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AUT Progress Report

Aristotle University of Thessaloniki,
Laboratory of Heat Transfer and Environmental Engineering

Authors: Nicolas Moussiopoulos, Kostas Karatzas
Edited by: Kurt Fedra

Progress by Work Packages

WP01: Various tasks performed concerning the preparation of the new co-ordination status after the red flag procedure.

WP02: As part of the Dissemination and User Group activities, the ECOSIM project was presented during the 1st Int. SATURN Workshop (a subproject of EUROTRAC-2) in Thessaloniki, Greece, August 1997. Moreover an introduction to the ECOSIM project was made in the frame of a presentation concerning "Athens Air Quality", in Pollutec'97, Paris, October (Moussiopoulos et al., 1997c). The ECOSIM project was also presented during a workshop of the Greek "Human Network for Air Pollution Simulation-HYDRA" held in Athens, Greece, during April 1997.

WP03: A scenario meteorological design for pilot case studies for Athens was conducted (to serve as input to WP07). Clarification of scenario analysis and data provision problems has been accomplished.

WP04: Preparation for major and critical functional specifications and design details of the demonstrator in view of the April 97 - Athens Technical Meeting was made.

WP05: Individual testing of parts of the models were carried out. Sensitivity Analysis (in the sense of what if analysis, see Kleijen, 1996) concerning the integration of Sea Surface Temperature (SST) information from POM to MEMO was performed, showing that the Demonstrator would not benefit from this coupling (see Annex II). Scheduling and planning of cgi-script interfaces for MEMO/MUSE-Demonstrator are completed, construction is being finalized. Data-exchange specifications for MEMO/DYMOS coupling has been accomplished. Athens air quality monitoring data have been prepared. Integration of these data to the Demonstrator was performed by ESS. Interface of Berlin input data with MEMO/MUSE is being finalized.

WP06: Berlin runs with MEMO completed; post-processing of results needs to be done.

WP07: AUT has invested many years of expertise to the study of the air flow and dispersion in the Athens domain (Kunz R. and Moussiopoulos N., 1995; Moussiopoulos N., 1985; 1989; 1993; 1994; 1995; Moussiopoulos et. al., 1995; Moussiopoulos N. and Papagrigoriou S., 1997; Moussiopoulos et. al., 1997; 1997b). As a part of the validation process, AUT has conducted multiple MEMO test runs for the Athens case. In addition, SST from POM data were integrated to MEMO and its influence to the sea breeze circulation was studied for a typical sea breeze day (case 5, see Annex I). Because of the availability of model input data or the Athens case, an existing 72x72 km2 was used instead of the 100x100 km2 domain initially agreed upon and used by the coastal water quality model POM.

The 72 x72 km2 domain proved to be appropriate for the study of urban air pollution in Athens, even without using nesting techniques in model applications. This was in agreement with previous studies (Kallos et al, 1993; Kunz and Moussiopoulos, 1995; Moussiopoulos et al, 1997).

In the frame of the multiple model runs a typical sea breeze case and a worst case meteorology were fully investigated via MEMO/MUSE with regard to the formation of photochemical pollution. Results were presented in the Athens April 97 Technical meeting.

In the light of WP03, the selected Athens predefined meteorological scenarios were compiled. Moreover, the functionality of emission scenarios was finalized, and a joint decision was made (AUT, ESS, GMD) for adoption of emission multipliers for each emission source category. This approach has already proved to be efficient serving user needs and requirements (Kurruvilla et al., 1994) while being also simple, thus overcoming the known problem of complexity in scenario formulation (Novak et. al., 1995).

MEMO/MUSE runs were performed for all meteorological scenarios and for the base emission scenario case (based on 1990 data, see Toll et. al., 1995). In addition MEMO data were provided to GMD to serve as input meteorological data for DYMOS. More over as part of the validation procedure, a detailed comparison with observations was compiled for two of the meteorological scenarios, 25 May 1990 and 7 July 1994.

B. Problems

Problems occurred with orography and land use data for Athens which were not available in electronic form as required for implementation in the Demonstrator. Additionally, cost for digital geographic data for Athens of 25-30 kECU would arise, as most of these data could be made available with the cooperation of private enterprises, while only small fragments of these data are available through public organizations. In addition, emission data for Athens could not be provided by MEG and ENVECO, and were made available by AUT.

2. Personnel & Tasks

Reduced person-months spent than initially planned during the reporting period, due to a delay in project start and the red flag procedure.

3. ECOSIM Demonstrator

Athens has (until now) not installed a local Demonstrator due to the lack of appropriate computer hardware (workstation as specified in the ECOSIM hardware/software specifications.

There are still difficulties porting the Demonstrator from the SUN platform to the MEGs HP platform (no definite specifications available from MEG). As a result scenario analysis and supporting tasks on behalf of the end user (MEG) have been delayed. In addition, AUT can not proceed with any validation activity of the Demonstrator and therefore proceeded in validation activities for the "stand alone" model modules.

4. Delays

See issue 2

5. Administrative Matters

The red flag procedure caused increased expenses and delayed finance. In more detail, AUT had spent nearly all of its 50% advanced payment until April 1997, although less person months were "consumed" than scheduled in the Technical Annex for the project. This was the result of:

  • unforeseen costs (e.g. increased travel costs, amounting to nearly 14,000 ECU, mainly as a consequence of the red flag procedure) and
  • the fact that labor costs are subject to VAT in Greece, which had to be covered from project resources. AUT will apply for reimbursement of this amount by the Commission but the timing of the reimbursement process cannot be predicted.

As a consequence of the above, starting with mid April 1997, ECOSIM work was funded by a loan received from AUTs Research Committee, which however could not cover more than six weeks of payment for personnel.

Athens data collection

The focus point for the collection of air quality in Greece is a division of the ministry of the Environment, City Planning and Public Works (PERPA). PERPA is currently undergoing modernization of its environmental data banks through implementation of a workstation and PC network linked over the HELLASPAC network. The existing infrastructure provides access to a wide variety of data (SO2, NOx, ozone, CO and black smoke) through a monitoring network of 10 automatic measuring stations.

Validation and verification activities.

Although validation and verification of the modeling modules should take place after these modules are integrated into the Demonstrator, this was not the case here, due to the various delays reported. Therefore, these activities were initiated independently, with MEMO/MUSE as a stand alone air quality (modeling) module, and were based on the vast experience and previous model applications of AUT in the city of Athens (Kirchner et. al., 1997).

Two meteorological scenarios are investigated, case 1 and case 5 (compare the Validation Scenario definition for Athens), as the former represents a worst typical meteorological situation with stagnant conditions prevailing, while the latter represents a typical summer sea breeze case, according to the target study scenarios A1 and A2 for Athens.

High anthropogenic emissions in conjunction with the complex topographical and meteorological features of the Greater Athens area (GAA) result in alarmingly high air pollution levels. The visual result of atmospheric pollution, called "Nephos", made its appearance in the 70s. In the last decades, sulfur dioxide and smoke were considered to be the most critical constituents of the Athenian smog. Therefore, air pollution abatement strategies implemented in Athens before 1990 mainly focused on the above mentioned pollutants and have been, to a large extent, successful. However, these pollutants have long ceased to be the main characteristics of the Athenian smog. At present it is generally realized that the Athenian smog is predominated by photochemical oxidants (Mantis et al., 1992).

Short model description

The formation of photochemical smog in the GAA is studied with the multi-layer photochemical dispersion model MUSE, which is one of the core models of the EZM. The EZM system is a complete system for simulating the wind flow and pollutant transport and transformation in the mesoscale. Main modules of the EZM are the nonhydrostatic mesoscale model MEMO (Flassak, 1990), the photochemical dispersion model MARS (Moussiopoulos, 1989) and the multilayer dispersion model MUSE (Sahm et al., 1997) which was developed as a simplified version of the 3-D dispersion model MARS.

Case specification

As suitable time periods for the simulations with MUSE, the photochemical smog episode of 25 May 1990 (case 1, Annex I) and the meteorological situation of 7 July 1994 (case 5, Annex I), were selected. The conditions prevailing on 25 May 1990 can be considered as the worst possible regarding the potential for the occurrence of an air pollution episode in Athens. The second case, on the other hand, represents a "typical" day for the Attica peninsula. A detailed description of both cases may be found elsewhere (Moussiopoulos and Papagrigoriou, 1997).

Aspects related to the formation of photochemical oxidants were analyzed with the multilayer model MUSE in conjunction with the KOREM chemical reaction mechanism. The latter contains 20 reactive species in 39 reactions (Moussiopoulos, 1989). Several additional simulations were performed in the frame of a sensitivity analysis, the aim being to investigate both the influence of the chemical reaction mechanism on air quality predictions (by implementing the more complex EMEP and RACM chemical mechanisms instead of KOREM) and the response of the model to the use of the fully 3-D model MARS instead of MUSE.

The numerical grid used for all simulations corresponds to the standard 72 by 72 km2 APSIS domain (Moussiopoulos, 1993). Dots on the map denote the location of concentration field monitoring stations for which simulation results are presented (PIR = Piraeus, ATH = Athinas).

Five layers were considered in the vertical direction in MUSE, while 25 non-equidistant vertical layers are considered in MARS. In both cases the minimum spacing at ground level did not exceed 20 m. The necessary meteorological input was derived from results of the non-hydrostatic mesoscale model MEMO. Monthly average ozone concentration values for Athens have been used as initial and lateral boundary conditions at inflow. Though defined as boundary layer averages, these values have been used for all model layers.

The simulations for the 1990 emission scenario were based on the emission inventory characterized from a spatial and temporal resolution of 2 km and 1 h respectively. This inventory comprises all available estimates of the NOx, CO, SO2 and VOC emissions. The latter were allocated to selected groups of hydrocarbon compounds according to the source categories considered (Arvanitis et al., 1997b).

Results and discussion

Figure 2 shows the predicted near-ground concentration patterns of ozone (left) and NO2 (right) at 10:00 and 16:00 LST obtained for case 1. As clearly shown in the top left panel of Figure 2, during the morning hours ozone levels remain very low over the Athens basin, the main reason being the increased near-ground emissions which serve as fast-acting sinks for ozone. At the same time, high NOx emissions lead to a sharp rise of NO2 concentrations over the center of Athens as a consequence of the oxidation of NO (not shown here) to NO2. Higher ozone levels are formed only after NO is depleted. Consequently, the maximum ozone concentrations are reached in the afternoon; at 16:00 LST air masses rich in ozone reside primarily above the slopes surrounding the city of Athens. The same model results confirm that ozone levels remain low in the center of Athens even in the afternoon. It seems though that the city of Athens is entirely surrounded by areas where the ozone threshold value of 90 ppb (which corresponds to the population information threshold defined by the EU Council Directive 92/72/EEC) is exceeded.

Figure 2: Predicted surface concentration patterns of ozone (left) and NO2 (right) in the Greater Athens area for case 1. Contours are plotted from 50 to 180 ppb, every 10 ppb.

Figure 3: Predicted surface concentration patterns of ozone (left) and NO2 (right) in the Greater Athens area for case 5. Contours are plotted from 50 to 180 ppb, every 10 ppb.

Corresponding results regarding the ozone and NO2 concentration patterns for case 5 are presented in Figure 3. Specifically, Figure 3 shows the surface concentration patterns of ozone (left) and NO2 (right) at 16:00 LST obtained for case 5. The highest ozone concentrations are calculated for the regions north-west of the city of Athens, whereas in the center of the urban area ozone levels remain negligible primarily due to the aforementioned depletion reactions.

In Figures 4 and 5 model predictions for the diurnal variation of the surface level ozone and NO2 concentrations for case 1 are compared with available observations at the measuring stations of Piraeus and Athinas respectively (the location of these stations is indicated in Figure 1). Prior to any comment on the quality of the agreement between prediction and observation, it should be pointed out that differences between observed data and simulation results are not surprising in view of the fact that model results represent averages over the area surface of one grid cell, whereas the observed values are, at least to a certain extent, affected by the distance from the emission source as well as by local influences which can not be resolved by the model. Bearing the above in mind, MUSE results are generally in fair agreement with the observations, at least as far as the diurnal variation of the pollutants concentrations is concerned.

Similar results are obtained with the 3-D model MARS (left panels of Figures 4 and 5) which considers twenty non-equidistant layers in the vertical direction. The results also remain nearly unchanged by applying the more complex mechanisms EMEP and RACM instead of KOREM (right panels of Figures 4 and 5). The deviations between model results and observations as well as the variation of the simulation results by using different chemical mechanisms or models are more pronounced in the case of the Athinas station; yet, even in this case the agreement between predictions and measurements is still reasonably good.

The expected reduction of the threshold exceedance is shown in Figure 6. Comprising all ozone threshold exceedance, the so-called AOT90 values (acumulated exposure to ozone over threshold of 90 ppb) are obtained by summing up all ozone exceedances over the area and the period of simulation.

Figure 4: Predicted versus observed diurnal variations of the ground level ozone and NO2 concentrations at the station of Piraeus for case 1. The location of the station is indicated in Figure 1.

Figure 5: Predicted versus observed diurnal variation of the ground level ozone and NO2 concentrations at the station of Athinas for case 1. The location of the station is indicated in Figure 1.

Figure 6: Accumulated exposure to ozone over 90 ppb summed up for the whole model area for meteorological conditions as on case 1 and case 5 predicted with the EZM model.

Figure 7: Dependence of ozone production on NOx and VOC emissions (blue and orange areas respectively) predicted with the EZM model.

As in any other conurbation the implementation of ozone abatement strategies in the GAA basically relies on the reduction of NOx and VOC emissions. In order to distinguish between areas where the production of ozone mainly depends on the NOx concentrations (NOx limited areas) and areas where VOC concentrations are crucial (VOC limited areas) the indicator O3/NOz has been adopted, following a suggestion of Sillman (1995). Values of O3/NOz below 7 indicating VOC limitation are found mainly in the center of Athens whereas values above 7, which indicate NOx limitation, prevail over the surroundings of the city. As shown in Figure 7 the reduction of VOC concentrations over the city area and of NOx concentrations outside the city will lead to the largest ozone decrease.


The reasonably fair agreement between simulation results and observations for both cases considered suggests that the model MUSE is capable of adequately describing the situation in Athens and, therefore, can be used to attain reliable predictions for the emission scenarios.


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