PROMENE POTENCIJALA SOLARNE ENERGIJE USLED DELOVANJA ANTROPOGENIH AEROSOLA U ATMOSFERI TIRANE

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1 PROMENE POTENCIJALA SOLARNE ENERGIJE USLED DELOVANJA ANTROPOGENIH AEROSOLA U ATMOSFERI TIRANE MODIFICATION OF SOLAR ENERGY POTENTIAL DUE TO ANTHROPOGENIC AEROSOLS IN ATMOSPHERE OF TIRANA Urim BUZRA 1,a), Pellumb BERBERI 1, Driada MITRUSHI 1,Valbona MUDA 1, Daniela HALILI 2, Irma BERDUFI 3, Eduart SERDARI 4 1 Department of Engineering Physics, FIMIF, PUT, Tirana, Albania 2 Department of physics, FNS, AXHU,Elbasan, Albania 3 Institute of Nuclear Physics, INP, TU, Tirana, Albania 4 Faculty of technical Science, University of Vlora a) Corresponding author: rimibuzra@yahoo.com Promena svojstava iradijacije atmosfere tokom vedrih dana jeste, između ostalog, pokazatelj postojanja atmosferskih aerosola, i može se koristiti kao pokazatelj za procenu zagađenja vazduha i lokalnih promena potencijala solarne energije. Glavni cilj ove studije jeste procena uticaja antropogenih aerosola na solarnu energiju koja pada na horizontalnu površinu tokom vedrog dana u gradu Tirani. Analizirali smo i kvantifikovali uticaj aerosola na smanjenje količine solarne energije koja pada na horizontalnu površinu na zemlji u uslovima vedrog neba, uz procenu vremenske evolucije, na dnevnoj i časovnoj skali, takođe uzimajući u obzir nepovoljne efekte koje izazivaju relativna vlažnost, brzine vazduha i geometrijski faktor. Da bismo odredili prisustvo aerosola u atmosferi, složili smo se da koristimo umanjenje sunčevog zračenja nakon poslednjeg kišnog dana. Na sunčevo zračenje na horizontalnoj površini uticali su neki parametri: relativna vlažnost, aerosoli i geometrijski faktori. Svi podaci su korigovani po faktorima, kao što su promene relativne vlažnosti, brzine vetra i geometrijskih faktora, kao što su nagib površine i dnevna promena upadnog ugla sunčevog zračenja. Proučavali smo promen insolacije na tri lokacije sa različitim intenzitetom saobraćaja, jednoj lokaciji u gradu Skadru, i dve lokacije u gradu Tirani. Petnaest dana nakon poslednjeg kišovitog dana, što je otprilike vreme potrebno da se postigne zasićenost, insolacija pada za samo 3.1% u gradu Skadru, dok pad insolacije u gradu Tirani iznosi 8.5 % na lokaciji FEE i 18.4% na lokaciji FEMEP. Podaci pokazuju da je smanjenje insolacije blisko povezano sa antropogenom aktivnošću, prvenstveno saobraćajem oko mesta na kojem se nalazi meteorološka stanica. Razlika iz dana u dan ima tendenciju smanjenja sa povenjem broja dana IV MKOIEE 75

2 koji su prošli od poslednjeg kišovitog dana, što je dokaz tendecije ka dinamičkoj ravnoteži između procesa odvajanja aerosola tokom noći i njihovo stvaranje tokom dana. Ključne reči: insolacija tokom vedrog dana, antropogeni aerosoli, potencijal solarne energije, vremenska zavisnost insolacije Change of irradiative properties of the atmosphere during clear days is an indicator, among others, of existence of atmospheric aerosols and can be used as an indicator for assessment both air pollution and local modifications of solar energy potentials. The main objective of this study is estimation of influence of anthropogenic aerosols on solar energy falling in a horizontal surface during a clear day in the city of Tirana. We have analyzed and quantified the effect of aerosols on reducing the amount of solar energy that falls on the horizontal ground surface in cloudless sky conditions, estimating temporal evolution, both in daily and hour scale, considering also, side effects caused by relative humidity of the air wind speed and geometric factor. In order to determine the presence of aerosols in atmosphere, we agreed to use the attenuation of solar radiation after the last rainy day. Solar radiation received on a horizontal surface affected by some parameters: relative humidity, aerosols, and geometric factors. All data were corrected by factors such as, variations of relative humidity, wind speed and geometrical factors such as the slope of the surface and daily change of incident angle of solar radiation. We studied the change of solar insolation in three sites with different traffic intensity, one site in city of Shkodra and two sites in city of Tirana. Fifteen days after last rainy day, approximate time needed to achieve saturation, the insolation drops only 3.1% in the city of Shkodra, while the drop of insolation for city of Tirana is 8.5 % in the site of FEE and 18.4% at the site of FEMEP. The data show that reduction of solar insolation is closely related with anthropogenic activity, mainly traffic around the site of the meteorological station. The day to day difference tends to decrease with increasing of number of days passed from the last rainy day, which is an evidence of a trend toward a dynamic equilibrium between decantation process of aerosols during the night and their generation during the day. Key words: clear day insolation, anthropogenic aerosols, solar energy potential, time dependence of insolation. INTRODUCTION When solar radiation transfers through clear skies, it is damped by five basic processes, Rayleigh scattering, aerosol extinction, ozone absorption, water vapor absorption and permanent gases absorption. [1] 76 IV MKOIEE

3 Aerosols have an uncertain effect on climate and serious impacts on human health. Aerosols directly affect climate by modifying Earth s energy budget, known as irradiative forcing. Aerosols also modify cloud microphysical properties and albedo and thus impact precipitation (indirect irradiative effects). Aerosol particles result from different sources and processes. At any place in the atmosphere there exists a mixture or composite of particles of different origin. To describe the wide range of possible compositions, the aerosol particles are modeled as a combination of basic elements or components. Each aerosol component is described by an individual particle size distribution and spectral refractive index. The particles are considered to be spherical so that the classical Mie theory can be applied, although it is known that the exact shape and the orientation of the particles can significantly influence the irradiative properties. Water is important too, since it is ubiquitous in the atmosphere and interacts with aerosols. Therefore, the aerosol effects on climate also depend on the aerosol interaction with water and on its availability. For this, the relative humidity change has been taken into account in the interface. Relative humidity increases affect hygroscopic aerosols-nitrate, sulfate, sea salt, and a fraction of the organic carbon in a twofold way. On the one hand, an increase in relative humidity makes the particle size grow. Also it affects the hygroscopic aerosols optical properties by modifying the refractive index. As a result, the extinction coefficient increases with relative humidity. Hence, hydrated aerosols will exert larger irradiative perturbation than their dry counterparts [2]. Aerosols loading, or amount in the atmosphere, are usually quantified by mass concentration or by an optical measure, aerosols optical depth [3] Present measurement capabilities permit determination of the global annual average cloud-free aerosol for solar radiation. One of the major difficulties in retrieving aerosol properties from sky radiance is the screening of partially cloud-contaminated data. [4] Therefore, if aerosol amount changes over time, it would be very important to partition the change between anthropogenic and natural ones. [5] Solar energy is typically acknowledged as an important renewable energy source for the future in many countries. Radiation measurements are generally available for hourly intervals on horizontal surfaces. In order to determine the hourly incident radiation on a surface of any orientation, it is necessary to evaluate the ratio of incident radiation on the tilted surface to that on a horizontal surface considering beam, sky diffuse, and ground reflected radiation separately. Evaluating beam radiation on a tilted surface requires knowledge of the position of the sun relative to both the surface normal and vertical. The incident sky diffuse and ground reflected radiation depend upon the view factors between the surface and the sky and the surface and the ground. Both factors are functions of the position of the surface relative to the horizontal. The geometry necessary to analyze the problem is described in terms of three angles as shown in Figure 1. The slope of the surface, β, is the angle between the surface normal and the vertical. The incidence angle, θ, is measured between a ray from the sun and the surface normal. The zenith angle, θz, is the angle between the vertical and a ray from the sun (i.e. the incidence angle for a horizontal surface) [6]. The knowledge of the irradiance level for a site is a prerequisite to any setup of a solar power IV MKOIEE 77

4 system. The apparent position of the sun relative to the plane on the ground is dynamic depending on several geometric parameters. The declination angle δ can be determined from the equation: n δ = 23.45sin(360 x ) (1) 365 Where n is the number of day of the year in Julian calendar, 1 n 365, starting from 1 January. For a solar absorber in the Northern Hemisphere, if its frontal surface is intended to be positioned normally to the incident ray during solar noontime to intercept the solar radiation maximally, the slope of the absorber is: βz, noon = ϕ δ (2) Where β z, noon is the slope of the frontal surface of absorber at noontime and φ is the latitude angle of location with north positive, equator zero and south negative. The general relationship among the parameters of declination, latitude, slope, surface azimuth angle, hour angle and the angle of incidence of beam radiation is defined as below [1]: cosθ = sinδsinϕcos β sinδcosϕsin βcosγ + + cosδcosϕcos βcosω + cosδsinβsinγsinω where θ is the angle of incidence of beam radiation, β is the slope, γ is the surface azimuth angle (measured at zero due south, west positive and east negative) and ω is the hour angle (15 per hour displaced from local meridian; morning negative, afternoon positive).[7] MEASURING SYSTEM AND METHOD Atmospheric aerosols influence the Earth s climate by modifying its energy balance through the direct, indirect and semi-direct effects. However, the uncertainty of aerosol effects on the Earth s radiation budget greatly exceeds that of any other climate forcing agent. This is due to the fact that the aerosol physical, chemical and optical properties are highly variable in space and time, because of the short atmospheric lifetime of aerosols and of their inhomogeneous emissions. [8] Aerosol particles absorb and scatter the incoming shortwave radiation reducing the surface solar radiation. All long-term changes in aerosol content in the atmosphere will trigger changes in solar radiation flux. However this kind of assessments has high uncertainty mainly due to the following reasons: 1. The complex refractive indices of aerosols with different composition and size/shape at given wavelength is not known; 2. The vertical profile of particle shape and size distribution is not known; 3. The concentration of aerosol in the atmosphere has strong local character, and the direct and indirect aerosol measurements are very sporadic. (3) 78 IV MKOIEE

5 Figure 1. Geometry necessary for determining cloudless incident radiation 23, , , , Number of days after last rainy day Energy kwh/d Figure 2. Variation of energy on a horizontal surface in sky days, with number of days passed from last rainy day. The changes with the same sign (either increasing or decreasing) in solar and diffuse radiation are caused by the significant scattering of aerosol particles in cloud-free atmosphere. [9] Solar radiation is calculated by numerical models, which are parameterized by a set of inputs characterizing the cloud transmittance, state of the atmosphere and terrain conditions. [10, 11, 12] Stochastic variability of clear-sky atmospheric conditions is determined by changing concentrations of atmospheric constituents, namely aerosols, water vapor and ozone. The calculation accuracy of the clear-sky irradiance, especially DNI (Direct Normal Irradiance), is sensitive to the information about aerosols. The aim of this study is to determine the level of anthropogenic aerosols in urban areas. We have analyzed and quantified the effect of aerosols on reducing the amount of solar energy that falls on the horizontal ground surface in cloudless sky conditions, estimating temporal evolution, both in daily and hour scale, considering also, side effects caused by relative humidity of the air wind speed and geometric factor. In order to determine the presence of aerosols in atmosphere, we agreed to use the attenuation of solar radiation after the last rainy day. Solar radiation received on a horizontal surface affected by some parameters: relative humidity, aerosols, and geometric factors. We agreed to use the transmittance of the air after a heavy rain period as a reference zero day cloudless sky transmittance. Following days were counted as days after the last heavy rain period. To point out the impact of aerosols on solar radiation falling on a horizontal surface, we have take into account even impact of relative humidity, wind speed and geometric factors. After evaluation of each contribution on solar radiation, we must correct these contribution to highlights the effect of aerosols in atmosphere on solar radiation. The data analyzed were collected by three meteorological stations: the meteorological station of FEE (Faculty of Electrical Engineering) situated at the height of 20 m over the ground on top of the Main Building of Polytechnic University of IV MKOIEE 79

6 Tirana (41 o 19 4 N, 19 o E); the meteorological station of FEMEP (Faculty of Engineering Mathematics and Engineering Physics) situated at the height of 20 m over the ground on top of a building close to Faculty of Engineering Mathematics and Engineering Physics, Tirana(41 o 19 4 N, 19 o E); the meteorological station of FNS (Faculty of Natural Sciences) situated on top of the building of University of Shkodra, Shkodra (45 o N, 19 o E). The distance between meteorological station of FEE and FEMEP is nearly 1, 5 kilometers. While the meteorological station of FEE is situated near a green park the meteorological station of FEMEP is situated in a region with intensive cars traffic. Meteorological station of FNS is situated in a smaller city near a big lake and not very intensive cars traffic. Meteorological parameters used in our study, it is solar insolation, relative humidity of the air, wind speed and rain rate, were measured using a Davis Vantage Pro2 weather station in each location mentioned above. We have seen the dependence of solar energy versus the number of days after the last rainy day for each meteorological station. Correlation coefficients increases when these dependencies are corrected by relative humidity, wind speed and incident angle. Figure 2 shows a typical variation of energy on a horizontal surface in cloudless sky days, together with corresponding trend lines and correlation coefficients, with number of days passed from last rainy day. The best approximation trend lines for all data are power functions. Curve 1 - uncorrected, curve 2 - corrected for relative humidity and wind speed, curve 3 - corrected for relative humidity wind speed and incident angle, with correlation coefficients respectively R 2 = 0.581, R 2 = 0.602, R 2 = IV MKOIEE RESULTS AND DISCUSSION Reduction of solar energy budget The design and performance of solar energy systems for many potential applications (industrial/residential heat, electricity generation) will be critically affected by local insolation conditions. In addition to potential effect on global irradiative budget of the earth atmosphere system, aerosols have a significant impact on smaller scale by affecting the energy budget of both the layer in which they are present and the surface. [13, 14, 15] Assuming that aerosols have relative constant characteristics such as chemical composition, size distribution, vertical mass concentration and optical properties, reduction of solar irradiative budget is related only with increase of their concentration in the atmosphere. Direct observations of effect of regional aerosols on irradiative budget are scarce. [16, 17, 18] We studied the effect of urban air pollution on solar irradiative budget in two sites of the city of Tirana situated nearly 1.5 kilometers apart, but with very different traffic intensity, and in city of Shkodra situated near a big lake and low traffic intensity. This makes three sites to differ on anthropogenic activity. Assuming the atmosphere of the day after intensive rains as a clean atmosphere, it is the atmosphere with minimal concentration of the aerosols and highest irradiative budget, any reduction of insolation in following cloudless days,

7 as shown in Part one of this study [19], is caused by increase of aerosol concentration in atmosphere. Figure 3 shows the Variation of energy on a horizontal surface in cloudless sky days, with number of days passed from last rainy day. Measurement was performed during twenty one consecutive days, June 2012 in meteorological station of Shkodra. Data was corrected for relative humidity, wind speed and incident angle θ. Trend line best fitting the data for evening insolation was a power function of the form: Em Coefficient of correlation is R 2 = N = * (5) Energy kw/d 8,1 8 7,9 7,8 7,7 7,6 7, Number of days after last rainy day Figure 3. Variation of energy on a horizontal surface in cloudless sky days, with number of days passed from last rainy day 0,25 0,2 Relative reduction of energy 0,15 0,1 0, Number of days after last rainy day Figure 4. Relative reduction of insolation on a horizontal surface in a cloudless sky after different days from last rainy day Anthropogenic impact on solar radiation falling on a horizontal surface Solar energy falling in unit area of horizontal surface during the first day after last rainy day is taken as reference value of insolation of clean atmosphere. Relative reduction of insolation is calculated as difference of clean atmosphere insolation with insolation of the day N divided with clean atmosphere insolation. Relative reduction of energy is calculated for each meteorological station. In Figure 4 are shown relative reductions of insolation on a horizontal surface in a cloudless sky after different days from last rainy day for each station. Curve 1 shows relative reduction of energy in city of Shkodra. Trend line best fitting the data for evening insolation was a power function of the form: E1 E Coefficient of correlation is R 2 = Where: E N 1 ( ) = 0.011Ln N (7) IV MKOIEE 81

8 E 1- The energy in the first day E N- The energy on the Nth day Curve 2 shows relative reduction of energy in city of Tirana, meteorological station of FEE. Trend line best fitting the data for evening insolation was a power function of the form: 82 IV MKOIEE E 1 E E N 1 ( ) = 0.031Ln N (8) Coefficient of correlation is R 2 = Curve 3 shows relative reduction of energy in city of Tirana, meteorological station of FEMEP. Trend line best fitting the data for evening insolation was a power function of the form: E 1 E E N 1 ( ) = 0.067Ln N (9) Coefficient of correlation is R 2 = It worth to note that ground solar radiation budget is considerably affected by changes concentration of aerosols. From the Figure 4, it seems that the relative reduction of energy has a faster saturation at the meteorological station of Shkodra, compared with time of saturation in the sites of both meteorological stations in Tirana. Fifteen days after last rainy day, approximate time needed to achieve saturation, the insolation drops only 3.1% in the city of Shkodra, while the drop of insolation for city of Tirana is 8.5 % in the site of FEE and 18.4% at the site of FEMEP. The above data show that reduction of solar insolation is closely related with anthropogenic activity, mainly traffic around the site of the meteorological station. CONCLUSIONS Use of solar radiation on a horizontal surface during a cloudless sky day can be a useful method to monitor changes in aerosols density in near atmosphere. We applied this method for the first time to monitor the atmosphere in Tirana. There is uncertainty in distinguishing natural from anthropogenic aerosols. The reason is that natural and anthropogenic aerosols have different proportions of fine and coarse aerosols. However one of main characteristics of anthropogenic aerosols is their time dependence, it is their dependence on the human activity which is the source of aerosols. Concentration of aerosols in atmosphere reduces ground insolation, affecting the solar energy budget. We studied the change of solar insolation in three sites with different traffic intensity, one site in city of Shkodra and two sites in city of Tirana. Fifteen days after last rainy day, approximate time needed to achieve saturation, the insolation drops only 3.1% in the city of Shkodra, while the drop of insolation for city of Tirana is 8.5 % in the site of FEE and 18.4% at the site of

9 FEMEP. The above data show that reduction of solar insolation is closely related with anthropogenic activity, mainly traffic around the site of the meteorological station. The day to day difference tends to decrease with increasing of number of days passed from the last rainy day, which is an evidence of a trend toward a dynamic equilibrium between decantation process of aerosols during the night and their generation during the day. ACKNOWLEDGEMENTS We gratefully acknowledge Faculty of Electrical Engineering (FEI) for providing the meteorological data used in this study. A special appreciation goes to Prof. Dr. Nako Hobdari, Head of Department of Electrical Power Systems. REFERENCES [1] Kun Yang, and Toshio Koike, Estimating Surface Solar Radiation from Upper-Air Humidity [2] R. Pedrós, J.L. Gómez-Amo, C.R. Marc os, M.P. Utrilla s, S. Gandía, F. Tena, and J.A. Martinez Lozano AERO gui, A Graphical User Interface for the Optical Properties of Aerosols [3] B. Idso, Solar Radiation Measurements Augment Air Pollution Studies Sherwood [4] Atmospheric Pollution, [5] Aerosols properties and their impact on climate. Climate Change Science Program (CCSP) and mandated by the National Research Council (NRC), 2009 [6] J. E. Braun and J. C. Mitchellt, Solar Geometry for Fixed and Tracking Surfaces [7] Khai Mun Ng, Nor Mariah Adam, Othman Inayatullah and Mohd Zainal Abidin Ab Kadir, Assessment of Solar Radiation on Diversely Oriented Surfaces and Optimum Tilts for Solar Absorbers in Malaysian Tropical Latitude [8] C. D. Papadimas, N. Hatzianastassiou, C. Matsoukas, M. Kanakidou, N. Mihalopoulos, and I. Vardavas, The direct effect of aerosols on solar radiation over the broader Mediterranean basin [9] B. Bartók, Changes of aerosol radiative effect on clear sky solar radiation over Europe [10] Cebecauer T., Šúri M., Perez R., High performance MSG satellite model for operational solar energy applications, ASES National Solar Conference, Phoenix, USA, 2010 [11] Šúri M., Cebecauer T., Perez P., Quality procedures of Solar GIS for provision site-specific solar resource information, Conference Solar PACES 2010, September 2010, Perpignan, France [12] Cebecauer T. Šúri M. Accuracy improvements of satellite-derived solar resource based on GEMS re-analysis aerosols, Conference Solar PACES 2010, September 2010, Perpignan, France IV MKOIEE 83

10 [13] K. Lee and C. E. Chung, Observationally-constrained estimates of global fine-mode AOD Atmos., Chem. Phys., 13, , 2013 [14] Forster BC Derivation of atmospheric correction procedures for LANDSAT MSS with particular reference to urban data. Int J Remote Sensing 5: , 1984 [15] JA. Remote sensing digital image analysis: an introduction, Springer, Berlin, 1993 [16] Y. Fouquart, B. Bonnel, G. Brogniez, J.C. Buriez, I. Smith, J. J. Morcrette, A Cerf Observation of Sahara Aerosols: results of ECLATS Field Experiments, Part II, Journal of Climate and Applied Meteorology, Volume 26, pp 38 (1987) [17] Hussein A Kazem, Tamer Khatib, K. Sopian, Frank Buttinger, Wilfried Elmenreich, Ahmed Said Albusaidi, Effect of Dust Deposition on the Performance of Multi-Crystalline Photovoltaic Modules Based on Experimental Measurements International Journal Of Renewable Energy Research Hussein A Kazem et al., Vol.3, No.4, 2013 [18] Vijayakumar S. Nair, K. Krishna Moorthy, and S. Suresh Babu S. K. Satheesh, Optical And Physical Properties of Atmospheric Aerosols Over the Bay of Bengal During Icarb, Journal of The Atmospheric Sciences, Volume 66, Pp [19] U. Buzra, P. Berberi, D. Mitrushi, V. Muda, D. Halili, I. Berdufi, An estimation of impact of anthropogenic aerosols in atmosphere of Tirana on solar insolation, Part I: Clear day variation of ground insolation 84 IV MKOIEE