layer
and the free troposphere is enhanced, leading to a stronger venting of
pollutants, such as NOx, into the free troposphere.
Since the efficiency of ozone production per molecule of NOx
is higher for low NOx concentrations (free troposphere)
than for high NOx concentrations (polluted boundary
layer), the increased vertical exchange in the Alpine area may enhance
the ozone formation, averaged over both the boundary layer and the free
troposphere. This motivates the fundamental question of VOTALP II:
Before an answer to this question can be tried, different processes have to be understood:
Local ozone production in Alpine valleys
For a valley intensively studied during VOTALP I, the effect of emission reductions shall be investigated using Eulerian and Lagrangian model simulations.
Climatology of ozone influx from the stratosphere
Stratospheric ozone regularly reaches the Alps during tropopause folding events. Some intrusions are being studied in VOTALP I, but a longer time period is needed for a climatological assessment. It is intended to develop a "stratospheric intrusion index" to identify stratospheric intrusions using only routinely available data.
New aspects of vertical exchange between boundary layer and free troposphere
During VOTALP I, the vertical exchange processes due to valley winds and slope winds in an Alpine valley were studied. The exchange above Alpine foothills is completely different from that in valleys, but might be of similar magnitude. Boundary layer tops are higher above hills than above valleys in between and therefore boundary layer air and free tropospheric air might coexist at the same altitude. Two measurement campaigns are devoted to study this effect.
Advection of urban plumes into the Alps
The chemistry and dynamics of urban plumes are reasonably well understood, but their interaction with topography is not well documented, although their impact on the Alpine region could be of importance for the ozone formation in Europe. A large existing data set of aircraft measurements and Eulerian model simulations will be used to study the advection of the urban plumes of Milano, Munich and Vienna.
The Alpine effect on the European ozone concentrations
An assessment of the effect of enhanced vertical pollutant transport on the European scale will be attempted using different model studies. Eulerian model simulations with treatment of chemical reactions will be used to understand and quantify the relevant processes. A half-year Lagrangian particle dispersion model simulation with particle releases in high-emission areas close to the Alps will be performed to study whether, how often and where pollutants transported into the free troposphere above the Alps are fumigated back into the boundary layer above Europe. Combining the results from this climatological approach that only accounts for the pollutant dynamics, but not for chemical reactions, with the results from the case studies with full treatment of chemical processes will give a tentative estimate of the effect of the Alps on European ozone concentrations.
The high resolution VOC emission inventory for the valley is checked by comparing model simulations and VOC measurements available from the campaign (FhG, FKKT). Having tested the reliability of the inventory further Eulerian model simulations are made on a grid of about 0.5 km horizontal resolution (FhG). The simulations deal with specific emission reduction scenarios. Special emphasis is given to traffic reduction scenarios for the motorway N13 which passes this valley along its main axis. Another scenario simulation is done to estimate the influence of biogenic VOC emissions on the local photooxidant production (photochemical ozone creation potentials) by switching off the biogenic sources of VOCs.
In VOTALP 1, the applicability of the Lagrangian box model concept in complex terrain is studied. A photochemical box model is combined with a boundary layer model developed especially for complex terrain. Three scales of the transport processes have to be considered, namely the transport towards the Alpine region, the transport across the foothills to the valley entrance and the transport within the valley. The model performs well for long-range simulations, is being evaluated for the valley entrance, but the concept might bring about problems within the valley. Therefore, different concepts have to be tested to overcome the problems. Using the experience gained in VOTALP I, a Lagrangian box model concept is developed, which remains valid as a reasonable approximation even within a valley (IMP). The box model is evaluated by comparing simulated ozone concentrations with measurements at the entrance of the Mesolcina Valley as well as within the valley or at the slopes for one summer season (IMP). Using the validated Lagrangian model, emission reduction scenarios are calculated for one summer, giving a climatological assessment of the impact of changing emissions during different weather patterns (IMP).
Different approaches to calculate such an index are tested for specific episodes. For this purpose, a Eulerian photochemical model version with high vertical resolution in the tropopause region and with detailed treatment of boundary layer chemistry and transport processes is set up (IGM-K). Calculations are done for two different episodes. If these simulations show that the index is a reliable indicator of stratospheric influence, it can be applied to assess the reliability of tropospheric and boundary layer chemistry models. Using this index, the seasonal variation and climatological importance of troposphere-stratosphere exchange in the Alpine region is investigated (IMP).
On at least two days aircraft measurements are done (MetAir) that follow north-south cross sections between the urban areas and the Alps. A high temporal resolution of 0.2 seconds is achieved for H2O, CO2, NO2, O3 and vertical wind measurements, allowing eddy correlation analyses. Ozonesoundings are done using a mobile sounding system instrumented with GPS (PSI). O3 and aerosol measurements with a ozone lidar/Doppler sodar system are provided (FhG) at different places between the source regions and the Alps to derive the ozone fluxes. Complementary trace gas (e.g., O3, NO2, SO2, CO, N2O) measurements are carried out with a mobile FTIR/DOAS system (FhG). For the Munich-plume data from the stationary lidar in Garmisch and the monitoring stations Garmisch/Wank/Zugspitze are provided as additional information (FhG). On-line measurements of meteorological parameters, O3, NO, NO2, J(NO2) and VOC are performed at two ground stations, one close to the urban area and one in the foothills (FKKT). Additional off-line VOC measurements are performed for better VOC characterisation (FKKT).
Using the results of the campaigns, a budget analysis is done (PSI, FhG, FKKT). Aircraft data are used to calculate vertical fluxes of water vapor, CO2, O3 and NO2. The horizontal advection of the measured species is calculated. The boundary layer budget is analysed by combining aircraft data with boundary layer heights derived from radiosoundings using a boundary layer model. The boundary layer top entrainment is calculated from the buoyancy flux (PSI). The entrainment is compared with the entrainment over the Po Valley and the Alpine region (Mesolcina Valley and surrounding).
Another interesting existing data set consists of the measurements at the Garmisch (740 m) - Wank (1780 m) - Zugspitze (2962 m) sites in Bavaria. For Zugspitze, the records comprise O3, CO, CO2, CH4 NO, NO2, 7Be and natural radioactivity. For Wank they comprise O3, CO2, NO, NO2, SO2 and CO (for a few months only). For Garmisch, O3, NO, NO2 and SO2 are available. This data set and the meteorological data are made available from 1990 onwards (FhG). A data analysis is done aiming at a detailed characterisation of the individual air masses (oceanic, subtropical, stratospheric, regional influence) reaching the measurement stations and a classification of the respective O3 concentrations with respect to background levels, advection of air masses with photochemically enhanced O3 levels or O3 loss due to pollution. The frequency of occurrence of the different air masses and the differences between the respective ozone and precursor concentrations is studied climatologically (FhG). This work is supplemented by analyses of back trajectories and classifications of general weather types (IMP). Especially, a climatological estimate of the contribution of Munich to Alpine pollutant concentrations is aimed at.
One interesting episode of pollutant advection towards the Alps from Milano or Munich is selected for detailed budget calculations. The modelling is done using a Eulerian modelling system based on the MM5 mesoscale meteorological model (IGM-K). The chain of processes occurring during the advection from the source area to the receptor region is studied in detail. This includes emissions, chemical transformation and horizontal and vertical transport of photooxidants. A passive tracer is advected to understand the transport. Emission scenarios are calculated to estimate the effects of abatement strategies for the source regions on the concentration levels in the Alpine region.
Using the knowledge from VOTALP, the importance of vertical transports in the Alps for the chemistry of the lower troposphere above Europe is estimated. A model experiment is done (IGM-K) during a period with strong vertical transports. A hypothetical scenario is calculated for which topographical effects are disregarded by flattening the model topography. A comparison of ozone concentrations for this scenario with concentrations for the base case indicates the topographical influence on the ozone formation. Regional differences are investigated as well as the overall effect.
To investigate the dynamics and climatology of air parcels heaved into the free troposphere above the Alps, a half-year Lagrangian model simulation with a continuous particle release in urban areas close to the Alps is done (IMP in close co-operation with IMP-subcontractor LMUM, see section 3). The vertical particle transports in the Alps is parameterized based on the results of VOTALP I+II. Their subsequent fate will be simulated using three-hourly meteorological fields of a numerical weather prediction model (ECMWF). This allows to investigate how frequently pollutant reservoir layers formed above the Alps are entrained into the boundary layer above Europe and thus influence surface concentrations. The areas most affected by this process are identified.
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Scenario calculations for an Alpine valley |
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Lagrangian modeling for Alpine valleys |
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Measurements at mountain tops |
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Stationary lidar measurements |
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Stratospheric intrusion index |
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Alpine foothills: Milano campaign |
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Alpine foothills: Munich campaign |
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Urban plumes: analysis of existing data |
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Urban plume modeling |
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Calculation of summertime ozone budgets |
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Effects of the mountains: Eulerian model experiment |
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Effects of the mountains: Lagrangian model simulation |
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VOTALP II database |
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VOTALP II synthesis |
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IMP | Coordinator | Institut fuer Meteorologie und Physik der Universitaet fuer Bodenkultur, Vienna, Austria |
IGM-K | Contractor | Institut fuer Geophysik und Meteorologie der Universitaet zu Koeln, Cologne, Germany |
FhG | Contractor | Fraunhofer-Institut fuer Atmosphaerische Umweltforschung, Garmisch-Partenkirchen, Germany |
PSI | Contractor | Paul Scherrer Institut, Villigen, Switzerland |
FKKT | Associated Contractor | Fakulteta za kemijo in kemijsko tehnologijo, Univerza v Ljubljani, Ljubljana, Slovenia |
CNR | Contractor | Istituto FISBAT - C.N.R., Bologna, Italy |
MetAir | Subcontractor of PSI | MetAir AG, Illnau, Switzerland |
LRU | Associated Contractor | Labor für Radio- und Umweltchemie, Universität Bern, Bern, Switzerland |
IMP contributes to the work packages I, II, IV and V. Tasks of IMP are the coordination of VOTALP II, modelling of ozone and precursors in Alpine valleys, acquisition of data from Sonnblick and Hohenpeissenberg, calculation of air mass trajectories including potential vorticity, development of a "stratospheric intrusion index", analysis of existing aircraft measurement data and data from Zugspitze, Wank and Garmisch, urban plume modelling using a Lagrangian photochemical model, particle model simulations of the long-range transport of pollutants and the management of the VOTALP II database. The basic concept of the Lagrangian particle model simulations will be set up in cooperation with subcontractor Ludwig-Maximilians University of Munich, Germany (LMUM).
IGM-K participates in the work packages II, IV and V. Tasks are the simulation of stratospheric intrusion episodes to check the stratospheric intrusion index, the simulation of an advection episode of an urban plume towards the Alps, the calculation of ozone budgets for different weather patterns and the set up of an Eulerian model experiment to assess the effect of the Alps on vertical pollutant fluxes. All simulations are done using the EURAD modelling system.
FhG contributes to all work packages of VOTALP II. Tasks are the scenario calculations for the Mesolcina Valley, the measurements at Zugspitze, Wank and Garmisch, the measurement campaigns in the Alpine foothills, a data analysis to investigate the urban plume of Munich and the calculation of emission reduction scenarios for the Milano area.
PSI contributes to all work packages. Tasks are the modelling of ozone and precursors in Alpine valleys, the acquisition of routine data from Jungfraujoch and Payerne, vertical and horizontal budget calculations using the data of the Alpine foothill campaigns and urban plume modelling using a Lagrangian photochemical model. PSI subcontractor MetAir is responsible for aircraft measurements during the Alpine foothill measurement campaigns and makes available existing aircraft measurement data from 1991 onwards.
FKKT participates in the work packages I, III and V. Tasks are the validation of the VOC emission inventory needed for the scenario calculations in the Mesolcina Valley and the set up of ground stations during the measurement campaigns in the Alpine foothills.
CNR participates in the work packages II and V. Tasks are measurements of O3 and CO, decay products of 222Radon, 7Be and 210Pb, UVA and UVB radiation at Mt. Cimone and single-case studies of stratospheric intrusions.
LRU contributes to work package II. Tasks are the measurements
of 7Be, Radon and aerosols at Jungfraujoch.
Contract deliverables:
After one year, a progress report will be provided, describing all activities done so far. At the end of the project, the VOTALP II final report will be supplied, covering detailed reports on the activities of every work package and a detailed synthesis of the results.
Technical deliverables:
Because of the relatively short duration of the project, all technical
deliverables will be supplied at the end of VOTALP. The following
technical deliverables can be expected:
Content of technical deliverable | Type |
Scenario calculations for an Alpine valley (Eulerian model, Lagrangian model) | model results |
Measured data from Alpine peak observatories | data set |
Lidar measurements Garmisch | data set |
Trajectory data calculated for observatories | data set |
Stratospheric intrusion index | method |
Measurement campaigns for Alpine foothills | data set |
Chemical and meteorological data from 3 Bavarian sites since 1990 | data set |
Existing aircraft measurements | data set |
Model studies - urban plumes | model results |
Model study - summertime ozone budgets | model results |
Model experiment - effect of the Alps on European ozone concentrations | model results |
Particle model simulation - effects of the Alps on European pollutant levels | model results |
VOTALP database | database |
All VOTALP II reports are public. The access to foreground information, especially measurement data and models, is restricted until one year after the ending date of VOTALP II. The publication of data and results during the project has been regulated in a consortium agreement.