Research Article the Relation of Meteorological Elements with AOD for Building Energy Consumption

Hindawi Advances in Meteorology Volume 2018, Article ID 3584715, 20 pages https://doi.org/10.1155/2018/3584715

Research Article The Relation of Meteorological Elements with AOD for Building Energy Consumption

Hong Soo Lim and Gon Kim

Department of Architectural Engineering, Kyung Hee University, Yongin 446-701, Republic of Korea

Correspondence should be addressed to Gon Kim; [email protected]

Received 12 July 2017; Accepted 11 October 2017; Published 10 January 2018

Academic Editor: Gabriele Curci

Copyright © 2018 Hong Soo Lim and Gon Kim. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Tis study presents statistical relationships between various meteorological elements in Seoul city. It also discusses the vitality of the obtained relationship on the modelling of building energy consumption. Te data utilized in statistical evaluations was obtained from the archives of the Korean Meteorological Agency (KMA) for a period of four years. Another set of data was derived from state- of-the-art equations. Te used elements aside from aerosols are used for analysis in building energy simulations. For each weather element in the study, frequency and a monthly average are presented. Furthermore, statistical correlations are presented: solar radiation and temperature, solar radiation and sky cover, and solar radiation and aerosol optical depth (AOD). Te results indicate that the common assumption of a direct relationship between temperature and solar radiation is rather incorrect. In addition, whereas high solar altitudes are usually associated with high levels of solar radiation, the obtained results indicate a relatively weak 2 relationship between the two variables (� = 0.463). Te obtained results are proof that the efect of meteorological elements on, say, a building is not a single direct efect from a single variable but rather a combination of relationships between variables, which then produce a single efect.

1. Introduction might be helpful in determination of which solar control to use or during the sizing of HVAC systems. Fortunately, Buildings consume a signifcant amount of energy. In the US anumberofbuildingssimulationstoolshavebecomevery alone, it is estimated that the building sector consumes about common recently. Trough these tools, a lot of information 40% of the total energy produced [1]. Similar numbers are in regard to the behavior and performance of a space can noticedaroundtheworld.Giventhenatureoftheenergy be deduced in the design stages. Tese building simulations sources currently being utilized and the efect they have on tools rely on developed algorithms, weather, and climatic the environment, it is important that endeavors to reduce data as well as other user-specifed data such as occupant energy consumption in all sectors are taken seriously. behavior data and the thermal properties of building elements Architectsandscholarshavemaderecognizableefortin to predict the behavior of a given building, for instance, a reducing building energy consumption. Numerous passive building’s total heating or cooling load. strategies to reduce the dependency of buildings on the main- However, just like most sofware-based programs, the stream energy are being used today. Good examples for such accuracy of predicted results from building simulation tools practices include solar shading and cross ventilation. Tese is highly dependent on the input data, especially weather kinds of practices have contributed massive strides in the data. In the past, the weather input data only considered reduction of building energy consumption. However, such basicweatherfactorssuchassolarradiation,humidity,and passivestrategiesbecomeevenmorehelpfulwhencoupled wind speed. However, recently, almost all building simulation with the ability to predict the behavior of a building prior tools allow for the input of a much more detailed weather to actual construction; for instance, knowledge regarding the data fle that includes complicated elements such as ground thermal behavior of a given space during the design stage refectance and turbidity levels. Even though current building 2 Advances in Meteorology simulation tools consider a wide set of weather elements, radiation and the current study adopts the solar constant many more climatic factors need to be considered to improve valuesuggestedbytheWorldRadiationCenter(WRC).Te 2 the accuracy of the simulated results. In addition, scientifc WRC suggests a value of 1367 W/m ,withanuncertaintyof studies focusing on the relation of climatic conditions in the order 1% [3]. regard to building energy consumption are rather insuf- Assuming there is a sphere that covers the sun completely, cient. Terefore, this study, through a statistical approach, diameter between the earth and the sun would have an 11 discusses the relationship between several weather elements average distance of 1.5 × 10 m. Te distance from the sun fortheclimateofSeoulcity.Tevariablesdiscussedcanbe increases as radiant intensity decreases following the inverse easily summarized in three basic categories: weather data, square law. Te intensity of solar energy from an incoming solar radiation, and aerosols. Weather data include dry- light that falls on a perpendicular plane can be derived from bulb temperature dew-point temperatures, relative humidity, total solar radiation and the area of the imagined sphere. atmospheric station pressure, wind speed, wind direction, Tisradiationenergycanthenbeusedtocalculatethesolar total sky cover, visibility, and precipitable water. Solar radi- constant value which is adduced by the World Radiation ation includes extraterrestrial horizontal radiation, extrater- Center (WRC) as shown by (1) [4] restrial direct radiation, horizontal infrared radiation, global horizontal radiation, direct normal radiation, and difuse 3.865 × 1026 3 W = 1367 / 2, radiation. Aerosols include SO2 (ppm), PM10 (�g/m ), O3 2 W m (1) 4� (1.5 × 1011 ) (ppm), NO2 (ppm), CO (ppm), and AOD (aerosol optical m depth). Te results obtained in the current study would be of 0.033 360� =� (1 + cos ) signifcant importance to building simulation tool developers ER sc 365 whowishtounderstandtherelationshipbetweenvarious (2) meteorological elements and their efect on building energy made by Spencer (1971) , modelling. =� (1.000110 + 0.034221 � + 0.001280 � ER sc cos sin 2. Literature Review + 0.000719 cos 2� + 0.000077 sin 2�) (3) 2.1. Interrelationship between Solar Radiation and Architecture made by Iqbal (1983) , 2.1.1. Extraterrestrial Solar Radiation. Te radiation emitted (�−1) 360 �= . (4) by the sun to the outer space is of a consistent attenuation 365 unlike that emitted to the earth’s atmosphere. Tere are diverse methods used in calculating solar radiation. Some of Te extraterrestrial radiation utilized in the current study is these methods are based on developed theories and concepts, basedonamethodologydevelopedthroughtheapplication whileothersarebasedonactualdataobtainedfromsatellites. of Iqbal equations. As indicated here, 96.3% of solar irradi- For this study, an equation based methodology is adopted ance falls between 200∼2500 nm. It is worth emphasizing that in assessing the relationship between variables as well as the energy from the sun, is what is perceived as heat and evaluating energy consumption. Tis is because the data light here on earth. Solar or short-wave radiation is radiation required by the current study is unavailable in a real-time originating from the sun, in the wavelength range of 0.3 to form. 3 �m. It includes both beam and difuse components. On the Electromagnetic energy remains constant as it passes other hand, long-wave radiation is radiation originating from through the universal space and reaches the earth. Tis is the sources at temperatures near ordinary ambient temperatures reason why solar radiation reaching the outer space carries and thus substantially all at wavelengths greater than 3 �m. the same energy and wavelength as it had when leaving the Long-waveradiationisemittedbytheatmosphere,bya surface of the sun. However, the intensity of such a radiation collector, or by any other body at ordinary temperatures [5]. decreases as it is largely afected by the distance where it Te region with the strongest intensity has a maximum moves further away from the sun. Extraterrestrial radiation wavelength ranging from 400 nanometers to 600 nanome- has constant data for a year as there are no many obstacles ters. It has a major infuence on the ozone, water existing in such as those present in the earth’s atmosphere (Figure 1). the atmosphere, CO2, and a region called the daylighting zone As such, extraterrestrial radiation can be determined using by aerosols (380–780 nanometers) [6]. (1)–(4). Equation (2) was developed by Spencer in 1971. It In order to convert the outer space sunlight into extrater- considers a solar constant and dates in its calculations. Equa- restrial horizontal radiation (EHR), the equation below is tions (3) and (4) were developed by Iqbal in 1983. It follows used. Equation (7) is also used to calculate the ratio of a methodology that calculates extraterrestrial radiation by extraterrestrial horizontal radiation (EHR) to Global Hor- solar constant. izontal Radiation (GHR). At any point in time, the solar � Solar constant ( sc) refers to the energy from the sun radiation incident on a horizontal plane outside of the per unit time reaching a unit area of a surface perpendicular atmosphere is the normal incident solar radiation as given by to the direction of propagation of the radiation at mean earth-sun distance outside the atmosphere (see (1)). Te solar 360n � EHR =� (1 + 0.033 cos ) cos ��, (5) constant ( sc) is a critical factor in calculating extraterrestrial sc 365 Advances in Meteorology 3

Ts = 5777K 4 E=Ts Sun

9 1.39 × 10 m

Distance is 11 = 1.495 × 10 m ±17%

Short wavelength radiation (∝1/Ts, Wien's displacement law) Extraterrestrial region

／ ,＃／ ,（／, ＃／, Atmosphere 2 2 2

(porous media) ３／2,／3,．／2, PM10 (sulfuric acid)

32 Terrestrial Diﬀuse radiation region Beam radiation Long wavelength radiation (∝1/TE, TE ≪TS) Solar constant G Ｇ2 sc = 1367 W/

Earth

7 Diam. = 1.27 × 10

Figure 1: Behavior of solar radiation within the extraterrestrial and terrestrial regions.

=� (1 + 0.033 360n) the latitude, declination, and sunset hour angle instead of the EHR sc cos 365 (6) zenith angle. ⋅ (cos Φ cos � cos �+sin Φ sin �) GHR Global Horizontal Radiation = × 100. (7) EHR Extraterrestrial Horizontal Radiation � (see [3]), where sc (solar constant) is a measurement of fux density per unit area that would be incident on a plane In order to calculate how much sunlight attenuation is perpendicular to the rays and � is the day of the year. Φ brought upon by the atmosphere, the current study utilized (latitude) is the angular location north or south of the equator, the GHR/EHR ratio, which is the ratio of extraterrestrial ∘ ∘ north positive; −90 ≤Φ≤90 , � (declination) is the angular horizontal radiation to terrestrial radiation (global horizontal position of the sun at solar noon (i.e., when the sun is on radiation). To obtain the ratio, the values of GHR and EHR are frst determined. Te EHR values are computed the local meridian) with respect to the plane of the equator, ∘ ∘ by (5). Tis is because the solar radiation penetrates the north positive; −23.45 ≤Φ≤23.45 , �� (zenith angle) is the outer space without coming in touch with the atmosphere angle between the vertical and the line to the sun, that is, the andthusisunafectedbytheatmosphericmedium.Asfor angle of incidence of beam radiation on a horizontal surface, � the GHR, which indicates the amount of radiation coming and (sunset hour angle) is the hour angle at either sunrise to the terrestrial surface through the atmosphere, the study (when negative value is taken) or sunset (when positive value adopted hourly meteorological data collected by the Korea is taken). Meteorological Administration (KMA). GHR can also be Equation (2) (ER) multiplied by cos �� (zenith angle) defned as the sum of direct radiation and difuse radiation. produces extraterrestrial horizontal radiation and is referred As such, GHR values are largely afected by the distribution to as (5). Tis means that (5) can be represented by (6) using percentage of the two elements (direct and difuse radiation). 4 Advances in Meteorology

Sun

Extraterrestrial normal radiation

EHR Extraterrestrial direct radiation Normal  al

Horizont Beam  radiation Earth Direct normal radiation  Direct radiation Normal  GHR Beam radiation  ( − ) Equator

Figure 2: Concept behind the GHR/EHR equation.

Te GHR/EHR ratio determined by (7) is calculated as and difuse radiation, before the analysis is conducted. Te a percentage and is largely dependent on the distance of EnergyPlus sofware used in the current study behaves in transmission as well as the atmospheric conditions. Te ratio such a way as well. is used to indicate the infux of radiation in the terrestrial Te separating method of direct and difuse radiation surfaceandwithinbuildingssoastohelpintheevaluation presented in the EnergyPlus manual [7] is the same method of the building thermal performance or brightness of the presented by ASHRAE. As in (8), extraterrestrial normal light reaching the inside of a building. Figure 2 explains the irradiance is divided into beam normal radiance and difuse concept behind the GHR/EHR equation. horizontal radiance by considering air mass and aerosol Figures 3 and 4 show the way the earth releases solar optical depth. Te air mass changes depending on the solar energy that it gains. Te fgure also shows that the amount altitude as indicated by (9). Consequently, the air mass is used of radiation that the earth gains is diferent from the amount as a variable of exponential function. that is reradiated and explain the data using percent scales. As In regard to the aerosol optical depth in (8), the fnal indicated in the fgure, when 114% of the energy is reradiated value is afected by other elements except for air mass. As a � � � into the atmosphere, only 18% manages to escape into the result, 0 is calculated by (5) and b and d calculated by the outer atmosphere. Tis means that 96% of reradiated solar exponential function are inversely proportional to the aerosol energy is absorbed by the atmosphere. optical depth and air mass. As such, the current study was conducted under the 2.1.2. Direct and Difuse Solar Radiation. Solar energy which assumption that aerosol optical depth is able to afect energy isthemainsourceofenergyonearthisdividedintotwo consumption in buildings as it has an efect on the solar portions: direct and difuse sunlight by the time it hits the radiation reaching the building earth. Te proportion of these two elements (difuse and direct sunlight) that the sun’s radiation carries afects the � =� [−� �ab] b 0 exp b behavior of buildings in regard to building thermal loads = 1.219 0.043� − 0.151� − 0.204� � , When the proportion of direct sunlight is large, there ab – b d b d is an increase in the amount of long wavelength infrared (8) � =� [−� �ad] reaching the building. Tis long wavelength infrared that is d 0 exp d known as thermal infrared raises the cooling load as a result = 0.202 0.852� − 0.007� − 0.357� � of the increased indoor heat gain. As such, energy simulation ad – b d b d computer sofware that is used to calculate thermal loads � through the analysis of solar radiation usually separates the (see [8]), where b is beam normal irradiance (measured � global horizontal radiation into two entities, beam radiation perpendicularly to rays of the sun), d is difuse horizontal Advances in Meteorology 5

Extraterrestrial incoming radiation

−25 percent 100 percent −7 percent

Reﬂected into space from clouds and dust Scattered in atmosphere

18 percent

Absorbed directly by atmosphere

16 percent +1 percent Loss due to albedo based on 10 percent of Absorption 15 percent of radiation by water and ice received of clouds

−5 percent Direct Diﬀuse Diﬀuse radiation radiation radiation +26 percent +14 percent +11 percent

Figure 3: Te ratio of absorption of solar energy by atmospheric elements (borrowed from buildings, climate, and energy by MARKUS) [2].

irradiance (measured on horizontal surface), �0 is extrater- 18 percent restrial normal irradiance, ab and ad are beam and difuse air Loss of radiation mass exponents (empirical relationships) to space Absorbed 1 and reradiated �=air mass: [ � + 0.50572 (6.07995 + �)−1.6364] back to earth sin (9) (made by Kasten and Young 1989) Atmospheric counterradiation � � � (see [8]), b and d are beam and difuse optical depths ( b and � are more correctly termed “pseudo” optical depths, d Radiation because optical depth is usually employed when the air from surface mass coefcient is unity; “optical depth” is used here for convenience), and � is the angle between the line deriving 114 percent 96 percent from the sun and the horizontal plane. Te values of � range from 0 to 90 degrees, 0 degrees when the sun is positioned at Figure 4: Te ratio of reradiation of solar energy by atmospheric ele- the horizon, and 90 when the sun is at the zenith. ments (borrowed from buildings, climate, and energy by MARKUS) Te air mass has an efect on the path taken by the solar [2]. beam from the moment it passes through the atmosphere to the moment it hits the earth. It is easy to see that �=0for the extraterrestrial space or for an earth lacking an atmosphere 2.2. Interrelationship between Solar [9]. Radiation and Architecture � � Values of b and d depend on the location and change variably according to the time over the year. Tey form the 2.2.1. Defnition of Aerosol Optical Depth. Aerosols are very link between solar radiation and other local conditions such small particles of gas and other tiny particles that foat in as elevation and aerosols. Te ASHRAE research project RP- the atmosphere. Te exact size of aerosols ranges from a 1453 (Tevenard 2009) was used to determine the average fraction of a micrometer to a few hundred micrometers. � � values of b and d. Te values were recorded for the 21st day Aerosols exist naturally. Also, their existence has been linked of every month for all locations in the tables of climatic design to anthropogenic sources such as volcanoes, dust, bacteria, � conditions. For the other days of the year, average values of b and dust. Aerosols have a huge impact on the weather and � and d canbefoundbyinterpolation[10]. climate that we experience here on earth as they are able to 6 Advances in Meteorology

I(s1)II(s) I(s + ds) (s2)

ExtinguishingE u g mediumu

s1 s s+ds s2

Figure 5: Change in solar radiation over an infnitesimal path �� within a medium. afect the amount of sunlight reaching the earth and thus the Te transmittance of radiation integrated over an optical abilityofaerosolstoblocktheamountofsunlightreaching path, �≪1,iscalculatedby the earth is measured in terms of aerosol optical depth �= (−�) ≈1−�(�,� )=1−� (� −� ). (AOD) or aerosol optical thickness (AOT). As the AOD at exp 1 2 � 2 1 (14) a given wavelength increases, the amount sunlight reaching In a case where a medium remains intact (albedo = 0), the the earth’s surface decreases. Such information is critical for remainder of the radiation that is not transmitted during the determining the availability of aerosols in the atmosphere as journey is absorbed. Te path absorbance is then given by well as their size and distribution [11]. Te concept of optical depth used in this study is described by adopting beer’s law, �=1−�, and the percentage of solar radiation transmittance achieved � (15) through the absorption and the scattering of solar radiation �= =�−�. � could decrease depending on the condition of the earth’s 0 atmosphere as illustrated by (17). Te coefcient of extinction If �0 and � represent the intensity of original light and the � denoted by the symbol ( �)isobtainedthroughthesumof intensity of transmitted light, respectively, then the value � the absorption coefcient denoted by the symbol ( �)andthe of � obtained by (14) on absorption coefcient represents � scattering coefcient denoted by the symbol ( �) “transmittance,” while � from (13) represents optical depth In this section, we recall beer law of optical depth from “a due to attenuation and light scattering. Te amount of frst course in atmospheric radiation” by Petty, Grant William transmittance is 60% if � valueis0.5and8%whenthevalueof Beer’s law of optical depth is represented by � is 2.5. Tere is need to integrate Beer’s law for an entire path � �� =�� +��. (10) through the atmosphere while considering the changes in � � asthelocationandthedirectionchange.Teintegralquantity Te absorption coefcient ( �) describes the amount of is the optical depth or optical thickness (when measured power attenuation that reaches a unit distance in a second. vertically in the atmosphere) or the optical path. It can have Te relationship between the absorption coefcient (��), ��, � any positive value. and wavelength ( )isrepresentedby Figure 5 explains the attenuation by dividing the atmo- 4�� sphere into small pieces and using integral calculus on each � = . (11) � � section as (16). Te calculated value (�) is optical depth (�) In a medium of a uniform nature, an initial intensity denoted and the transmittance value could be determined using the exponential function (see (17)). Terefore, the calculated by �0 the symbol at a position �=0and which increases in the �-direction is described by optical depth means attenuation coefcient with no scale. Figure 6 shows that function explaining the concept of optical −�� (�) =��,0� , depth

�2 � (�) −� (12) � �� (� )=� (� ) [− ∫ � (�) ��] , =� =�� (�) transmittance function, � 2 � 1 exp � (16) ��,� �1

� −�(�1,�2) where is the transmittance: the amount of solar radiation � (�1,�2) =� , (17) that remains afer travelling a certain distance � Transmittance ranges from near zero to one. Given that �=�� (�2 −�1), (18) the solar absorption coefcient is constant from points �1 to �2 then �(�1,��)=�(�1,�2)+�(�2,�3)+⋅⋅⋅+�(��−1,��), (19) �=� (� −� ) . � 2 1 Optical depth (13) �(� 1,��)=�(�1,�2)×�(�2,�3)×⋅⋅⋅×�(��−1,��). (20) Advances in Meteorology 7

Reﬂection

Direct radiation Diﬀuse radiation

I0 Absorption I(x)

Reradiation

Reﬂection Scattered radiation (reradiation)

Figure 6: Function explaining the concept of optical depth.

0.0 0.2 0.4 0.6 0.8 1.0

Figure 7: Global map of aerosol optical depth distribution. Available at https://earthobservatory.nasa.gov.

2.2.2. Measurement for Aerosol Optical Depth. Generally, where the coefcients �0, �1,and�2 were determined by a AOD is obtained by (21). Optical depth can be determined line of best ft from plotted ground data. Te current research using three methods: MODIS, MATCH, and AERONET adoptstheAODvalueoferedbytheAERONET. =�⋅�−�, AOD� (21) 3. Results where “AOD�” is a representation of the aerosol optical Tis section of the manuscript deals with weather elements depth at a given wavelength “�.” Tree categories of data that were studied in this manuscript. Statistical analyses regarding aerosols are utilized: (a) MODIS which is obtained of each of the weather elements are conducted. For each from space borne measurements using satellite pictures element, a monthly average and frequency are presented. obtained through NASA homepage such as Figure 7, (b) chemical model for MATCH, and (c) aerosol optical depth 3.1. Monthly Average and Frequency of data obtained through the MATCH and MODIS methods Weather Data in Seoul whichwerethencomparedwithdataobtainedfromactual ground sites. Most of this data was obtained through the 3.1.1. Monthly Average and Frequency of Temperature. In this AERONET network. For this particular study, data from chapter, we analyzed average and distribution values with 196 sites accumulated over a period of 3 years were used measured data from 2011 to 2014 (total 35,040). Hourly for a given month [12, 13]. Figure 7 was obtained from the weather data was divided by months and calculated maxi- Moderate Resolution Imaging Spectroradiometer (MODIS) mum and minimum values. run by the NASA’s Terra satellite. It shows aerosol optical Figure 8 shows hourly data from 2011 to 2014 in a depth distribution data for the month of September 2015. monthly graph with a total of 35,040 measured datasets. ∘ Also, data ofered by AERONET is used for ground based Te average dry temperature on the outside was 12.6 C, the ∘ sites. ASHRAE explained this concept using the equation standard deviation was 11.3 C, and minimum and maximum ∘ ∘ below. Measurements of AOD and precipitable water accu- values were −17.7 Cand36.2C, respectively. Te monthly mulated over a long period from the AERONET program distribution graph of dry-bulb temperature shows the July were analyzed together with an angstrom exponent and used andAugustmonthstobethehottest.Inwinter,typical to determine the properties of aerosol optical properties weatherdistributionwasthesamewiththatofSeoul,where ∘ on some days temperatures go below −10 C, and frequency =� +� ⋅ +� ⋅ , ∘ AOD 0 1 AODMATCH 2 AODMODIS (22) oftemperaturedistributionwasthehighestat20∼30 C. 8 Advances in Meteorology

40.0 1,200.0

30.0 1,000.0

20.0 800.0

10.0 600.0 Frequency .0 400.0 Dry-bulb temperatures

−10.0 200.0

−20.0 0.0 1 23456789101112 −20.0 −10.0 .0 10.0 20.0 30.0 40.0 (Month) Dry-bulb temperatures

∘ Figure 8: Monthly average and frequency of dry-bulb temperature (unit: C).

30.0 1,200

20.0 1,000

10.0 800

.0 600

−10.0 Frequency 400

Dew-point temperatures Dew-point −20.0 200 −30.0 0 −30.0 −20.0 −10.0 10.0.0 20.0 30.0 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Dew-point temperatures (Month) ∘ Figure 9: Monthly average and frequency of dew-point temperature (unit: C).

However, distribution frequency did not show a similar In case of monthly distribution of atmospheric pressure, distribution to that of a distribution curve. the average pressure was 100,586 Pa, standard deviation was In case of dew-point temperature as shown in Figure 9, 808Pa,andtheminimumwas97,510Pa,whilethemaximum ∘ ∘ the average was at 4.19 C, standard deviation was at 12.6 C, was 102,820 Pa (see Figure 11). Also, the average of atmo- ∘ ∘ and minimum and maximum were at −28.8 Cand26.9C, spheric pressure seems to decease during the summer period respectively. Also, distributions of dew-point temperature but increases gradually during the winter period. and dry-bulb temperature showed a similar trend. 3.1.3. Monthly Average and Frequency of Solar Radiation. 2 From the analysis, average was 628 Wh/m ,standarddevi- 3.1.2. Monthly Average and Frequency of Relative Humid- 2 2 ation was 384 Wh/m ,theminimumwas1Wh/m,andthe ity and Atmospheric Station Pressure. Te average relative 2 humidity was at 59.8%, standard deviation was at 19.9%, maximum was 1,280 Wh/m . And monthly result was not and the minimum was 9%, while the maximum was 100%. large (see Figure 12). In addition, the behavior of EHR is Relative humidity in the months of June, July, and August similar to that shown by outdoor temperature. was relatively larger, so we could anticipate that there are As shown in Figure 13, the extraterrestrial direct solar many hotter and moister days in summer. Unlike temper- radiation belonging to a particular location varies throughout ature distribution, frequency distribution relatively shows a the year. Te average of extraterrestrial direct radiation 2 2 fgure of normal distribution curve. Terefore, distribution was 1,367 Wh/m ,standarddeviationwas33Wh/m,and ∘ 2 of 23∼24 C which is the most pleasant temperature and the the minimum was 1,321 Wh/m , and the maximum was 2 appearance frequency of relative humidity 40∼60% were the 1,415 Wh/m . Extraterrestrial direct radiation presented large highest by calculating temperature distribution of Korea only variations from month to month and extraterrestrial direct with frequency of temperature and humidity (see Figure 10). radiation of the summer period was the lowest. Advances in Meteorology 9

100 800

80 600 60 400 40 Frequency Relative humidity Relative 20 200

0 0 0 20 40 60 80 100 120 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Relative humidity (Month) Figure 10: Monthly average and frequency of relative humidity (unit: %).

103000 1,000

102000 800 101000 600 100000

99000 Frequency 400

98000 200 Atmospheric station pressure station Atmospheric 97000 0 97000 98000 99000 100000 101000 102000 103000 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Atmospheric station pressure (Month) Figure 11: Monthly average and frequency of atmospheric station pressure (unit: Pa).

1,200 1250 1,000 1000 800 750 600

500 Frequency 400 250 200

Extraterrestrial horizontal radiation horizontal Extraterrestrial 0 0 0 250 500 750 1000 1250 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Extraterrestrial horizontal radiation (Month) 2 Figure 12: Monthly average and frequency of extraterrestrial horizontal radiation (unit: Wh/m ).

Global horizontal radiation is presented as a graph of study and difuse radiation were divided by PEREZ equa- 17,692 measured datasets without the night time values tion model using measured global horizontal radiation. Te which were not measured. Global horizontal radiation can be results of inside global horizontal radiation distribution were 2 defned as a sum of direct horizontal radiation and difuse calculated as follows: average of 275.3 Wh/m ,astandard 2 horizontal radiation. Direct normal radiation used in this deviation of 228.6 Wh/m , and a minimum and a maximum 10 Advances in Meteorology

1420 2,000

1400 1,500 1380 1,000 1360 Frequency

1340 500 Extraterrestrial direct radiation direct Extraterrestrial 1320 0 1320 1340 1360 1380 1400 1420 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Extraterrestrial direct radiation (Month) 2 Figure 13: Monthly average and frequency of extraterrestrial direct radiation (unit: Wh/m ). )

2 1200 2,000 Ｇ 1000 1,500 800

600 1,000

400 Frequency 500 200

0 Global horizontal radiation (W/ radiation Global horizontal 0 0 200 400 600 800 1000 1200 Jul Jan Jun Sep Feb Oct Apr

Dec 2 Mar Agu Nov May Global horizontal radiation (W/Ｇ ) (Month) 2 Figure 14: Monthly average and frequency of global horizontal radiation (unit: Wh/m ).

2 2 2 2 of 3 Wh/m and 1,008 Wh/m ,respectively(seeFigure14). 3Wh/m and the maximum 499 Wh/m (see Figure 16). Solar irradiance was expected to be the biggest because Unlike with direct normal radiation, difuse radiation seemed the solar altitude is the highest during the summer period. to increase in the frst 6 months of the year and gradually However,itsabsolutevaluewaslowduetothepresence decrease in the last 5 months of the years except for the month of high amounts of clouds and interference from other of July. Te direct normal radiation is lower than global atmospheric conditions. Tis shows that ground temperature horizontal radiation because the value of global horizontal cannot be explained by only solar energy values as global solar irradiation consists of a sum of direct normal radiation from radiation did not exactly coincide with temperature. the sun and the difuse horizontal radiation that has been Direct normal radiation refers to the quantity of solar scattered by clouds and other atmospheric particles. As such radiation reaching a unit surface of a given area when this subtracting the value of difuse normal radiation from the surface is positioned perpendicularly to the rays of the value of global horizontal irradiation gives us an expectedly sun. Te average value of calculated direct normal radiation lower value of direct normal radiation. 2 2 was 281 Wh/m and the standard deviation was 227 Wh/m , Te value of the ratio GHR/EHR is relatively smaller 2 while the minimum and maximum values were 1 Wh/m and duringthesummerperiodthanotherseasonsduetoa 2 856 Wh/m , respectively (see Figure 15). As expected, the decreasing global horizontal radiation. According to the measurement value in summer was relatively low and the analysisofthedata,theaveragevalueandstandarddeviation amount of solar radiation in winter was twice as high as the of GHR/EHR were 36% and 22%, respectively, while the radiation in summer minimum value was 0 and the maximum value was almost 100% (see Figure 17). Direct Direct = horizontal radiation . normal radiation ( ) (23) sin solarheight 3.1.4. Monthly Average and Frequency of Sky Cover and Hori-

2 zontal Infrared Radiation. Te amount of clouds measured by Te average difuse radiation was 161 Wh/m and stan- KMAmeansthepercentageofcoveredskyfrom0to10,where 2 dard deviation was at 119 Wh/m , while the minimum was 0 represents the absence of cloud cover and 10 represents Advances in Meteorology 11

1000 1,200

800 1,000

600 800

600 400 Frequency 400

Direct normal radiation normal Direct 200 200 0 0 0 200 400 600 800 1000 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Direct normal radiation (Month) 2 Figure 15: Monthly average and frequency of direct normal radiation (unit: Wh/m ).

500 1,200

400 1,000

800 300 600 200 Frequency 400 Diﬀuse radiation 100 200 0 0 0 100 200 300 400 500 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Diﬀuse radiation (Month) 2 Figure 16: Monthly average and frequency of difuse radiation (unit: Wh/m ).

100 2,000

80 1,500 60 1,000 40 Frequency GHR/EHR

20 500

0 0 0 100 200 300 400 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May GHR/HER (Month) Figure 17: Monthly average and frequency of GHR/EHR (unit: %). maximum cloud cover. Te result of analysis of the amount solar radiation reaching the earth. In other words, there exists ofcloudsshowstheaverageandstandarddeviationtobe4.81 a negative correlation between sky cover and sunlight. 2 and 3.93, respectively (see Figure 18). Also, the average of sky Te average horizontal infrared radiation was 638 Wh/m 2 cover is the highest during the summer period and thus a and the standard deviation was 318 Wh/m , while the mini- 2 2 possible indicator of the impact of sky cover on the amount of mum and the maximum were 171 Wh/m and 1,337 Wh/m , 12 Advances in Meteorology

10 12,000

8 10,000

8,000 6 6,000 4 Frequency

Total sky cover Total 4,000 2 2,000 0 0 0 36912 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Total sky cover (Month) Figure 18: Monthly average and frequency of total sky cover.

1,500 1250

1000 1,000 750

500 Frequency 500 250 Horizontal infrared radiation infrared Horizontal 0 0 0 250 500 750 1000 1250 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Horizontal infrared radiation (Month) 2 Figure 19: Monthly average and frequency of horizontal infrared radiation (unit: Wh/m ).

respectively (see Figure 19). Te average value of June, July, 3.1.6. Monthly Average and Frequency of Aerosol Optical Depth andAugustwhichisthehottestseasonshowedthehighest and Precipitable Water. According to the 2014 annual report intensity of horizontal infrared radiation and generally it of air quality in Korea from the Ministry of Environment showed results closest to theoretically expectations. Although [14], in the case of SO2 of Seoul, annual mean pollution level the temperature had many right sided result values from the tended to decrease; however, it showed no change from 2002 center of normal distribution, horizontal infrared radiation to 2009. Although the average of pollution level from 2010 to had a higher frequency at the lef side of the center. 2012 is 0.005 ppm, the average pollution levels in 2013 were 0.006 ppm, which is a 0.001 ppm increase from the year 2012. 3.1.5. Monthly Average and Frequency of Wind Speed and In the past four years, according to measured levels of Visibility. Te average wind velocity in Seoul was found to SO2, the monthly average of summer was lower than that be 2.74 m/s and had a standard deviation of 1.47 m/s. Te of winter and it showed similar tendencies with atmospheric minimumwindvelocitywas0,whilethemaximumwas pressure. Te quantitative result showed an average and 11.4 m/s. From the analyzed results, it is easy to see the absence standard deviation of 0.005 ppm and 0.003 ppm, respectively, of high velocity such as typhoons during the past four years as well as a minimum of 0.001 ppm and a maximum of (see Figure 20). 0.033 ppm (see Figure 22). Visibility is a meteorological element that shows the Nowadays, people are more interested in microaerosol turbidity of the atmosphere. Visibility of an atmosphere on due to the air pollution by the Asian dust phenomenon. a given day can be defned as the maximum distance from Microaerosol is divided into PM-10 and PM-2.5 based on which a person with normal vision can identify an object diameter. PM-10 is smaller than ten thousandths mm and placedonthegroundinbrightlightconditionssuchasduring PM-2.5 is smaller than 2.5 thousandths mm. Microaerosol is theday.Figure21showsthemonthlyaverageandfrequency the emission of a mixture of solid and liquid particles in the of visibility. air.Itcanalsobearesultofchemicalreactionsorsimplydue Advances in Meteorology 13

12.0 2,500

10.0 2,000 8.0 1,500 6.0 Frequency Wind speed 4.0 1,000

2.0 500

.0 0 .0 3.0 6.0 9.0 12.0 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Wind speed (Month) Figure 20: Monthly average and frequency of wind speed (unit: m/s).

3.0 12,000

2.5 10,000

2.0 8,000

1.5 6,000 Visibility

1.0 Frequency 4,000

.5 2,000 .0 0 .0 3.0 6.0 9.0 12.0 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May Visibility (Month) Figure 21: Monthly average and frequency of visibility (unit: km).

.0400 6,000

5,000 .0300 4,000

.0200 3,000 SO2 (ppm) Frequency 2,000 .0100

1,000 .0000 0 .0000 .0100 .0200 .0300 .0400 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May SO2 (ppm) (Month)

Figure 22: Monthly average and frequency of SO2 (unit: ppm). to natural causes. PM-10 repeatedly increased and decreased In the result of monthly data analysis of PM-10 with a 3 fuctuating within 51∼61 �g/m from 1998 to 2006, decreased total of 34,605 measured datasets except missing data, its 3 from 2007, and got lower to 54 �g/m in 2008. Ten it kept gap between maximum and minimum is the highest. Te 3 3 dropping until 45 �g/m in 2012 and increased from 45 �g/m averagevalue,standarddeviation,andtheminimumand 3 3 to 49 �g/m in 2013. maximum values of PM-10 were found to be 43.5 �g/m , 14 Advances in Meteorology

600 6,000

500 5,000 ) 3 400 4,000 g/ Ｇ  300 3,000 Frequency 200 PM-10 ( 2,000

100 1,000 0 0 0 100 200 300 400 500 600 Jul Jan Jun Sep Feb Oct Apr Dec

Mar 3 Agu Nov May PM-10 (g/Ｇ ) (Month) 3 Figure 23: Monthly average and frequency of PM-10 (unit: �g/m ).

5,000 .1250 4,000 .1000

3,000 .0750 O3

.0500 Frequency 2,000

.0250 1,000

.0000 0 .0000 .0250 .0500 .0750 .1000 .1250 Jul Jan Jun Sep Feb Oct Apr Dec Mar Agu Nov May O3 (ppm) (Month)

Figure 24: Monthly average and frequency of O3 (unit: ppm).

3 3 3 31.9 �g/m ,1�g/m ,and561�g/m in that respective order spontaneous generation such as a forest fre, kitchen, cigarette (see Figure 23). smoke, and district heating. It reduces the transporting capa- Te annual average of the pollution level of Seoul main- bility of hemoglobin by changing hemoglobin into carbonyl tained a certain level since 1998, but afer 2010, it increased by hemoglobin (COHb). Also a high concentration of carbon 0.001 ppm every year and it was at 0.026 ppm in 2013. monoxide is toxic and very harmful to human beings. As In the result of monthly data analysis of O3 with a total it turns out, CO shows a decreasing tendency from 1998 to of 34,605 measured datasets except for discrete missing data, 2014, while it showed maintained levels at 0.6 ppm from 2005 the average was found to be 0.02 ppm and standard deviation to 2008 and decreased slightly from 2009 to 2013 coming to was found to be 0.016 ppm, while the minimum was found at 0.5 ppm. 0.01 ppm and the maximum at 0.126 ppm (see Figure 24). IntheresultofmeasurementofCOwithatotalof34,630 NO2 becameworsefrom1998to2001,whileitmaintained measured datasets, the average was found to be 0.517 ppm a certain level from 2009 to 2012. It led to an increase in and the standard deviation was found to be 0.332 ppm, while averagepollutionlevelto0.026ppmfrom2007to2008.And the minimum and maximum stood at 0.1 ppm and 2.9 ppm, it decreased from 2009 to 2012 and increased again from respectively (see Figure 26). 0.001 ppm to 0.024 ppm in 2013. In the result of analysis of the Aerosols are solid and liquid tiny particles that foat in distribution of NO2 with a total of 34,428 measured datasets, the air. Teir sizes can range from 0.001 �mto100�m. Te the average amount of NO2 was found to be 0.035 ppm (see particles difuse and absorb sunlight, hence reducing the Figure 25). temperatures reaching the earth. Also, they can block people’s Carbon monoxide is a colorless and odorless toxic gas view and may lead to unusual weather conditions. which is generated at incomplete combustion. Its major Teresultsofanalysiswithatotalof8,138measured discharge source is transportation and it is also generated datasets that were obtained from AERONET showed an fromburningoffuelinindustrialprocesses.Tereare average of 0.653, a standard deviation of 0.606, and a Advances in Meteorology 15

2,000 .1200

.1000 1,500 .0800

.0600 1,000 Frequency NO2 (ppm) NO2 .0400 500 .0200

.0000 0 .0000 .0250 .0500 .0750 .1000 .1250 Jul Jan Jun Sep Feb Oct Apr Dec Mar Aug Nov May NO2 (ppm) (Month)

Figure 25: Monthly average and frequency of NO2 (unit: ppm).

3.0 6,000

2.5 5,000

2.0 4,000

1.5 3,000 CO (ppm) 1.0 Frequency 2,000

.5 1,000 .0 0 .0 .5 1.0 1.5 2.0 2.5 3.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 CO (ppm) (Month) Figure 26: Monthly average and frequency of CO (unit: ppm).

6.00 2,000

5.00 1,500 4.00

3.00 1,000 AOD

2.00 Frequency 500 1.00

.00 0 .00 1.00 2.00 3.00 4.00 5.00 6.00 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 AOD (Month) Figure 27: Monthly average and frequency of AOD.

minimumandmaximumvalueof0.032and5.64,respectively In the result of analysis of precipitable water distribution (see Figure 27). In the case of AOD, the data of June and July with a total of 5,959 measured data that was obtained from is relatively high and it did not show similar tendencies to AERONET, the average amount of precipitable water was previously analyzed airborne dust data. showntobe1.346cmandthestandarddeviationwasat 16 Advances in Meteorology

6.00 600

5.00 500

4.00 400

3.00 300

2.00 Frequency

Precipitable water 200

1.00 100 .00 0 .00 1.00 2.00 3.00 4.00 5.00 6.00 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 Precipitable water (Month) Figure 28: Monthly average and frequency of precipitable water (unit: cm).

Table 1: Correlation of temperature and solar radiation in cooling period.

Pearson correlation Variables Mean Std.deviation � (1) (2) (3) (4) (5) (6) ∘ (1) Dry-bulb temperatures ( C) 24.57 4.38 7956 1 ∘ ∗∗ (2) Dew-point temperatures ( C) 15.49 5.91 7956 .439 1 2 ∗∗ ∗∗ (3) Horizontal infrared radiation (Wh/m ) 861.50 284.21 7956 .111 .620 1 2 ∗∗ ∗∗ ∗∗ (4) Global horizontal radiation (Wh/m ) 298.99 245.29 7956 .289 −.350 −.410 1 2 ∗∗ ∗∗ ∗∗ ∗∗ (5) Direct normal radiation (Wh/m ) 148.65 190.64 7956 .107 −.444 −.615 .793 1 2 ∗∗ ∗∗ ∗∗ ∗∗ ∗∗ (6) Difuse radiation (Wh/m ) 195.10 133.45 7956 .344 −.196 −.178 .852 .402 1 ∗∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed).

1.066 cm, while the minimum and maximum amounts stood by the factors such as time lag on the earth. Also, negative at 0.077 cm and 5.75 cm in that order (see Figure 28). In the correlations shown between AOD, dew-point temperature, result of monthly observation, it showed the highest level in and solar irradiation could be attributed to the infuence of July and August and did not exceed 1 in the winter season. time lag or other variables. Table 1 shows the analysis of Trough these results, it can be concluded that the amount of the correlation between temperature and solar radiation in watervaporintheatmospherecontributestothedecreasein cooling period. solar radiation as it is the highest in June, July, and August. Te results obtained from analyzing the correlation between temperature levels during the heating period 3.2. Monthly Average and Frequency of Weather Data in Seoul (October–April) and solar radiation during daytime show no signifcant diference with that of the cooling period. On the 3.2.1. Statistical Correlation between Temperature and Solar contrary, certain data showed a declined correlation. Dry- Radiation. Te correlation analysis results between the tem- bulb temperature and beam radiation, diferent from cooling perature levels experienced during the cooling period (May to period, denote negative correlation, which means that there September) and solar radiation during daytime (from 7 a.m. is no correlation. Dew-point temperature and difusion solar to 7 p.m.) show that the correlation coefcient between total radiation both show negative correlation during the cooling solar radiation and dry-bulb temperature is no more than 0.3, period, but positive correlations were found during the and wet bulb temperature is inversely proportional to the total heating period. solar radiation. Correlation coefcient between difusion Relationship between horizontal infrared radiation and solar radiation and dry-bulb temperature is 0.344 and is solar irradiation shows a similar tendency, though the cor- 0.107incaseofbeamradiationanddry-bulbtemperature, relation value is slightly low. Tus, for the heating period, which is relatively low. Generally, dew-point temperature discordant results between the independent variables and has high correlation coefcients with dry-bulb temperature dependent variables were found, showing no correlation and horizontal infrared radiation that is usually higher than within variables. Table 2 shows the analysis of correlation of 0.4. However, correlation with dry-bulb temperature and temperature and solar radiation during the heating period. horizontal infrared radiation is exceedingly low at 0.111 in this case. Tis may be due at an error caused by the time 3.2.2. Statistical Correlation between Solar Radiation and lag. In the relation between dry-bulb temperature and beam Solar Altitude. Teoretically, the relationship between solar radiation, the correlation is also relatively underestimated radiation and solar altitude is dependent upon the angle of Advances in Meteorology 17

Table 2: Correlation of temperature and solar radiation in heating period.

Pearson correlation Variables Mean Std.deviation � (1) (2) (3) (4) (5) (6) ∘ (1) Dry-bulb temperatures ( C) 7.01 8.49 8480 1 ∘ ∗∗ (2) Dew-point temperatures ( C) −4.70 9.42 8480 .804 1 2 ∗∗ ∗∗ (3) Horizontal infrared radiation (Wh/m ) 520.51 249.65 8480 .379 .618 1 2 ∗∗ ∗∗ ∗∗ (4) Global horizontal radiation (Wh/m ) 287.98 208.35 8480 .228 −.082 −.294 1 2 ∗∗ ∗∗ ∗∗ ∗∗ (5) Direct normal radiation (Wh/m ) 271.47 253.63 8480 −.129 −.385 −.589 .753 1 2 ∗∗ ∗∗ ∗∗ ∗∗ ∗∗ (6) Difuse radiation (Wh/m ) 148.41 95.83 8480 .399 .189 .074 .735 .185 1 ∗∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed).

Table 3: Correlation of solar radiation and solar altitude. Pearson correlation Variables Mean Std.deviation � (1) (2) (3) 2 (1) Global horizontal radiation (Wh/m ) 275.29 228.63 17692 1 ∗∗ (2) GHR/HER (%) 38.54 20.65 17687 .776 1 ∘ ∗∗ ∗∗ (3) Solar altitude ( ) .36 37.17 35040 .680 .229 1 ∗∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed). incident of the direct solar rays. As such, the correlation between solar altitude and direct solar radiation should be 1200.0 positive and strong. In this section, however, we attempt to show the correlation between solar altitude and global 1000.0 horizontal radiation: the sum of global direct radiation and global difuse radiation. Te latter is afected by the presence 800.0 of clouds and other atmospheric particles. Figure 29 is a graph showing the dispersion of global horizontal radiation 600.0 in relation to solar altitude. By the result of 2011–2014 hourly data analysis, there was no correlation as shown in Figure 29. 400.0 �= y = 57.34 + 7∗x

Tisisbecausetherearemanynumbersofassayvalue( radiation Global horizontal 17 687 , ), which obstructs feld of vision. However, through 200.0 statistical analysis, the coefcient of determination was found �2 = 0.463 to be . Tis means that the independent variable .0 explains 46.3% of the dependent variable, thus indicating an −20 0 20406080 extremely high correlation. Solar altitude Te results obtained through the analysis of correlations between total solar irradiation in 2011–2014, GHR/EHR, and Figure 29: Scatter diagram showing the relationship between global solar altitude indicate a strong correlation between total solar horizontal radiation and solar altitude. irradiation and solar altitude to be � = 0.68,whichmeans being highly correlated. However, the correlation between GHR/EHR and solar altitude is � = 0.229.Tiscould data then assayed the relationship between sky cover and mean that the relation between total solar irradiation and solar radiation. Te calculated cloud cover (cloudiness) data GHR/EHRisnotstrongorthatthereisanothervariable shows 10-tenths data, which signifes less subdivisions as afecting the relationship of the two variables. Tere are compared to other data. It also becomes difcult to optically several reasons why the results presented in this chapter distinguish the relation because the number of data related to might not have ofered accurate explanations to the questions dispersion in Figure 30 is greatly large. However, the result of the subject matter. For instance, it could be due to the value was lower than the predicted value, considering the efect of other factors that are not considered by the study. closerelationofskycoverandsolarradiation.Assuch,it As such, determining other factors that are likely to afect can be assumed that there are other factors that afect solar solar radiation is of paramount importance. Table 3 shows the radiation besides clouds. analysis of correlation of solar radiation and solar altitude. Figure 30 indicates that the ratio of global horizontal radiation to extraterrestrial horizontal radiation has a neg- 3.2.3. Statistical Correlation between Solar Radiation and Sky ative correlation as the sky cover increases. Tis happens Cover. In Figure 30, the analysis was carried out by setting when discrete missing data of global horizontal radiation is 0. up the 0 point global horizontal radiation as discrete missing Notably, the correlation with GHR/EHR was � = −0.573 and 18 Advances in Meteorology

Table 4: Correlation of solar radiation and sky cover.

Pearson correlation Variables Mean Std.deviation � (1) (2) (3) (4) (5) (6) (1) Total sky cover 4.81 3.93 35040 1 2 ∗∗ (2) Horizontal infrared radiation (Wh/m ) 638.20 318.79 35040 .928 1 2 ∗∗ ∗∗ (3) Global horizontal radiation (Wh/m ) 275.29 228.63 17692 −.319 −.225 1 2 ∗∗ ∗∗ ∗∗ (4) Direct normal radiation (Wh/m ) 101.57 192.08 35040 −.316 −.282 .727 1 2 ∗∗ ∗∗ ∗∗ ∗∗ (5) Difuse radiation (Wh/m ) 81.29 116.99 35040 .024 .119 .810 .516 1 ∗∗ ∗∗ ∗∗ ∗∗ ∗∗ (6) GHR/HER (%) 38.54 20.65 17687 −.583 −.542 .807 .870 .570 1 ∗∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed).

2 R Linear = 0.377 � − 100 an -value of 0.45. Previously, the correlation coefcient betweenskycoverandsolarradiationwasnotover0.5,which is an indicator of a possible existence of other strong variables. 80 Afer a thorough analysis of the obtained data, AOD could also be classifed as a strong attenuation factor. As precipitable 60 water is related to the amount of clouds, the correlation between precipitable waters and horizontal infrared radiation is higher than 0.444. Table 5 shows the analysis of correlation 40 y = 55.17 − 3.49 ∗ x GHR/EHR of solar radiation and AOD. 20 3.2.5. Statistical Correlation between AOD (Aerosol Optical Depth) and Aerosols. Table6istheresultoftheanalysison 0 the correlation between AOD and airborne dust in all sky 0 246810 conditions for four years. Te correlation of each unit is over Total sky cover 0.7. Te results of SO2,NO2,PM-10,CO,andO3 with AOD showed no correlation. Te absolute value was not higher Figure 30: Scatter diagram showing the relationship between than 0.1. Tis is expected due to the infuence of AOD on GHR/EHR and total sky cover. analyzed airborne dust data such as sky cover, humidity, and also outer atmosphere data such as PM-10, CO2,andO3. was � = −0.319 with global horizontal radiation, which means 4. Conclusion that the sky cover with GHR/EHR is more visibly correlated than the one with only global horizontal radiation. Descriptive analysis of monthly average and frequency of Unlike the results obtained with solar radiation, horizon- weather elements was conducted. 35,040 hourly weather tal infrared radiation and sky cover had a positive correlation datasets belonging to Seoul city for a time period of 2011 to of � = 0.928, which is closer to 1. Tis means that sky cover 2014 were utilized for the study. Tis data was obtained from has a large infuence on the horizontal infrared radiation. KMA measured data as well as data calculated by equations, Table 4 shows the analysis of correlation of solar radiation and while the data describing the AOD and precipitable water sky cover. wereobtainedfromtheAERONETsystem.Teobtaineddata is an accurate depiction of Seoul’s climatic conditions. 3.2.4. Statistical Correlation between Solar Radiation and AOD Asshownthroughtheobtainedresults,althoughextrater- (Aerosol Optical Depth). In case of hourly total sky cover restrial direct radiation is the lowest in summer, dry-bulb values from 0 to 2 in the period 2011–2014, Table 5 shows temperature is the highest in summer. Also, the horizontal the correlation of AOD, global horizontal radiation, and infrared radiation follows a similar tendency to that shown GHR/EHR values from July to September. by the dry-bulb temperature. Te reason for considering only 0, 1, and 2 of total sky Teoretically, solar radiation in summer is expected to be cover (value) is that the results were only analyzed for the higher than that of other seasons. However, the actual calcu- purpose of eliminating factors which could have an efect on latedvalueisquitelow.Tismightbeduetotheattenuationof attenuation between two variables, and then the results were total sky cover and other atmospheric elements. Nevertheless, assayedinclearskywhenanalyzingcorrelationbetweenAOD this provides further proof that outdoor temperature cannot and solar radiation. be merely explained by the solar radiation factor alone. Analysis shows that AOD has negative correlations with InthecaseofAOD,thevaluesforJuneandJulywere the majority of the variables related to solar radiation, relatively high and showed a varying tendency to that of especially, the correlation between AOD and direct solar aerosols. Tis is because there is a high amount of precipitable radiation which indicated an �-value of −0.442 as well as the water in the atmosphere, in June, July, and August as it is correlation between AOD and GHR/EHR which indicated a rainy season and typhoon season in South Korea. Also, Advances in Meteorology 19

Table 5: Correlation of solar radiation and AOD (aerosol optical depth).

Pearson correlation Variables Mean Std.deviation � (1) (2) (3) (4) (5) (6) (7) (1) AOD .43 .33 104 1 ∗∗ (2) Precipitable water (cm) 2.39 .86 104 .405 1 ∗∗ (3) GHR/HER (%) 49.96 16.94 634 −.422 .094 1 2 ∗∗ (4) Horizontal infrared radiation (Wh/m ) 426.59 82.04 634 .018 .444 .066 1 2 ∗∗ ∗ ∗∗ ∗∗ (5) Global horizontal radiation (Wh/m ) 357.63 260.04 634 −.271 .200 .845 .227 1 2 ∗∗ ∗∗ ∗∗ (6) Direct normal radiation (Wh/m ) 333.69 237.60 634 −.450 .074 .920 −.007 .795 1 2 ∗ ∗∗ ∗∗ ∗∗ ∗∗ (7) Difuse radiation (Wh/m ) 159.96 107.02 634 −.069 .228 .571 .358 .807 .369 1 ∗∗ ∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed).

Table 6: Correlation of AOD and aerosols. Pearson correlation Variables Mean Std.deviation � (1) (2) (3) (4) (5) (6)

(1) SO2 (ppm) 10.32 101.02 35039 1 3 ∗∗ (2) PM-10 (�g/m ) 30.53 119.70 35039 .757 1 ∗∗ ∗∗ (3) O3 (ppm) 12.04 109.10 35039 .922 .698 1 ∗∗ ∗∗ ∗∗ (4) NO2 (ppm) 17.41 130.88 35039 .764 .593 .705 1 ∗∗ ∗∗ ∗∗ ∗∗ (5) CO (ppm) 11.18 107.49 35039 .936 .712 .865 .761 1 ∗∗ ∗ (6) AOD .65 .61 8138 .006 .076 .006 −.022 .009 1 ∗∗ ∗ Correlation is signifcant at the 0.01 level (2-tailed). Correlation is signifcant at the 0.05 level (2-tailed). solar radiation has an inverse relationship with sky cover, References precipitable water, and AOD. According to the analysis of each relation, global horizontal radiation was the lowest in [1] L. DR International, L. D & R International, 2010 Build- summer. ings Energy Data Book. U.S. Department of Energy, Mar. 2010, tables 1.1.3, 3.1.1. http://buildingsdatabook.eren.doe.gov/ In results of statistical correlation, the relationship values docs%5CDataBooks%5C2010BEDB.pdf. between variables of weather data were analyzed and con- [2] Markus, Tomas Andrew, and Edwin N. Morris. Buildings, verted into correlation coefcient. Te relationship between climate, and energy. Pitman Pub., 1980. outdoor temperature and solar radiation is usually assumed [3]J.A.DufeandW.A.Beckman,Solar Engineering of Termal to be almost of a linear nature. However, according to the Processes, vol. 3, Wiley, New York, NY, USA, 1980. calculated values, the interdependence of the two variables is [4] E. Aguado and J. E. Burt, Understanding Weather and Climate, not that directly proportional. Tis is because elements such Pearson Prentice Hall, Upper Saddle River, NJ, USA, 2007. as AOD, sky cover, and time lag were not considered in the [5] A. Tsangrassoulis, Short-Wave Radiation, James and James Ltd., frst instance. London, UK, 2001. In addition, the higher the solar altitude, the higher the [6]T.B.McKeeandS.K.Cox,“Scatteringofvisibleradiationby levels of solar radiation; however, a correlation between these � fnite clouds,” Journal of the Atmospheric Sciences,vol.31,no.7, 2 variables indicates a relatively low -value. Te results pp. 1885–1892, 1974. are then proof of the existence of other outer interventions [7] D. B. Crawley et al., “Energy plus: energy simulation program,” caused by weather conditions. ASHRAE Journal, pp. 49–56, 2000. � Te -value obtained from matching global horizontal [8]Handbook-Fundamentals,A.S.H.R.A.E.“Americansociety radiation to GHR/EHR was shown to be quite low. On the of heating, refrigerating and air-conditioning engineers.” Inc., � other hand, the -value shown by the relationship between NE Atlanta, GA 30329 (2009). direct radiation and GHR/EHR is too high. Evidently, accord- [9]I.L.Alboteanu,C.A.Bulucea,andS.Degeratu,“Estimating ing to the results, sky conditions are a contributing factor to solar irradiation absorbed by photovoltaic panels with low the relationship between GHR/EHR and direct radiation. concentration located in Craiova, Romania,” Sustainability,vol. As such, even though matching solar radiation and 7,no.3,pp.2644–2661,2015. AOD produce a negative correlation coefcient, each of the [10] D. Tevenard and C. A. Gueymard, “Updating the ASHRAE variables was not able to individually explain the levels of climatic data for design and standards,” in Proceedings of the solar radiation. 2010 ASHRAE Annual Conference, pp. 444–458, June 2009. [11] Te Globe Program (2002). Aerosols Protocol. http://globe.gov/ Conflicts of Interest sda/tg00/aerosol.pdf. [12] D. Tevenard and C. A. Gueymard, “Updating the ASHRAE Te authors declare no conficts of interest as far as this climatic data for design and standards,” in Proceedings of the manuscript is concerned. 2010 ASHRAE Annual Conference, pp. 444–458, June 2010. 20 Advances in Meteorology

[13] NASA EARTH OBSERVATORY, http://earthobservatory.nasa .gov. [14] Annual report of air quality in Korea in 2014 from Min- istry of Environment and National Institute of Environmental Research. http://www.me.go.kr/home/web/main.do. International Journal of Advances in The Scientifc Advances in Chemistry Scientica Geophysics World Journal Public Health Hindawi Hindawi Hindawi Hindawi Publishing Corporation Hindawi www.hindawi.com Volume 2018 www.hindawi.com Volume 2018 www.hindawi.com Volume 2018 http://www.hindawi.comwww.hindawi.com Volume 20182013 www.hindawi.com Volume 2018

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