Air temperature and selected air pollutant variation during the partial solar eclipse of 11 August 1999, over the greater Attica area, Greece

Transcription

1 Air temperature and selected air pollutant variation during the partial solar eclipse of 11 August 1999, over the greater Attica area, Greece A. Mavrakis 1, S. Lykoudis 2 & G. Theoharatos 3 1 Environmental Physicist (MSc), Greece 2 Institute for Environmental Research & Sustainable Development, National Observatory of Athens, Greece 3 Laboratory of Meteorology, University of Athens, Greece Abstract The partial solar eclipse on 11 August 1999 as it evolved over Greece offered a unique opportunity to examine the behaviour of air temperature and the concentration levels of some primary pollutants under the observed reduction of solar irradiance as this was recorded in the greater Athens Metropolitan area. For this purpose we examine the variation of air temperature, SO 2, CO and NO concentrations, over the greater Attica area, during that day. The variation of solar irradiance affects the variation of air pollutant concentration in a variable way, while air temperature presents significant spatial and temporal variations. Even though one would expect that the reduction of solar irradiance should have a direct impact on the primary pollutants, this is not always so. It seems that a apart from land use distribution, altitude along with the distance from the seashore are also significant parameters affecting pollutant variations. Thus an initial grouping of the stations used might be possible, also allowing for a first assessment of the possible effect of the internal boundary layer on the observed distribution of air temperature and air pollution variations. Keywords: air temperature, air pollution, solar irradiance, solar eclipse. 1 Introduction The solar eclipse of August 11 th 1999 over Athens lasted from 11:41:27 to 14:34:3, peaking at 13:1:15, and with a total duration of 2:53:3. The

2 364 Air Pollution XII magnitude of the eclipse was rated as.822 regarding the solar diameter coverage fraction and.781 regarding the shadowed fraction of the solar surface. During the day of the eclipse the meteorological condition were ideal for observation: clear sky, calm winds and high air temperature. These conditions did not favour air pollution dispersion providing the opportunity to study the effects of the phenomenon on air pollutants. The temporal and spatial variation of air temperature and three primary pollutants, namely SO 2, CO and NO, is examined. The area of interest is the Attica peninsula, Greece, and more specifically the wider urban area of Athens along with the area of the Thriassion Plain, for which data suitable for the analysis in mind were available. 2 Data used The data used in this study is hourly values of air temperature, sulphur dioxide, carbon monoxide, and nitrogen monoxide from several stations located in the are of interest and operated by various authorities/institutes. Meteorological data were provided by the National Observatory of Athens (NOA, 2 stations) the Hellenic National Meteorological Service (HNMS, 1 station), the National Technical University of Athens [1] (NTUA, 1 station), the Bureau of Pollution Control and Environmental Quality of the Development Association of Thriassion Plain (GERPPE, 2 stations) and the Direction of Air Pollution and Noise Control of the Ministry of the Environment (PERPA, 1 station). Air quality data were provided by GERPPE (2 stations) and PERPA (1 stations). Some geographical characteristics of the stations used, are presented in Table 1. Table 1: Geographical characteristics of the stations used. Distance from Altitude Name (Abbreviation) Operator Type seashore (m) (m) 1 3 Pireas (PI) PERPA AQ* 1 2 Elefsis (EL) GERPPE AQ+Meteo 2 3 Elefsis Airport (AIR) HNMS Meteo 2 4 Aspropyrgos (AS) GERPPE AQ+Meteo 25 5 Nea Smyrni (NS) PERPA AQ 35 4 Geoponiki (GE) PERPA AQ Thission (NOA) NOA Meteo 4 8 Athinas (AT) PERPA AQ 5 8 Patision (PA) PERPA AQ+Meteo 5 8 Aristotelous (AR) PERPA AQ 5 2 Peristeri (PE) PERPA AQ Zografou (NTUA) NTUA Meteo 1 21 Ano Liosia (AL) PERPA AQ Marousi (MA) PERPA AQ Palaia Pendeli (PEN) NOA Meteo 15 4 Lykovrisi (LY) PERPA AQ *AQ: air quality

3 Air Pollution XII 365 The station of Thission is located on top of a small hill in the middle of Athens, covered with trees, while that of Palaia Pendeli is at distance of about 2 km from the city centre on a hill at the South-eastern part of Pendeli mountain. NTUA station lies on the western foothills of Hymettous mountain near on the eastern edge of Athens urban area, and is surrounded by open area covered by shrubs. The stations of Elefsis and Aspropyrgos are located to the west of Athens in a flat area (Thriassion Plain) with intense industrial activities while the station at the Elefsis Airport is located in a typical airfield open area. Patision, Athinas and Aristotelous stations are in the middle of densely populated and highly commercial areas near the centre of Athens. The station Geoponiki is also in the middle of Athens but it is surrounded by small industrial units. Peristeri station is located to the western part of Athens, in a densely populated area with many small industries. Nea Smyrni, Marousi and Lykovrisi stations are located in residential areas, the former on the south-eastern part of Athens and the other two on the north and north-western part. Ano Liosia station is located in a northwestern residential/ semi-urban area while Pireas lies in densely populated and commercial area very close to the sea. 2.1 Air temperature The drop of temperature during an eclipse is a clearly defined phenomenon, but it is influenced by many factors such as surface type or time of day. Over land, the drop of temperature is affected by latitude, with a minimum temperature decrease in high latitudes and a maximum near the equator Temperature [ O C] AS EL AIR PEN NOA PA NTUA SOLAR Solar Irradiance [W/m2] : 9: 12: 15: 18: Figure 1: Diurnal variation of solar radiation at NOA, and air temperature at all stations for August 11 th, The amount of drops varies with site, generally 1 o C over open ocean, 2 o C on a small tropical island, and approximately 3-4 o C over large areas. Recovery to normal values occurs at the end of the eclipse over the ocean and on small islands, but is delayed up to two and a half hours in continental situations. The temperature normally begins to drop 2 minutes after first contact, with a

4 366 Air Pollution XII minimum 2-2 minutes after maximum eclipse phase (MEP). The temperature variation in the troposphere is mainly confined to a very shallow layer up to 4 meters above the earth s surface. At hill stations, the drop is usually less than at lower levels, but comparisons are not always consistent [2, 3, 4, 5, 6, 7]. Figure 1 indicates that even though air temperature is dropping significant non-uniformity is observed across the area of interest, in terms of magnitude, time of occurrence as well as duration. For this reason we also examined the hourly temperature difference, DT. This could serve as an indication of the possible role of internal boundary layer in the variation of temperature response at the various stations [8, 9]. Two are the main factors that affect air temperature owing to the reduction of solar irradiance: a) the distance of the site from the seashore and b) the altitude of the site. 4. DT [oc] AS EL PA NOA PEN AIR NTUA : 12: 16: : 14: 15: Figure 2: DT, between 11: and Figure 3: Spatial distribution of DT for 16:. 13:. Figure 4: Spatial distribution of DT for 14:. Figure 5: Spatial distribution of DT for 15:. The effect of distance from the seashore is quite clear when we observe the temperature variation for the stations Elefsis, Aspropyrgos and Elefsis Airport.

5 Air Pollution XII 367 Air temperature drop commences with a delay of some 3 minutes at Elefsis and almost 9 minutes at the two inland stations, reaching its maximum 2 hours after MEP in all stations. Temperature drop in Elefsis reaches 4, o C, while in Aspropyrgos it is only 1,5 o C. At the Elefsis Airport station air temperature follows a course similar to that of Aspropyrgos. After the eclipse has ended air temperature did not return to its normal levels. In Elefsis there the temperature remained 1 o C below normal, while in Aspropyrgos it rose 2 o C above normal levels [1]. In the main Athens area all stations, with the exception on Thission, follow similar patterns with the temperature drop onset located about 9 minutes after the beginning of the eclipse, nearly in phase with MEP, and the maximum drop occurring 2 hours later. Thission presents an early response to the eclipse similar to that of Elefsis, with the temperature starting to drop even though not sharply - as soon as the phenomenon started (Figure 1) SO2 [µgr/m3] SO2 [µgr/m3] Figure 6: SO 2 diurnal variation, Pireas. Figure 7: SO 2 diurnal variation, Patision SO2 [µgr/m3] DSO2 [µgr/m3] 11: 12: 13: 14: 15: 16: AR AT PI GE MA NS AS EL PE Figure 8: SO 2 diurnal variation, Geoponiki. Figure 9: DSO 2 between 11: and 16:.

6 368 Air Pollution XII From Figures 2, 3, 4 and 5 it is evident that altitude has a direct effect on air temperature sensitivity to solar irradiance. All stations located at certain altitude protruding from the surrounding area exhibit a higher sensitivity indicated by the their earlier response to the solar irradiance change. So, Thission, Zografou and Palaia Pendeli stations show a decrease in DT since 12: almost in phase with the beginning of the eclipse, and the maximum drop around 14:3 half an hour earlier than the rest of the stations. The magnitude of the temperature drop follows the altitude being higher at Pendeli (3,5 o C) than in Zografou (2, o C) and Thissio (1,8 o C) CO [mgr/m3] CO [mgr/m3] Figure 1: CO diurnal variation, Pireas. Figure 11: CO diurnal variation, Patision CO [mgr/m3] DCO [mgr/m3] 11: 12: 13: 14: 15: 16: AT GE NS LY PI MA PE PA Figure 12: CO diurnal variation, Lykovrisi. Figure 13: DCO, between 11: and 16:. 2.2 Sulphur dioxide (SO 2 ) Sulphur dioxide concentrations reacted positively to the reduction of solar radiation as can be seen in Figures 6, 7 and 8 present the effect of the eclipse on the diurnal variation of SO 2 for three stations across the Athens area. The same is also evident from Figure 9 especially for Pireas, Peristeri and Geoponiki stations,

7 Air Pollution XII 369 where the hourly sulphur dioxide concentration difference, DSO 2, has positive values during the MEP. In Pireas DSO 2 presents a sharp drop just after MEP and then it is stabilised. Pireas station also presents the largest DSO 2 variation. A similar variation is observed for Aristotelous and Athinas but with greatly reduced absolute DSO 2 values during MEP. The rest of the stations present weaker DSO 2 variation NO [µgr/m3] NO [µgr/m3] Figure 14: NO diurnal variation, Pireas. Figure 15: NO diurnal variation, Patision. 15 NO [µgr/m3] : AT PI NS AS EL PE 12 2 LY PA AL : 12: : : : Figure 16: NO diurnal variation, Ano Liosia. Figure 17: DNO, between 11: and 16:. 2.3 Carbon monoxide (CO) Figures 1, 11 and 12 presenting the diurnal variation of CO for three stations across the Athens area, indicate that CO behaves similarly to SO 2, when the irradiance in reduced, that is positively, but in a much weaker way. In Pireas and Geoponiki we observed a direct response of DCO, calculated in a way similar to that of DT, with positive values during MEP and a more or less stable recession afterwards (Figure 13). Peristeri and Lykovrisi, residential areas at significant altitudes, as well as Patision present positive DCO values one hour later, at

8 37 Air Pollution XII 14:. During MEP Lykovrisi station had the largest DCO decrease and then a very significant increase and overall the largest variation of all stations. Finally Nea Smyrni presents positive DCO values at 15:. The rest of the stations present little or no DCO variation. 2.4 Nitrogen monoxide (NO) Nitrogen monoxide presented a behaviour similar to that of CO as can be seen from the diurnal variation graphs (Figures 14, 15 and 16). In Pireas DNO presented a steep rise, corresponding to a limited rise in absolute values, in phase with MEP. It is characteristic that the very next hour there is a steep decrease and then DNO gets stabilised. Pireas is the station with the largest DNO variation in absolute values (Figure 17). One hour later Lykovrisi presents positive DNO values remaining stable afterwards. Patision and Peristeri, even though on an upward trend since 12: attain positive DNO values only 2 hours after MEP, followed by a decrease. The rest of the stations present little or no DNO variation with alternating negative and positive values around zero. 3 Conclusions Air temperature drop exhibits significant temporal and spatial variation, regarding the time of occurrence, their magnitude, and the respective change rate. Stations seem to react similarly according to their common geographical characteristics. Thus, in terms of air temperature, the meteorological stations of Thissio, Pendeli and Zografou standing higher than their surroundings seem to react in phase with MEP. The next station to react is Elefsis lying close to the sea, followed by Elefsis airport and lastly the remaining two stations. Primary air pollutants do not respond in a dramatic way even though the do present a positive response to the sharp solar radiation reduction during daytime. In terms of air pollution stations seem to react to the eclipse primary in the order they are encountered moving inland from the seashore, but also according to their altitude- higher stations seem to react first, the later effect being less strong though. Despite the relative scarcity of the data, as far as solar eclipses are rather rare events and the meteorological conditions are not always favourable for analyses of the kind proposed herein, we might suggest that the temporal evolution and spatial distribution of the hourly differences of air temperature and the selected primary pollutants concentrations could be linked to the formation and evolution of the internal boundary layer, that is known to depend on the underlying land use, on the distance from the seashore and on altitude above sea level [8, 9].

9 Air Pollution XII 371 References [1] National Technical University of Athens, [2] Mariolopoulos, E.G., Observations de l Eclipse Totale de Soleil Memoires de l Observatoire National d Athenes,, Serie I.Astronomie, 1, pp , [3] Anderson R.C., Keefer D.R., Meyers O.E., Atmospheric Pressure and Temperature Changes During the 7 March 197 Solar Eclipses. Journal of the Atmospheric Sciences, 29, pp , 1972 [4] Anderson RC, Keefer DR, Observations of the temperature and pressure changes during the 3 June 1973 solar eclipse, Journal of the Atmospheric Sciences, 32,.pp , 1975 [5] Anderson J, Meteorological changes during a solar eclipse. Weather, 54, pp , [6] Mariolopoulos, E., Zerefos, C., Bloutsos, A., Repapis, C., Ozone and Temperature Balloon Measurements during the Annular Solar Eclipse of 29 April Proceedings. of the Academy of Athens, 51, pp , 1977 [7] Nastos P.Th., Philandras C.M., Kandilis Ph.I., Variation of Meteorological Parameters during the Solar Eclipse of 11 August 1999 at the Wide Area of Athens. Proc. 5th National Conference on Meteorology, Climatology and Atmospheric Physics, pp , 2. [8] Stull B.R., An Introduction to Boundary Layer Meteorology. Kluwer Academic, [9] Mousiopoulos N., Transport phenomena in the atmosphere, Gaichoudis- Gaipoulis, Thessaloniki, [1] Mavrakis A., Theoharatos G., Christides A., Asimakopoulos D., Variation of meteorological parameters and air pollutants concentrations over the Thriassion Plain during the solar eclipse of 11th August 1999, Proc. 5th National Conference on Meteorology, Climatology and Atmospheric Physics, pp , 2.