Athenian photochemical smog: intercomparison of simulations (APSIS), background and objectives

Environmental Software 8 (1993) 3-8

Athenian photochemical smog: intercomparison of simulations (APSIS), background and objectives N.

Moussiopoulos

Laboratory of Heat Transfer and Environmental Engineering, Aristotle University Thessaloniki, GR-54006 Thessaloniki, Greece

ABSTRACT Athens is suffering under severe photochemical air pollution levels. The spatial variation of the photosmo8 characteristics in the Athens basin reveals that air pollution levels in Athens are largely affected by local wind circulation systems. A complete picture of wind field pattern and air pollutant dispersion in Athens can only be achieved with suitable mathematical models. In view of its complexity and its manifold peculiarities, the situation in Athens qualifies as a test case for prognostic mesoscale models and photochemical dispersion models. As the frame of model intercomparisons and of attempts to evaluate model simulation results, the APSIS project was initiated. With the participation of more than 30 scientific teams from four continents, this project is expected to contribute to the refinement of atmospheric environmental software. Key Words: Photochemical Smog, Sea Breeze, Air Pollution Abatement, Model Intercomparison

INTRODUCTION Population growth and industrialization resulted in a concentration of about 40% of the Greek population, 50% of the registered Greek cars and 50% of the Greek industrial activities in the Greater Athens Area (GAA). The associated high anthropogenlc emissions combined with the topographical and meteorological features of GAA resulted in high air pollution levels. The visual results of atmospheric pollution, b~ag called "Nephos" (a brown cloud over the city), made their appearance in the 70's. Alarmingly elevated pollutant concentrations already threaten public health and cause irreparable damage to invaluable ancient monuments t. Until recently, sulphur dioxide and 'smoke' (i.e., suspended particulates with a diameter less than 9. pro) were considered to be the most critical constituents of the Athenian smog. As far as sulphur dioxide is con-

cerned, in the period 1974- 1985 a constant reduction of pollution levels has been achieved with corrective interventions which focussed to limitations in the use of heavy oil, reductions of diesel fuel sulphur content and periodic controls of combustions. Although during the last years an increasing trend of sulphur dioxide concentrations was observed in Athens, the corresponding pollution levels remain relatively Iowa. On the contrary, the smoke pollution levels in Athens are still high, in spite of a noticeable decrease in the mean annual smoke concentrations achieved in the period 19841989 by a regular control of industrial furnaces. Mean smoke concentrations of the order of 150 tLg/ma underline the necessity of imposing additional measures for a further reduction of smoke emissionsa. From the above it is cleat that the antipollution strategy implemented in Athens before 1990 was in a large extent successful as far as sulphur dioxide and

Environmental Software 0266-9838/93/$06.00 © 1993 Elsevier Science Publishers Ltd

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N. Moussiopoulos

smoke are concerned. Unfortunately, these pollutants have since long ceased to be the main characteristic of the Athenian smog. At present it is generally realized that the Athenian smog is predominated by photochemical oxidants, that is chemical substances formed in the atmosphere under the influence of solar radiation, when nitrogen oxides and hydrocarbons (and in lesser extent carbon monoxide) are present -~. The concentration levels of the main photochemical oxidants, i.e. nitrogen dio:dde and ozone, increased by more than 10% annually in the period 1984-1989. It should be noted that the ozone concentration is frequently considered as an indicator for the intensity of photochemical smog. The immission situation in Athens is monitored by the Greek EnvironmenLal Protection Agency operating several automatic measuring stations in the GAA2. The highest ozone concentrations are measured in the northern periphery of Athens and especially at a semirural location close to the suburb Liosia (Fig. 1). The evolution of the monthly mean ozone concentration at Liosia is illustrated in Fig. 2 4. The series of data

150 p g / m 3

100

50

0

198~

1984

1985

1988

1987

1988

1989

1990

Fig. 2. Evolution of the monthly mean value of the ozone concentration at Lio$ia 4.

exhibits an average increase rate of approx. 15% p.a.. It is evident that since 1987 the monthly mean values exceed 110 ~g/m -~, i.e. the EC health protection threshold to be computed as a mean over eight hours ~. It should be noted that in 1988 the moving eight hour average of the ozone concentration at Liosia exceeded 110 ~g/m3 on 140 days. This elucidates the alarming proportions of the risks to human health associated with the photochemical air pollution in Athens. ATHENS

TOPOGRAPHY

AND METEOROLOGY

As shown in Fig. I, Athens is located in a basin of approximately 450 km2 and is surrounded by fairly high mountains at three sides and the sea to the fourth. Industrial activities take place both in the Athens basin and in the neighbouring Thriasion plain (cf. solid areas in Fig. 1). Air pollution episodes occur in Athens repeatedly during all seasons of the year. Most of these episodes are associated with the development of sea breeze6, although the situation is even worse in case of stagnant conditions (i.e., a critical balance between synoptic and mesoscale circulations). The driving force for the intense sea breeze circulation in Athens is the high insolation during sumtude isopleths are contoured at I00 m intervals. Resi-

mer days with anticyclonic weather conditions. The characteristics of the sea breeze in Athens are well

dential areas are stippled, industriaJ areas in the

known from previous observational work 6 z: Firstly, the

Athens basin and in the Thrinsion plain are solid. The asterisk denotes the location of the ground-based meas-

sea breeze tends to stratify the atmosphere above Athens thus trapping air po~utants at a relatively

,tin K station Liosia.

small height above ground. In addition, a recirculation

Fig. 1. Topography of the Greater Athens Area. Alti-

APSIS." background and objectives and accumulation of air pollutants takes place con-

a

sisting of pollutants transported by the nighttime land breeze onto the sea and carried back to the basin by the daytime sea breeze; this results in an abrupt in-

b

5

External Data

crease of the pollutant concentration levels in the Athens basin during the day. Apparently, in the case of chemically reacting pollutants (e.g. photochemical oxidant precursors) significant chpmical transformations may occur in the course of this recirculation. On the other hand, radiational cooling frequently leads to very strong nighttime inversions; apart from the associated high ground level pollutant concentrations, high stabi-

Invento~/ C

Data

Data I

,~ztemal Dew

lity causes that large amounts of photochemical oxidants produced the previous day may persist at some height above ground where they are separated from surface NO emissions s. The above experimental findings on the horizontal I

and vertical distribution of ozone over Athens confirm earlier suggestions for the effect of sea breeze on photochemical pollutant transport and distributiong. Hence, models for the sea breeze circulation and the associated transport of photochemical pollutants appear to be applicable and might be useful in efforts to improve the air quality in the Athens basin 7. However, as far as the reliability of model simulation results of air pollution in Athens is concerned, a recent experimental study of nighttime air pollutant transport in Athens demonstrates the need for simultaneous modelling of both the details of the flow field and the stratification 10. AIR POLLUTION ABATEMENT IN ATHENS tl The air pollution abatement strategies adopted in the past for the GAA were not successful because of shortcomings in the approach followed. Until the beginning of the 80's, the intervention to the Athenian air pollution system resembled to what might be defined as "level one" strategy, i.e. measuzes" solely based on educational guess (Fig. 3a). Since the early 80's gradually "level two" strategy has been adopted (Fig. 3b). This concept implies that measures are based on the results of technoeconomicai studies. In spite of its advan-

* In this paper the term 'measures' is used as a synonym of 'actions'.

,~iuioo

In.aloft'

~

Dam

AIr(~au~l Dill I Air OuIH~ Standards

d

~.ltl;r Illl

Data

II d

i

Dalala~

Emission Inventory

~

Data

Air Q.iltIT I Dill i

Fig. 3. Outline of air pollution abatement strategy concepts. (a) Level one strategy (b) Level two strategy (c) Level three strategy (d) Level four strategy tages with regard to the cost of the intervention, the "level two" strategy is ineffective, as it does not guarantee that the desired air quality is actually achieved. This inability is caused by the absence of any control mechanisms, i.e. the lack of dynamic elements in the strategy. Dynamic elements may be added to the air pollution abatement strategy in two steps leading to the "level three" and "level four" strategies, respectively.

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N. Moussiopoulos

The first step consists in checking the degree of realization of pollution abatement measures in terms of the resulting emission reductions; by other words, it

frame of the EUROTRAC subproject EUMACtS. This

implies a steady comparison of the actual emission

such an intercompafison include the extensive testing of mesoscale models, the determination of advantages

levels to those expected according to the optimized emission scenario (Fig. 3c). Only by this procedure the measures can be reformulated, in order that their effi-

activity aims at an intercomparison of model simulations of photosmog formation in Athens. Benefits from

ciency be improved and the means of their realization

and weaknesses of individual model concepts and, in an attempt to evaluate the model results, useful comparisons between models and observations.

be refined. Although the "level three" strategy is sufficient to meet certain emission standards, it is stin inappropriate with regard to the main target, i.e. the achievement of the desired air quality improvements.

one dealing with wind flow simulation (exercise A) and the other referring to pollutant transport simulation

For the latter, an additional step is required: The expected reduction in emission levels has to be transduced to the expected air quality improvement. By this approach, i.e. with the "level four" strategy (Fig. 3d), the effectiveness of air pollution abatement measures can be checked in terms of the resulting decrease in air pollution levels. Hence, scenarios can be devised to ensure that expected air pollution levels do not exceed given air quality standards. Apparently, a fundamental prerequisite for the "level four" strategy is the availability of mathematical models capable of reliably predicting air pollution levels in the area of interest for any emission scenario.

Since 1990, the Greek government is adopting "level four" strategy for the abatement of photochemical air pollution in Athens. As the core of this strategy, measures were taken to drastically reduce road traffic emissions12. The first results from the implementation of this strategy are promising. An assessment of the strategy based on estimates of its possible impact on road traffic emissions up to the year 2000 and predictions of the corresponding ozone levels can be found elsewherel~ t4.

OBJECTIVES OF APSIS In view of the above discussion, the situation in Athens qualifies as a test case for environmental software ts. Therefore, in October 1991 APSIS "+ was initiated in the

•" 'a~iq' is the Greek word for 'arch'.

Two different exercises were defined within APSIS,

(exercise B: Bl without and B2 with chemical transformations). Common input data were distributed to be used by all participants. In the case of exercise A, these data consist of the topography and the synoptic conditions valid during the period of interest (see below). Input data for exercise B include also the emissions inventory and three-dimensional fields of meteorological quantities from sample prognostic wind model results. Those participating at both exercises were invited to study pollutant transport assuming both the distributed and their own prognostic wind model results. As a suitable time period to be simulated within APSIS, the photochemical smog episode of May 25, 1990, was selected. The synoptic conditions illustrated in Fig. 4 reveal that during this day rather weak pressure gradients were prevailing over Greece, while warm advection occured aloft. During night, the wind direction was from WNW close to the surface and from NW aloft (Fig. 5a). At noon a flow from WSW was observed in the lowest atmospheric layers (Fig. 5b). An important constraint for mesoscale phenomena on the day selected was undoubtedly the strong temperature inversion extending up to 920 mb at night and not breaking-up during the day (Fig. 5). This inversion w u maintained due to the already mentioned warm advection at upper atmospheric layers and resulted in a shallow local circulation system in the Athens basin. In almost all monitoring stations very light winds were measured on this day 17. In general, the weather conditions in Athens on May 25, 1990 could be classified as stagnant. The mixing height hardly exceeded 100 m at night and 200 m in the afternoon hours.

APSIS: background and objectives

7 10 mls

a

a

b ,.+

lo

.,+0o/+o 10 mls

+ i

C

~-

+to

.POo,,1..°

b

Fig. 5. Vertical wind and temperature profiles at the Hellenicon airport of Athens for May 25, 1990. (a) oooo U.TC (b) 1200 U T C

Until the end of 1992, more than 30 scientific teams from four continents representing twelve countries ex-

Fig. 4. Synoptic maps for May 25, 1990. (a) 700 hPa level, 0000 UTC (b) 850 hPa level, 0000 UTC (c) Surface level, 1200 UTC

pressed their interest to participate at APSIS. A first APSIS Seminar was organized on the occasion of the 7th EUMAC Workshop held at Porto Carras, Greece, September 28 - October 2, 1992.

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N. Moussiopoulos

REFERENCES 1 Skoufikhiis, Th.N. Effects of primary and secondary air pollutants and acid depositions on (ancient and modern) buildings and monuments, Proc. of the Symposium 'Acid Deposition, A Challenge for Europe' (Ott, H. and Stang], H., eds), CEC, 193-226, 1983. 2 Ministry for the Environment, Physical Planning and Public Works The Atmospheric Pollution in the Athens Area, Technical Report, VoL 1-4, Athens, 1989 (in Greek). 3 Gilsten, H. Formation, transport and control of photochemicai smog, in The Handbook of Environmental Chemistry, Vol. 4A (Hutsinger, O., ed.), Springer, 53-105, 1986. 4 Ministry for the Environment, Physics] Planning and PubUc Works Measurements of the Atmospheric Pollution in the Athens Ares for the Year 1988, Athens, 1989 (in Greek). 5 CEC, Council Directive 92/72, OfSciai Journal of the European Communities, L 297, 1992. 6 Lalas, D.P., Asimakopouloz, D.N., Deliginrgi, D.G. and Helmis, C.G. Sea breese circulation and photochemical pollution in Athens, Greece, Atmos. Environ. 17, 1621-1632, 1983. 7 Laias, D.P., Tombrou-Tsella M., Petrakis, M., Asimako-pouloz, D.N. and Helmis, C. An experimental study of the horizontal and vertica~ distribution of ozone over Athens, Atmos. Environ. 21, 2681-2693, 1987. 8 Cvitas, T., Gilsten, H., Heinrich, G., Klasinc, L., Lalas, D.P. ana Petrakis, M. Characteristics of air pollution during the summer in Athens, Greece, Stanb - Reinhalt. Luft 45, 297-301, 1985.

9 Lyons, W.A. and Cole, H.S. Photochemical oxidant transport: Mesoscale lake breese and synoptic scale aspecte, J. Appl. Met. 18, 733-743, 1976. 10 Asimakopoulos, D., Deligiorgi, D., Dracopouloz, C., He]mis, C., Kokkori, K., Lala,, L;., Sikiotis, D. and Varotsos, C. An experimental study of nighttime air pollutant transport over complex terrain in Athens, Atmos. Environ. 28B, 69-71, 1992. 11 Moussiopoulos, N. Infrastructure for the evaluation of the effectiveness of pollution abatement measures, Bu/letin of

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the Hellenic Association of Consulting Firms "Ta Nea" 19, 36-39, 1991 (Re-published in the Bulletin of the Technical Chamber of Greece 1647, 50-58, 1991), in Greek. Ministry for the Environment, Physical Planning and Pubtic Works Proposal for the Abatement of the Athenian Smog, Athens, 1990. Monssiopoulos, N., Pattas, K. and Samaras, Z. Measures for reduction of road traffic emissions and consequences to ozone formation in Athens, in Traffic Induced Air Po]lutlon (Pischinger, 11., ed.), Mittei]ungsn des Institutes fuer Verbrennungskraftmaschinen und Tbermodynamik, 351-362, 1992. Moussiopoulos, N. The Athens Experience, Lecture Notes, Air Pollution 93 Conference, Monterrey, Mexico, 1993. Moussiopouloz, N. Air pollution levels in Athens: A test case for environmental software, in Computer Techniques in Environmental Studies IIl (Zannetti, P., ed.), Computational Mechanics Publications, Southampton, 3-20, 1990. EUROTRAC, Annual Report 1991, Part 5, 1992. Sakeliaridis G., private communication, 1992.