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The effects of emission sources and meteorological factors on sulphur dioxide concentration of Great Isfahan, Iran
Atmospheric Environment 100 (2015) 94e101
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
The effects of emission sources and meteorological factors on sulphur dioxide concentration of Great Isfahan, Iran Fahimeh Hosseiniebalam*, Omid Ghaffarpasand Physics Department, University of Isfahan, Isfahan 81746, Iran
h i g h l i g h t s The air pollution problem in Isfahan has not enough investigated before. Industries and power generation plant around the city have considerable effects on SO2 concentration variation. Long term wind pattern of Isfahan is another important reason of high SO2 concentration. Meteorological factors have considerable effect on SO2 concentration variation. Temperature has largest effect on the SO2 concentration in Isfahan among the other factors.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 June 2014 Received in revised form 23 September 2014 Accepted 10 October 2014 Available online 30 October 2014
The great Isfahan has experienced an almost fast industrialization during the last years. The different factories and industries near that, cause one of the important environmental problems, air pollution, which has not enough investigated before in this area. The hourly, diurnal and seasonal variations of SO2 concentration as one of the most dangerous air pollutants, are studied to clarify the rule of industry on the air pollution problem. The data had been measured continuously from April 2006 to March 2007 at two stations, Lale & Azadi. The air pollution concentrations in an urban area have a close relationship with meteorological factors. Hence, the variation of SO2 concentration is analysed respect to the meteorological factors such as temperature, relative humidity, wind speed, solar radiation, and pressure. Moreover, the studied air pollutant is also statistically investigated through correlation analysis and stepwise multiple linear regression equation. It was observed that electric power plant near the Isfahan, Montazeri, has significant effects on the SO2 concentration in the east and north of Isfahan. Long-term pattern of Isfahan winds which is westerly during the winter and spring, and easterly during the summer and autumn, was recognized as one of another important factors influenced the SO2 concentration variations. It is also achieved that meteorological factors have considerable contribution, R2 ¼ 52%, on the SO2 concentration variation and temperature has largest effect among the others. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Air pollution Sulphur dioxide Isfahan Meteorological factors Statistical analysis
1. Introduction Air pollution and its dangerous impacts on the human health is one of the major problems of humanity caused mainly by industrialization and new styles of human life (Henschel et al., 2012; Melkonyan and Kuttler, 2012; Banerjee et al., 2011; Rodriguez et al., 2010). Population growth during the last century increased the number of automobiles in one hand and expand the industrial plants around the cities in the other hand. Both of them are the
* Corresponding author. E-mail address: [email protected] (F. Hosseiniebalam). http://dx.doi.org/10.1016/j.atmosenv.2014.10.012 1352-2310/© 2014 Elsevier Ltd. All rights reserved.
important sources introduced a huge amount of air pollutants to the lower atmosphere. Moreover, increasing the energy demand and further developing the power generation plants using fossil fuels is also another origin which emitted dangerous pollutants such as sulphuric dioxide (SO2) in the atmosphere (Zhao et al., 2009). SO2 concentration in the lower atmosphere has more interested among the other air pollutants during the last years (Nazari et al., 2012; Iqbal et al., 2014). SO2 is known as one of the indicators of air quality (Jeong and Park, 2013). The main source of SO2 in the urban areas is burning the fossil fuels such as coal and heavy fuel oil (73%), other industrial facilities (20%), and natural sources (less than 7%) (Nazari et al., 2012). SO2 among the other air pollutants has worse effects on the human health and environment
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
(Luvsan et al., 2012). SO2 can react with the other atmospheric chemical compounds to form small particles. These particles penetrate deeply into the respiratory system and cause respiratory disease and sometimes respiratory cancers (EPA, 2011). On the other hand, SO2 can form an acidic solution in water by certain reactions given by (Akabueze et al., 2012):
95
characteristics of climate and weather condition of Isfahan are illustrated firstly, then the effective factors on SO2 concentration level is introduced and discussed. 2. Materials and methods 2.1. Features of Isfahan
1 SO2 þ O2 /SO3 2
(1)
SO3 þ H2 O/H2 SO4
(2)
Hence, SO2 is a major component of acid rain which damage a lot the environment. The concentration of SO2 in an urban area can be consider as a symbol of the effects of industrialization on the environment (Zhao et al., 2009; Luvsan et al., 2012). Thus, study of SO2 level in an area, offers important opportunity for tracing environmental destruction caused by industrialization (Flemming et al., 2005). However, there are many effective factors on the SO2 concentration of a region which were studied by many previous investigators (Chu et al., 2008; Iqbal et al., 2014). It was shown that meteorological factors affect the SO2 concentration depend on the climate conditions of the study area (Khedairia and Khadir, 2012; Henschel et al., 2014; Ray and Kim, 2014). Although there are many studies in different place of world which investigated the SO2 concentration variation and its effective factors, but there are still some new places experienced an almost fast industrialization recently and was not considered, up to now. The great Isfahan, shown in Fig. 1, is one of those new places. The historical city of Isfahan, in the center of middle east was recognized as the second most polluted city of Iran, after Tehran. Nowadays, the air pollution has became one of major problems of this city, but there is no any studies which were investigated the SO2 concentration level and its effective factors in this area. On the other hand, a lot of industrial factories near the Isfahan with distance less than 50 km obtain an almost unique opportunity to study the effect of industry on the environment. The purpose of this paper is to study SO2 concentration pattern and the effects of industrial emission sources, meteorological factors, climate and geographic conditions on the SO2 concentration variation during a year in the great Isfahan. For this, the
The historical city of Isfahan, located in the center of the Iran plateau surrounded by the largest and most arid desert land of Iran. The outstanding features of Isfahan are little rainfall, average less than 122.7 mm, and fast winds. Isfahan is located in 33.38 N, 51.39 W, and elevation 1550e1650 m, with more than 2.1 million population. There are more than a million automotive and heavyduty vehicles using diesels, gasoline, and natural gas in Isfahan. This city is known as the largest industrialized region in Iran, where there are many industrial states, steel companies, and etc. in its suburb with distances less than 50 km indicated in Fig. 2. There is also one of the biggest electric power plant of Iran, Montazeri, in the suburb of Isfahan, which generate around 10.735 GWh electric energy during the 2007 (Nazari et al., 2012). Montazeri plant is a steam power plant which is recently use natural gas. However, Montazeri use heavy oil during the cold days due to increasing the domestic heating (Nazari et al., 2012). Regarding the fact that Irans steam power plants do not utilize SO2 reduction system, a considerable amount of this pollutants is produced in those plants which lead to increase the SO2 concentration level (Nazari et al., 2012). On the other hand, there is a sugar factory in the east of Isfahan city indicated in Fig. 2(a) by arrow E, which can be consider as another source of air pollutants. 2.2. Measurement stations The hourly SO2 concentration data is attained from April 2006 to March 2007 by the Environmental Department of Isfahan. The sampling sites which are located in the Lale and Azadi squares, indicated in Fig. 2, are respectively the northern and southern gates of the town, and named Lale and Azadi station hereinafter. It should be noted that those squares are characterized by a high traffic density as well as the population concentrated. The meteorological factors, i.e. atmospheric pressure, P (hpa), air temperature, T ( C),
Fig. 1. Map of Iran including the great Isfahan.
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F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
Fig. 2. (a) Image map of Isfahan including the sampling stations (unnamed arrows), and main industries. The arrow named B and C are the biggest steel companies of Iran named Mobarakeh steel company and Zob Ahan respectively, arrow named D is one of the biggest power generation plant of Iran, and arrow named E is a sugar factory (Google Map and Google earth imagery (Google Inc.)). (b) The position of sampling sites.
relative humidity, RH (%), wind speed, WS (m/s), sunshine hours, SS, and solar radiation, RAD (W m2) are continuously measured by the Meteorological Organization of Islamic Republic of Iran. The meteorological stations are situated distances less than 10 km away from the air pollution sampling sites.
3. Results and discussion 3.1. Hourly variation of SO2 concentration The averaged hourly variation of SO2 concentration at sampling stations is shown in Fig. 3. It was seen that Lale station had measured higher averaged concentration of SO2 compared to the Azadi station. This is due to the Montazeri power plant in the near of the Lale station. The rule of Montazeri power plant will be
Fig. 3. Hourly variations of SO2 concentration during April 2006 to March 2007.
further clarified in the next section. However, the pattern of SO2 concentration in the two monitored stations has noticeable difference which come from different traffic style of studied stations. Lale station is one of the main gate of the town and there are many industrial plant and factories near that. Hence, rush hours at this station is around 6:00 he9:00 h, when most of the people were going to their job. Thus, traffic density and public transportation volume especially vehicles based on gasoline and natural gas increased during the rush hours and so SO2 concentration increases. On the other hand, many of administrative centers of Isfahan are concentrated around the Azadi station. Hence, the rush hours of this station is around 10:00 he14:00 h when the administrative authorities and so SO2 concentration increases. Isfahan is in the middle of an arid land and has almost warm afternoons. SO2 concentration reduction during the afternoons can be due to increase of the mixing layer height. On the other hand, SO2 concentration also increases during the night at the both stations. Two reasons can be provide for this fact. First, formation the nocturnal stable boundary layer during the night which decreases the air mixing layer and increasing the SO2 concentration. Second, both stations experienced a considerable transit of gasoline vehicles, especially Lale, at the late night. The variations suggest that traffic and heating related combustion sources are driving the hourly pattern. This bi-model is similar to those reported by Zhao et al. (2009) in Beijing, China, Makara et al. (2010) in Hungary (Szeged) and Germany (Freiburg), and Henschel et al. (2014) in 6 European cities including Athens, Barcelona, Brussels, London, Paris, and Vienna. The noticeable difference of data measured between two stations in Isfahan is in contrast with the others. It is observed that the maximum concentration of SO2 in the Lale station (~65 ppb x 180 mg/m3) is significantly larger than maximum concentration value of SO2 in six European cities (x95 mg/m3)
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
Fig. 4. The diurnal variation of SO2 level at (a) both stations, (b) Lale station, and (c) (b) Azadi station during April 2006 to March 2007.
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F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
Fig. 5. Monthly variations of SO2 concentration during April 2006 to March 2007.
illustrated in the study of Henschel et al. (2013). This can be due to the near city industries which do not utilize reduction systems in one hand, and a lot of old cars in traffic in the city which do not use catalytic converter or their converters were destroyed in the other hand. 3.2. Diurnal variation of SO2 concentration The averaged diurnal variation of SO2 concentration during a week presented in Fig. 4. First, it should be noted that Fridays and Thursdays are the weekends in Iran. It is obvious that Lale has considerable larger SO2 concentration respect to the Azadi station (Fig. 4(a)). It was observed before and will be discussed later. However, SO2 concentration at both stations reaches to its minimum values at Fridays and Thursdays when the traffic density decreases a lot. This was called “weekend effect” by Atkinson-Palombo et al. (2006). The mid-week days had experienced highest level of SO2 concentration.
two stations during the cold days. This fact can be due to the long term pattern of Isfahan winds in one hand, and different factories in the suburb of Isfahan in the other hand. The long term wind rose of Isfahan during the April, May, and June is graphed in Fig. 6(a). The prevailing winds of Isfahan during these months are southwesterly and westerly. On the other hand, the biggest steel companies of Iran, Zob Ahan and Mobarakeh steel company are in the southwest and south of Isfahan, indicated by B and C arrows respectively in Fig. 2(a), with distances less than 40 km respect to the Azadi station. Mobarakeh steel company used electric arc furnace in steel production, while Zob Ahan used petroleum coke. Hence, Mobarakeh steel company has a minor role in pollutant propagation. The larger concentration of SO2 measured by Azadi station during the warm days may be due to the western steel company of Isfahan, Zob Ahan, in one hand and prevailing western and southwestern winds of Isfahn in that time in the other hand. As it was mentioned before, one of the biggest electrical power plant of Iran, Montazeri, is in the north west of Isfahan. This steam power plant have used natural gas recently and so has minor effects on the SO2 concentration during the usual days of the year especially warm days. During the cold days of the year, domestic heating was increased a lot and power plant had been forced to use heavy fuel oil to generate the electricity. This cause to release a large amount of SO2 in a distances less than 40 km respect to the Lale station. On the other hand, six months pattern of Isfahan winds during JulyeDecember shows that the dominant winds of Isfahan change to easterly, southeasterly and northeasterly, presented in Fig. 6(b). The pattern of Isfahan winds during this time cause that eastern sugar factory of Isfahn, indicated by arrow E in Fig. 2(a), became one of major emission sources of SO2, while it reduces the effects of western steel company on the Azadi station. 3.4. Correlation analysis
3.3. Monthly variation of SO2 concentration The averaged monthly variations of SO2 concentration during the studied year is shown in Fig. 5. It is observed that Azadi station during the warm days of the year measured slightly higher SO2 concentration, while there is a considerable difference between SO2 concentration monitored at
The Pearson correlation coefficients of SO2 concentration respect to meteorological parameters are illustrated in Table 1. It is observed that SO2 concentration is positively correlated by relative humidity and pressure, while the opposite is achieved for temperature, sunshine hours, solar radiation and wind speed. The atmospheric mixing layer height is increased by increasing the
Fig. 6. Long term pattern of wind direction in Isfahan at (a) April, May, and June, and (b) July to December.
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101 Table 1 Correlation coefficients of SO2 concentration respect to meteorological factors in studied stations.
Azadi Lale
RH
T
WS
WD
RAD
P
SS
0.4 0.52
0.48 0.67
0.13 0.18
0.14 0.23
0.33 0.38
0.31 0.45
0.35 0.47
temperature. Both of the amount of solar radiation and the number of sunshine hours have the same rule as the temperature. Hence, those are negatively correlated by SO2 concentration at the both stations. However, the monthly variation of SO2 concentration at both station respect to the mean temperature are compared in Fig. 7(a). It is obvious that SO2 concentration decreases when atmospheric temperature and so atmospheric mixing layer height increases. The positive correlation between SO2 concentration and pressure confirmed in Fig. 7(b). SO2 concentration decreases with decreasing the pressure. Isfahan is affected by anticyclone systems in winter time cause usually long time thermal inversions, more than two days, which result in increase SO2 concentration. Wind speed has a clarified rule on the air pollution concentration. Increasing the wind speed causes to increase the dispersion and propagation of air pollutants in low atmosphere and so reduce air pollution local concentrations. The negative correlation of SO2 concentration and wind speed can be observed in Fig. 7(c), where the variations of SO2 concentration and wind speed are compared. The positive correlation of SO2 concentration and relative humidity is also observed in Fig. 7(d).
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3.5. Regression analysis In this study, we used regression analysis to provide a preliminary knowledge of the relationship between meteorological factors and SO2 concentration. For this, the step-wise multiple regression analysis is implemented where meteorological factors and SO2 concentration are assumed independent and dependent variables, respectively (Pudasainee et al., 2006; Celik and Kadi, 2007; Banarjee et al., 2011). The regression analysis was implemented just for Azadi station. The constructed regression equation is expressed as:
CSO2 ¼ 1673 6:35T þ 0:671RH þ 2:05P 1:94WS R2 ¼ 52%
(3)
The proposed equation illustrated that ambient SO2 concentration in Azadi station is dependent on temperature, relative humidity, pressure and wind speed. The meteorological factors are cumulatively responsible for 52% of SO2 concentration and remaining were independent of meteorological factors. The effects of meteorological factors is more clarified in Fig. 8, where the annual concentration of SO2 as a function of meteorological factors are presented. Moreover, mathematical functions illustrating dependencies of SO2 concentration with each meteorological factor are illustrated in Table 2. It should be noted that the most recommended equations were chosen based on the maximum values of determination coefficients. All the investigated equations were significant at the 1% error level. Partial correlation coefficients among all the independent variables signify that contribution of temperature is the most significant meteorological
Fig. 7. Monthly variations of SO2 concentration at both stations during April 2006 to March 2007 respect to averaged (a) temperature, (b) pressure, (c) wind speed, and (d) relative humidity.
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F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
Fig. 8. Regression plots of SO2 concentration during April 2006 to March 2007 respect to averaged (a) temperature, (b) pressure, (c) wind speed, and (d) relative humidity.
factor causing variation of ambient SO2 concentration. Pressure is the next meteorological factor has the largest contribution on the SO2 concentration variation.
4. Conclusions In this study, the hourly, diurnal, and monthly variations of SO2 concentration during April 2006 to March 2007 were investigated to clarify the affective factors. It was observed that SO2 concentration reach to its maximum value at the mornings during the rush hours, while it reaches to its minimum value at the afternoons when the height of atmospheric mixing layer increases by increasing the temperature. The peak observed during the nights is due to the formation of nocturnal stable boundary and transit of heavy gasoline vehicles around the studied stations. However, a bimodel including traffic and heating related combustion sources is recognized as the main reason which derived the hourly pattern. The weekend effect was also observed in great Isfahan, when SO2 concentration decreases due to decrease the traffic density at the weekends. Furthermore, the industrial around the Isfahn, especially western steel company and power plant, were recognized as the main artificial sources which driving the monthly pattern of SO2 concentration respect to the long term pattern of Isfahan winds. Correlation analysis in addition to a step-wise multiple regression analysis were also implemented to study the effects of meteorological factors quantitatively. It was observed that SO2 concentration is negatively correlated by temperature, sunshine hours, solar radiation, and wind speed, while the opposite was achieved for relative humidity and pressure. Moreover, the
Table 2 Results of regression analysis and equations between SO2 concentration and meteorological factors. Meteorological factor
Equation
R2 (%)
Temperature Wind speed Relative humidity Pressure
102 7.57T 114 2.82WS 9.05 þ 1.24RH 3771 þ 4.53P
23.472 7.904 8.103 13.764
meteorological factors have considerable contribution on the SO2 concentration variations, R2 ¼ 52%. Finally, it was observed that ambient concentration of SO2 in the great Isfahan is in thinkable condition and industries around the city have a considerable effect on that. Hence, it would suggest that all of the Isfahan industries force to utilize SO2 reduction systems. Moreover, seasonal inspections on the cars catalytic converters would be another way to decrease the SO2 concentration level. References Akabueze, C.I., Tsafe, A.I., Itodo, A.U., Uba, A., 2012. Influence of climate and height on the levels of sulfur dioxide (SO2) in Sokoto high traffic density and near atmospheric region. World Environ. 2, 51e55. Atkinson-Palombo, Miller, J.A., Balling Jr., R.C., 2006. Quantifying the ozone “weekend effect” at various locations in Phoenix, Arizona. Atmos. Environ. 40, 7644e7658. Banerjee, T., Singh, S.B., Srivastava, R.K., 2011. Development and performance of statistical models correlating air pollutants and meteorological variables at Pantnagar, India. Atmos. Res. 99, 505e517. Celik, M.B., Kadi, I., 2007. The relation between meteorological factors and pollutants concentrations in Karabük City. G. U. J. Sci. 20, 87e95. Chu, P.C., Chen, Y., Lu, S., 2008. Atmospheric effects on winter SO2 pollution in Lanzhou, China. Atmos. Res. 89, 365e373. EPA, 2011. Six Common Air Pollutants, Sulphur Dioxide. USA. Available via. http:// www.epa.gov/oaqps001/sulphur dioxide/health.html. Flemming, J., Stern, R., Yamartino, R.J., 2005. A new air quality regime classification scheme for O3, NO2, SO2 and PM10 observation sites. Atmos. Environ. 39, 6121e6129. Henschel, S., Atkinson, Zeka, A., Le Tertre, A., Analitis, A., Katsouyanni, K., Chanel, O., Pascal, M., Forsberg, B., Medina, S., Goodman, P.G., 2012. Air pollution interventions and their impact on public health. Int. J. Public Health 57, 757e768. Henschel, S., Queral, X., Atkinson, R., Pandolfi, M., Zeka, A., Le Tertre, A., Analitis, A., Katsouyanni, K., Chanel, O., Pascal, M., Bouland, C., Haluza, D., Medina, S., Goodman, P.G., 2014. Ambient air SO2 patterns in 6 European cities. Atmos. Environ. 79, 236e247. Iqbal, M.A., Kim, K.H., Shon, Z.H., Sohn, J.R., Jeon, E.C., Kim, Y.S., Oh, J.M., 2014. Comparison of ozone pollution levels at various sites in Seoul, a megacity in Northeast Asia. Atmos. Res. 138, 330e345. Jeong, J.I., Park, R.J., 2013. Effects of the meteorological variability on regional air quality in East Asia. Atmos. Environ. 69, 46e55. Khedairia, S., Khadir, M.T., 2012. Impact of clustered meteorological parameters on air pollutants concentrations in the region of Annaba, Algeria. Atmos. Res. 113, 89e101. Luvsan, M.E., Shie, R.H., Purevdori, T., Badarch, L., Baldorj, B., Chan, C.C., 2012. The influence of emission sources and meteorological conditions on SO2 pollution in Mongolia. Atmos. Environ. 61, 542e549. Makara, L., Mayer, H., Mika, J., Santa, T., Holst, J., 2010. Variations of traffic related air pollution on different time scales in Szeged, Hungary, and Freiburg, Germany. Phys. Chem. Earth Part A/B/C 35, 85e94.
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101 Melkonyan, A., Kuttler, W., 2012. Long-term analysis of NO, NO2, and O3 concentrations in North Rhine-Westphalia. Atmos. Environ. 60, 316e326. Nazari, S., Shahhosseini, O., Sohrabi-Kashani, A., Davari, S., Sahabi, H., Rezaeian, A., 2012. SO2 pollution of heavy oil-fired steam power plants in Iran. Energy Policy 43, 456e465. Pudasainee, D., Sapkota, B., Shrestha, M.L., Kaga, A., Kondo, A., Inouo, Y., 2006. Ground level ozone concentrations and its association with NOx and meteorological parameters in Kathmandu valley, Nepal. Atmos. Environ. 40, 8081e8087.
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Ray, Sh, Kim, Ki-H., 2014. The pollution status of sulphur dioxide in major urban areas of Korean between 1989-2010. Atmos. Res. http://dx.doi.org/10.1016/ j.atmosres. 2014.05.011. Rodriguez, C.A.M., da Rocha, R.P., Bombardi, R., 2010. On the development of ~o Paulo: mean meteorological characsummer thunderstorms in the city of Sa teristics and pollution effect. Atmos. Res. 96, 477e488. Zhao, X., Xu, X., Xu, J., Meng, W., Pu, W., 2009. Seasonal and diurnal variations of ambient PM2.5 concentration in urban and rural environments in Beijing. Atmos. Environ. 43, 2893e2900.
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
The effects of emission sources and meteorological factors on sulphur dioxide concentration of Great Isfahan, Iran Fahimeh Hosseiniebalam*, Omid Ghaffarpasand Physics Department, University of Isfahan, Isfahan 81746, Iran
h i g h l i g h t s The air pollution problem in Isfahan has not enough investigated before. Industries and power generation plant around the city have considerable effects on SO2 concentration variation. Long term wind pattern of Isfahan is another important reason of high SO2 concentration. Meteorological factors have considerable effect on SO2 concentration variation. Temperature has largest effect on the SO2 concentration in Isfahan among the other factors.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 June 2014 Received in revised form 23 September 2014 Accepted 10 October 2014 Available online 30 October 2014
The great Isfahan has experienced an almost fast industrialization during the last years. The different factories and industries near that, cause one of the important environmental problems, air pollution, which has not enough investigated before in this area. The hourly, diurnal and seasonal variations of SO2 concentration as one of the most dangerous air pollutants, are studied to clarify the rule of industry on the air pollution problem. The data had been measured continuously from April 2006 to March 2007 at two stations, Lale & Azadi. The air pollution concentrations in an urban area have a close relationship with meteorological factors. Hence, the variation of SO2 concentration is analysed respect to the meteorological factors such as temperature, relative humidity, wind speed, solar radiation, and pressure. Moreover, the studied air pollutant is also statistically investigated through correlation analysis and stepwise multiple linear regression equation. It was observed that electric power plant near the Isfahan, Montazeri, has significant effects on the SO2 concentration in the east and north of Isfahan. Long-term pattern of Isfahan winds which is westerly during the winter and spring, and easterly during the summer and autumn, was recognized as one of another important factors influenced the SO2 concentration variations. It is also achieved that meteorological factors have considerable contribution, R2 ¼ 52%, on the SO2 concentration variation and temperature has largest effect among the others. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Air pollution Sulphur dioxide Isfahan Meteorological factors Statistical analysis
1. Introduction Air pollution and its dangerous impacts on the human health is one of the major problems of humanity caused mainly by industrialization and new styles of human life (Henschel et al., 2012; Melkonyan and Kuttler, 2012; Banerjee et al., 2011; Rodriguez et al., 2010). Population growth during the last century increased the number of automobiles in one hand and expand the industrial plants around the cities in the other hand. Both of them are the
* Corresponding author. E-mail address: [email protected] (F. Hosseiniebalam). http://dx.doi.org/10.1016/j.atmosenv.2014.10.012 1352-2310/© 2014 Elsevier Ltd. All rights reserved.
important sources introduced a huge amount of air pollutants to the lower atmosphere. Moreover, increasing the energy demand and further developing the power generation plants using fossil fuels is also another origin which emitted dangerous pollutants such as sulphuric dioxide (SO2) in the atmosphere (Zhao et al., 2009). SO2 concentration in the lower atmosphere has more interested among the other air pollutants during the last years (Nazari et al., 2012; Iqbal et al., 2014). SO2 is known as one of the indicators of air quality (Jeong and Park, 2013). The main source of SO2 in the urban areas is burning the fossil fuels such as coal and heavy fuel oil (73%), other industrial facilities (20%), and natural sources (less than 7%) (Nazari et al., 2012). SO2 among the other air pollutants has worse effects on the human health and environment
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
(Luvsan et al., 2012). SO2 can react with the other atmospheric chemical compounds to form small particles. These particles penetrate deeply into the respiratory system and cause respiratory disease and sometimes respiratory cancers (EPA, 2011). On the other hand, SO2 can form an acidic solution in water by certain reactions given by (Akabueze et al., 2012):
95
characteristics of climate and weather condition of Isfahan are illustrated firstly, then the effective factors on SO2 concentration level is introduced and discussed. 2. Materials and methods 2.1. Features of Isfahan
1 SO2 þ O2 /SO3 2
(1)
SO3 þ H2 O/H2 SO4
(2)
Hence, SO2 is a major component of acid rain which damage a lot the environment. The concentration of SO2 in an urban area can be consider as a symbol of the effects of industrialization on the environment (Zhao et al., 2009; Luvsan et al., 2012). Thus, study of SO2 level in an area, offers important opportunity for tracing environmental destruction caused by industrialization (Flemming et al., 2005). However, there are many effective factors on the SO2 concentration of a region which were studied by many previous investigators (Chu et al., 2008; Iqbal et al., 2014). It was shown that meteorological factors affect the SO2 concentration depend on the climate conditions of the study area (Khedairia and Khadir, 2012; Henschel et al., 2014; Ray and Kim, 2014). Although there are many studies in different place of world which investigated the SO2 concentration variation and its effective factors, but there are still some new places experienced an almost fast industrialization recently and was not considered, up to now. The great Isfahan, shown in Fig. 1, is one of those new places. The historical city of Isfahan, in the center of middle east was recognized as the second most polluted city of Iran, after Tehran. Nowadays, the air pollution has became one of major problems of this city, but there is no any studies which were investigated the SO2 concentration level and its effective factors in this area. On the other hand, a lot of industrial factories near the Isfahan with distance less than 50 km obtain an almost unique opportunity to study the effect of industry on the environment. The purpose of this paper is to study SO2 concentration pattern and the effects of industrial emission sources, meteorological factors, climate and geographic conditions on the SO2 concentration variation during a year in the great Isfahan. For this, the
The historical city of Isfahan, located in the center of the Iran plateau surrounded by the largest and most arid desert land of Iran. The outstanding features of Isfahan are little rainfall, average less than 122.7 mm, and fast winds. Isfahan is located in 33.38 N, 51.39 W, and elevation 1550e1650 m, with more than 2.1 million population. There are more than a million automotive and heavyduty vehicles using diesels, gasoline, and natural gas in Isfahan. This city is known as the largest industrialized region in Iran, where there are many industrial states, steel companies, and etc. in its suburb with distances less than 50 km indicated in Fig. 2. There is also one of the biggest electric power plant of Iran, Montazeri, in the suburb of Isfahan, which generate around 10.735 GWh electric energy during the 2007 (Nazari et al., 2012). Montazeri plant is a steam power plant which is recently use natural gas. However, Montazeri use heavy oil during the cold days due to increasing the domestic heating (Nazari et al., 2012). Regarding the fact that Irans steam power plants do not utilize SO2 reduction system, a considerable amount of this pollutants is produced in those plants which lead to increase the SO2 concentration level (Nazari et al., 2012). On the other hand, there is a sugar factory in the east of Isfahan city indicated in Fig. 2(a) by arrow E, which can be consider as another source of air pollutants. 2.2. Measurement stations The hourly SO2 concentration data is attained from April 2006 to March 2007 by the Environmental Department of Isfahan. The sampling sites which are located in the Lale and Azadi squares, indicated in Fig. 2, are respectively the northern and southern gates of the town, and named Lale and Azadi station hereinafter. It should be noted that those squares are characterized by a high traffic density as well as the population concentrated. The meteorological factors, i.e. atmospheric pressure, P (hpa), air temperature, T ( C),
Fig. 1. Map of Iran including the great Isfahan.
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Fig. 2. (a) Image map of Isfahan including the sampling stations (unnamed arrows), and main industries. The arrow named B and C are the biggest steel companies of Iran named Mobarakeh steel company and Zob Ahan respectively, arrow named D is one of the biggest power generation plant of Iran, and arrow named E is a sugar factory (Google Map and Google earth imagery (Google Inc.)). (b) The position of sampling sites.
relative humidity, RH (%), wind speed, WS (m/s), sunshine hours, SS, and solar radiation, RAD (W m2) are continuously measured by the Meteorological Organization of Islamic Republic of Iran. The meteorological stations are situated distances less than 10 km away from the air pollution sampling sites.
3. Results and discussion 3.1. Hourly variation of SO2 concentration The averaged hourly variation of SO2 concentration at sampling stations is shown in Fig. 3. It was seen that Lale station had measured higher averaged concentration of SO2 compared to the Azadi station. This is due to the Montazeri power plant in the near of the Lale station. The rule of Montazeri power plant will be
Fig. 3. Hourly variations of SO2 concentration during April 2006 to March 2007.
further clarified in the next section. However, the pattern of SO2 concentration in the two monitored stations has noticeable difference which come from different traffic style of studied stations. Lale station is one of the main gate of the town and there are many industrial plant and factories near that. Hence, rush hours at this station is around 6:00 he9:00 h, when most of the people were going to their job. Thus, traffic density and public transportation volume especially vehicles based on gasoline and natural gas increased during the rush hours and so SO2 concentration increases. On the other hand, many of administrative centers of Isfahan are concentrated around the Azadi station. Hence, the rush hours of this station is around 10:00 he14:00 h when the administrative authorities and so SO2 concentration increases. Isfahan is in the middle of an arid land and has almost warm afternoons. SO2 concentration reduction during the afternoons can be due to increase of the mixing layer height. On the other hand, SO2 concentration also increases during the night at the both stations. Two reasons can be provide for this fact. First, formation the nocturnal stable boundary layer during the night which decreases the air mixing layer and increasing the SO2 concentration. Second, both stations experienced a considerable transit of gasoline vehicles, especially Lale, at the late night. The variations suggest that traffic and heating related combustion sources are driving the hourly pattern. This bi-model is similar to those reported by Zhao et al. (2009) in Beijing, China, Makara et al. (2010) in Hungary (Szeged) and Germany (Freiburg), and Henschel et al. (2014) in 6 European cities including Athens, Barcelona, Brussels, London, Paris, and Vienna. The noticeable difference of data measured between two stations in Isfahan is in contrast with the others. It is observed that the maximum concentration of SO2 in the Lale station (~65 ppb x 180 mg/m3) is significantly larger than maximum concentration value of SO2 in six European cities (x95 mg/m3)
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101
Fig. 4. The diurnal variation of SO2 level at (a) both stations, (b) Lale station, and (c) (b) Azadi station during April 2006 to March 2007.
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Fig. 5. Monthly variations of SO2 concentration during April 2006 to March 2007.
illustrated in the study of Henschel et al. (2013). This can be due to the near city industries which do not utilize reduction systems in one hand, and a lot of old cars in traffic in the city which do not use catalytic converter or their converters were destroyed in the other hand. 3.2. Diurnal variation of SO2 concentration The averaged diurnal variation of SO2 concentration during a week presented in Fig. 4. First, it should be noted that Fridays and Thursdays are the weekends in Iran. It is obvious that Lale has considerable larger SO2 concentration respect to the Azadi station (Fig. 4(a)). It was observed before and will be discussed later. However, SO2 concentration at both stations reaches to its minimum values at Fridays and Thursdays when the traffic density decreases a lot. This was called “weekend effect” by Atkinson-Palombo et al. (2006). The mid-week days had experienced highest level of SO2 concentration.
two stations during the cold days. This fact can be due to the long term pattern of Isfahan winds in one hand, and different factories in the suburb of Isfahan in the other hand. The long term wind rose of Isfahan during the April, May, and June is graphed in Fig. 6(a). The prevailing winds of Isfahan during these months are southwesterly and westerly. On the other hand, the biggest steel companies of Iran, Zob Ahan and Mobarakeh steel company are in the southwest and south of Isfahan, indicated by B and C arrows respectively in Fig. 2(a), with distances less than 40 km respect to the Azadi station. Mobarakeh steel company used electric arc furnace in steel production, while Zob Ahan used petroleum coke. Hence, Mobarakeh steel company has a minor role in pollutant propagation. The larger concentration of SO2 measured by Azadi station during the warm days may be due to the western steel company of Isfahan, Zob Ahan, in one hand and prevailing western and southwestern winds of Isfahn in that time in the other hand. As it was mentioned before, one of the biggest electrical power plant of Iran, Montazeri, is in the north west of Isfahan. This steam power plant have used natural gas recently and so has minor effects on the SO2 concentration during the usual days of the year especially warm days. During the cold days of the year, domestic heating was increased a lot and power plant had been forced to use heavy fuel oil to generate the electricity. This cause to release a large amount of SO2 in a distances less than 40 km respect to the Lale station. On the other hand, six months pattern of Isfahan winds during JulyeDecember shows that the dominant winds of Isfahan change to easterly, southeasterly and northeasterly, presented in Fig. 6(b). The pattern of Isfahan winds during this time cause that eastern sugar factory of Isfahn, indicated by arrow E in Fig. 2(a), became one of major emission sources of SO2, while it reduces the effects of western steel company on the Azadi station. 3.4. Correlation analysis
3.3. Monthly variation of SO2 concentration The averaged monthly variations of SO2 concentration during the studied year is shown in Fig. 5. It is observed that Azadi station during the warm days of the year measured slightly higher SO2 concentration, while there is a considerable difference between SO2 concentration monitored at
The Pearson correlation coefficients of SO2 concentration respect to meteorological parameters are illustrated in Table 1. It is observed that SO2 concentration is positively correlated by relative humidity and pressure, while the opposite is achieved for temperature, sunshine hours, solar radiation and wind speed. The atmospheric mixing layer height is increased by increasing the
Fig. 6. Long term pattern of wind direction in Isfahan at (a) April, May, and June, and (b) July to December.
F. Hosseiniebalam, O. Ghaffarpasand / Atmospheric Environment 100 (2015) 94e101 Table 1 Correlation coefficients of SO2 concentration respect to meteorological factors in studied stations.
Azadi Lale
RH
T
WS
WD
RAD
P
SS
0.4 0.52
0.48 0.67
0.13 0.18
0.14 0.23
0.33 0.38
0.31 0.45
0.35 0.47
temperature. Both of the amount of solar radiation and the number of sunshine hours have the same rule as the temperature. Hence, those are negatively correlated by SO2 concentration at the both stations. However, the monthly variation of SO2 concentration at both station respect to the mean temperature are compared in Fig. 7(a). It is obvious that SO2 concentration decreases when atmospheric temperature and so atmospheric mixing layer height increases. The positive correlation between SO2 concentration and pressure confirmed in Fig. 7(b). SO2 concentration decreases with decreasing the pressure. Isfahan is affected by anticyclone systems in winter time cause usually long time thermal inversions, more than two days, which result in increase SO2 concentration. Wind speed has a clarified rule on the air pollution concentration. Increasing the wind speed causes to increase the dispersion and propagation of air pollutants in low atmosphere and so reduce air pollution local concentrations. The negative correlation of SO2 concentration and wind speed can be observed in Fig. 7(c), where the variations of SO2 concentration and wind speed are compared. The positive correlation of SO2 concentration and relative humidity is also observed in Fig. 7(d).
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3.5. Regression analysis In this study, we used regression analysis to provide a preliminary knowledge of the relationship between meteorological factors and SO2 concentration. For this, the step-wise multiple regression analysis is implemented where meteorological factors and SO2 concentration are assumed independent and dependent variables, respectively (Pudasainee et al., 2006; Celik and Kadi, 2007; Banarjee et al., 2011). The regression analysis was implemented just for Azadi station. The constructed regression equation is expressed as:
CSO2 ¼ 1673 6:35T þ 0:671RH þ 2:05P 1:94WS R2 ¼ 52%
(3)
The proposed equation illustrated that ambient SO2 concentration in Azadi station is dependent on temperature, relative humidity, pressure and wind speed. The meteorological factors are cumulatively responsible for 52% of SO2 concentration and remaining were independent of meteorological factors. The effects of meteorological factors is more clarified in Fig. 8, where the annual concentration of SO2 as a function of meteorological factors are presented. Moreover, mathematical functions illustrating dependencies of SO2 concentration with each meteorological factor are illustrated in Table 2. It should be noted that the most recommended equations were chosen based on the maximum values of determination coefficients. All the investigated equations were significant at the 1% error level. Partial correlation coefficients among all the independent variables signify that contribution of temperature is the most significant meteorological
Fig. 7. Monthly variations of SO2 concentration at both stations during April 2006 to March 2007 respect to averaged (a) temperature, (b) pressure, (c) wind speed, and (d) relative humidity.
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Fig. 8. Regression plots of SO2 concentration during April 2006 to March 2007 respect to averaged (a) temperature, (b) pressure, (c) wind speed, and (d) relative humidity.
factor causing variation of ambient SO2 concentration. Pressure is the next meteorological factor has the largest contribution on the SO2 concentration variation.
4. Conclusions In this study, the hourly, diurnal, and monthly variations of SO2 concentration during April 2006 to March 2007 were investigated to clarify the affective factors. It was observed that SO2 concentration reach to its maximum value at the mornings during the rush hours, while it reaches to its minimum value at the afternoons when the height of atmospheric mixing layer increases by increasing the temperature. The peak observed during the nights is due to the formation of nocturnal stable boundary and transit of heavy gasoline vehicles around the studied stations. However, a bimodel including traffic and heating related combustion sources is recognized as the main reason which derived the hourly pattern. The weekend effect was also observed in great Isfahan, when SO2 concentration decreases due to decrease the traffic density at the weekends. Furthermore, the industrial around the Isfahn, especially western steel company and power plant, were recognized as the main artificial sources which driving the monthly pattern of SO2 concentration respect to the long term pattern of Isfahan winds. Correlation analysis in addition to a step-wise multiple regression analysis were also implemented to study the effects of meteorological factors quantitatively. It was observed that SO2 concentration is negatively correlated by temperature, sunshine hours, solar radiation, and wind speed, while the opposite was achieved for relative humidity and pressure. Moreover, the
Table 2 Results of regression analysis and equations between SO2 concentration and meteorological factors. Meteorological factor
Equation
R2 (%)
Temperature Wind speed Relative humidity Pressure
102 7.57T 114 2.82WS 9.05 þ 1.24RH 3771 þ 4.53P
23.472 7.904 8.103 13.764
meteorological factors have considerable contribution on the SO2 concentration variations, R2 ¼ 52%. Finally, it was observed that ambient concentration of SO2 in the great Isfahan is in thinkable condition and industries around the city have a considerable effect on that. Hence, it would suggest that all of the Isfahan industries force to utilize SO2 reduction systems. Moreover, seasonal inspections on the cars catalytic converters would be another way to decrease the SO2 concentration level. References Akabueze, C.I., Tsafe, A.I., Itodo, A.U., Uba, A., 2012. Influence of climate and height on the levels of sulfur dioxide (SO2) in Sokoto high traffic density and near atmospheric region. World Environ. 2, 51e55. Atkinson-Palombo, Miller, J.A., Balling Jr., R.C., 2006. Quantifying the ozone “weekend effect” at various locations in Phoenix, Arizona. Atmos. Environ. 40, 7644e7658. Banerjee, T., Singh, S.B., Srivastava, R.K., 2011. Development and performance of statistical models correlating air pollutants and meteorological variables at Pantnagar, India. Atmos. Res. 99, 505e517. Celik, M.B., Kadi, I., 2007. The relation between meteorological factors and pollutants concentrations in Karabük City. G. U. J. Sci. 20, 87e95. Chu, P.C., Chen, Y., Lu, S., 2008. Atmospheric effects on winter SO2 pollution in Lanzhou, China. Atmos. Res. 89, 365e373. EPA, 2011. Six Common Air Pollutants, Sulphur Dioxide. USA. Available via. http:// www.epa.gov/oaqps001/sulphur dioxide/health.html. Flemming, J., Stern, R., Yamartino, R.J., 2005. A new air quality regime classification scheme for O3, NO2, SO2 and PM10 observation sites. Atmos. Environ. 39, 6121e6129. Henschel, S., Atkinson, Zeka, A., Le Tertre, A., Analitis, A., Katsouyanni, K., Chanel, O., Pascal, M., Forsberg, B., Medina, S., Goodman, P.G., 2012. Air pollution interventions and their impact on public health. Int. J. Public Health 57, 757e768. Henschel, S., Queral, X., Atkinson, R., Pandolfi, M., Zeka, A., Le Tertre, A., Analitis, A., Katsouyanni, K., Chanel, O., Pascal, M., Bouland, C., Haluza, D., Medina, S., Goodman, P.G., 2014. Ambient air SO2 patterns in 6 European cities. Atmos. Environ. 79, 236e247. Iqbal, M.A., Kim, K.H., Shon, Z.H., Sohn, J.R., Jeon, E.C., Kim, Y.S., Oh, J.M., 2014. Comparison of ozone pollution levels at various sites in Seoul, a megacity in Northeast Asia. Atmos. Res. 138, 330e345. Jeong, J.I., Park, R.J., 2013. Effects of the meteorological variability on regional air quality in East Asia. Atmos. Environ. 69, 46e55. Khedairia, S., Khadir, M.T., 2012. Impact of clustered meteorological parameters on air pollutants concentrations in the region of Annaba, Algeria. Atmos. Res. 113, 89e101. Luvsan, M.E., Shie, R.H., Purevdori, T., Badarch, L., Baldorj, B., Chan, C.C., 2012. The influence of emission sources and meteorological conditions on SO2 pollution in Mongolia. Atmos. Environ. 61, 542e549. Makara, L., Mayer, H., Mika, J., Santa, T., Holst, J., 2010. Variations of traffic related air pollution on different time scales in Szeged, Hungary, and Freiburg, Germany. Phys. Chem. Earth Part A/B/C 35, 85e94.
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