since the industrial revolution , the rate of industrialization and urbanization has increased dramatically . regarding this issue , specific regions mostly located in developing countries have been confronted with serious problems , particularly environmental problems among which air pollution is of high importance ( 1 ) . in order to manage this problem , air quality indices are the most widely used tools which mainly indicate the quality of air in a specific region . in fact , air quality indices are widely used in air quality management schemes . main air quality index being applied over the world is air quality index or aqi ( usepa , 2009 ) developed by united states environmental protection agency ( 2 ) . in this index , one can calculate the quality of air by entering required values of major pollutants ( i. e. co , so2 , pm10 , pm2.5 , o3 , and no2 ) . since the air quality indices have been deeply discussed in previously conducted studies , further details can be found ( 1 , 38 ) . as it mentioned earlier , an air quality index not only shows the quality of air , but also can be used to design specific plans in handling air pollution . however , previously developed air quality indices have been mentioned to have main limitations . in a study ( 1 ) it was mentioned that the applicability of usepa aqi in specific areas which are not similar to united states is limited . this index had been developed based on the quality of air and also the major pollutants in united states . other limitations not related to the present study are discussed in detail in previously conducted studies ( 3 , 9 ) . considering the fact that pollutants are being emitted into the air from various sources , it is wise to think that some of the pollutants are indigenous to specific regions . in addition to this , these pollutants are not included in abovementioned index or other air quality indices developed around the world . ( 1 ) an air quality , namely , fuzzy air quality index was developed . by comparing the result of faqi with usepa aqi , they indicated that the major part of pollution is resulted from specific pollutants which are normally ignored in routine assessment of air quality ; in other words , the pollution was mostly caused by benzene , toluene , xylem , and ethylbenzen . in other developed indices for assessing water quality , it has also been shown that the quality is mostly rooted from parameters not normally assessed . considering the fact that an air quality index is a tool by which we are able to make plans so as to manage the problem when it is necessary , the mentioned problem can gravely affect our decision . therefore , to the best of our knowledge , very few studies have been conducted aiming to indicate the local pollutants of different regions around the world . the present study was aimed to indicate the major pollutants of tehran , iran , which is a highly populated area with a total population of approximately 10 million . eleven parameters , including co , so2 , pm10 , pm2.5 , o3 , no2 , benzene , toluene , ethyl - benzene , xylene , and 1,3-butadiene , have been accounted over a period of two years ( 20112012 ) from five monitoring stations located at tehran . in fact , we selected these parameters to assess their concentrations and presence over a period of two years so as to find the major air pollutants of tehran . at first , a set of input - output fuzzy parameters was defined for each mentioned parameter to have it is fuzzy based monthly quality ; and also , fuzzy c - mean clustering was used to find the major part of each pollutant in the total quality of air in tehran , iran . furthermore , the number of times , in monthly basis , which each pollutant s level had been higher than its set standard level are extracted in order to have a deep understanding of the quality of air in this area . fuzzy logic , suggested by zadeh ( 10 ) , as a tool for which is capable of thinking much more like the way human beings do . over the past decade , fuzzy logic has been widely used to model and control complex systems ( 1 , 11 , 12 ) . to develop a model by using this tool , we are able to use an individual s existing knowledge and experience as information ( 13 ) . this property of fuzzy logic can be considered one of its main advantages not considered by other methods . there have been various models developed based on fuzzy logic ( 1 , 11 , 12 , 14 , 15 ) . this process requires knowing three main parts of the fuzzy inference system , including membership functions , fuzzy set operations and inference rules ( 13 ) . here called the universe of discourse had been defined for each input and output ( set ) divided into subsets and expressed by using linguistic terms . 1 were selected based on the terms used to define the air quality in usepa aqi . we used trapezoidal membership functions based on the following equation and table 1 : 
 trapezoidal  :  f(x;a , b , c , d)={0x < a  or  d < x(ax)(ab)axb1bxc(dx)(dc)cxd } 
  fuzzy sets and linguistic terms for the inputs and the output in order to assign each subset to its corresponding subset in the output , fuzzy if - then rules were defined by extracting experts knowledge . for each input - output relationship the following rules are the examples of what we used in this study : 
 rule 7 : if pm2.5 
 is  low  then quality is  moderate  . rule 7 : if pm2.5 
 is  low  then quality is  moderate  . rule 42 : if so2 
 is  extremely high  then quality is  hazardous  . all computations were carried out using the  fuzzy logic toolbox  in matlab version 7.9.0 fuzzy c - means ( fcm ) , originally introduced by bezdek ( 16 ) , is a technique in each data point belongs to a cluster to some degree that is specified by a membership grade . by using this technique , we are able to group data points , in this case concentrations of abovementioned parameters , into a specific number of different clusters . in fact , the purpose of using this method is to have the best structure regarding the applied data ; and also , this method provides us with the ability to partition the data set into groups with similar individuals . the raw concentration of each parameter ( monthly average ) was entered to the program . in other words , most of the parameters concentrations were following a same trend individually . in fact , we assessed the concentration and duration of the pollutants over a period of two years . hence , the group studied in this work was included of eleven parameters ( i. e. co , so2 , pm10 , pm2.5 , o3 , no2 , benzene , toluene , ethyl - benzene , xylene , and 1 , 3-butadiene ) . the concentration of these pollutants , which are routinely monitored by air quality administration , was collected from five monitoring stations , namely , aghdasieh , poonak , park roz , geophysics , and shahre rey . tehran , the capital city of iran , is one of the most populated cities around the globe with a total population of approximately 12 million . based on the reports of previously conducted studies , the major sources of air pollution in this city are motor vehicles and industries . due mainly to prevailing west - to - east winds and also the location of main industries at the west part of this city , wide range of pollutants , especially those with industrial origin(i . fuzzy logic , suggested by zadeh ( 10 ) , as a tool for which is capable of thinking much more like the way human beings do . over the past decade , fuzzy logic has been widely used to model and control complex systems ( 1 , 11 , 12 ) . to develop a model by using this tool , we are able to use an individual s existing knowledge and experience as information ( 13 ) . this property of fuzzy logic can be considered one of its main advantages not considered by other methods . there have been various models developed based on fuzzy logic ( 1 , 11 , 12 , 14 , 15 ) . this process requires knowing three main parts of the fuzzy inference system , including membership functions , fuzzy set operations and inference rules ( 13 ) . here called the universe of discourse had been defined for each input and output ( set ) divided into subsets and expressed by using linguistic terms . 1 were selected based on the terms used to define the air quality in usepa aqi . we used trapezoidal membership functions based on the following equation and table 1 : 
 trapezoidal  :  f(x;a , b , c , d)={0x < a  or  d < x(ax)(ab)axb1bxc(dx)(dc)cxd } 
  fuzzy sets and linguistic terms for the inputs and the output in order to assign each subset to its corresponding subset in the output , fuzzy if - then rules were defined by extracting experts knowledge . for each input - output relationship the following rules are the examples of what we used in this study : 
 rule 7 : if pm2.5 
 is  low  then quality is  moderate  . rule 7 : if pm2.5 
 is  low  then quality is  moderate  . rule 42 : if so2 
 is  extremely high  then quality is  hazardous  . all computations were carried out using the  fuzzy logic toolbox  in matlab version 7.9.0 fuzzy c - means ( fcm ) , originally introduced by bezdek ( 16 ) , is a technique in each data point belongs to a cluster to some degree that is specified by a membership grade . by using this technique , we are able to group data points , in this case concentrations of abovementioned parameters , into a specific number of different clusters . in fact , the purpose of using this method is to have the best structure regarding the applied data ; and also , this method provides us with the ability to partition the data set into groups with similar individuals . the raw concentration of each parameter ( monthly average ) was entered to the program . in other words , most of the parameters concentrations were following a same trend individually . in fact , we assessed the concentration and duration of the pollutants over a period of two years . hence , the group studied in this work was included of eleven parameters ( i. e. co , so2 , pm10 , pm2.5 , o3 , no2 , benzene , toluene , ethyl - benzene , xylene , and 1 , 3-butadiene ) . the concentration of these pollutants , which are routinely monitored by air quality administration , was collected from five monitoring stations , namely , aghdasieh , poonak , park roz , geophysics , and shahre rey . tehran , the capital city of iran , is one of the most populated cities around the globe with a total population of approximately 12 million . based on the reports of previously conducted studies , the major sources of air pollution in this city are motor vehicles and industries . due mainly to prevailing west - to - east winds and also the location of main industries at the west part of this city , wide range of pollutants , especially those with industrial origin(i . as shown in this figure , monthly averages of these pollutants are mostly lower than set standard levels by epa . 2a ) at different sampling stations , except shahr - e - rey , were mostly below the standard level of 9 ppm ( usepa , 1997 ) . it can be seen from this figure that the mean average concentrations of these pollutants exceed the standard levels in most months of study period . 3a ) are dramatically higher than the standard level of 5 ppb at all sampling stations . monthly mean concentrations of criteria air pollutants for the study period at different sampling stations monthly mean concentrations of btex and 1 , 3-butadiene air pollutants for the study period at different sampling stations table 1 indicates the individual quality of each pollutant in all the sampling stations derived by using fuzzy inference system . the fuzzy based quality of criteria pollutants can not be considered as a threat to human health . for instance , the quality of benzene and toluene is mostly e and/or f , indicating a hazardous condition . based on the results , almost all the clusters deduced for the criteria pollutants centered lower than the set standard level . the concentrations of btex and 1,3-butadien are centered in almost all the sampling stations around the clusters representing the hazardous condition of air quality . in fact , these results show that relying on the index developed by usepa can not be a suitable option , since the main threat roots from the pollutants not included in that index . fcm of the monthly mean concentrations of btex and 1 , 3-butadien pollutants in aghdasieh ( sampling stations ) fcm of the monthly mean concentrations of btex and 1 , 3-butadien pollutants in geophysics ( sampling stations ) based on the results of the present study , it can be implied that the application of epa aqi is not suitable in regions with different air pollutants . in fact , the application of this index in regions with various sources of air pollutants and different range of pollutants could results in underestimating the quality of air . in other words , epa aqi is included only with six parameters ; whereas , there are many other pollutants emitted from varios sources ( i. e. industry , and motor vehicles ) which are abundantly present in mega cities like tehran . in a study conducted by sowlat et al . the index developed by them indicates a more stringent result , in comparison with that of epa aqi . they reported that this difference is due to the difference in the number of pollutants included in each air quality index . the present study does not aim to consider the total air quality of tehran , since previously conducted studies have shown that the current aqi index ( epa aqi ) is not suitable for indicating the quality of air in this city . we also tried to further analyze the quality of air between 2011 and 2012 by using fuzzy c - mean clustering . based on the results , the monthly mean average concentrations of criteria pollutants in all the sampling stations are lower than the standard level . this is also in line with the results of the study conducted by sowlat et al . if one uses epa aqi to assess the quality of air between the year 2011 and 2012 , the quality of air resulted from using this index would not be what in the reality is . in other words , the results achieved for btex and 1 , 3 butadiene which are shown in fig . 4 and 5 for respectively aghdasieh and geophysics sampling stations confirm that the quality of air in these years is indeed affected by the parameters not included in the index developed by usepa . considering the fact that an air quality index is developed to not only show the quality of air , but also be used as a tool to develop managerial plans , relying on the output of such index can results in completely different outcomes . the real problem can be missed , since the main pollutants are ignored in this index . annually , a considerable amount of money is spent to improve the quality of air in tehran . however , this all can be wasted if we do not know where the problem is rooted from . the present study was conducted with the aim of assessing the main air pollutants of tehran , iran between 2011 and 2012 . a broad range of air pollutants exist in the environments jeopardizing the health of human beings . it showed that the main pollutants of this city are not what general public believes . in fact , the main threats come from the pollutants which are not currently included in the air quality index developed by usepa . in the present work , eleven parameters were assessed by using fuzzy inference system and fuzzy c - mean clustering . these tools showed that the quality of criteria pollutants between the year 2011 and 2012 did not as much effect the public health as the other pollutants did . iit is clear that by using the air epa aqi , the quality of air , and also the managerial plans required to improve the quality can be misled . ethical issues ( including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc . ) have been completely observed by the authors .
background : since the industrial revolution , the rate of industrialization and urbanization has increased dramatically . regarding this issue , 
 specific regions mostly located in developing countries have been confronted with serious problems , particularly environmental problems among which air pollution is of high importance.methods:eleven parameters , including co , so2 , pm10 , pm2.5 , o3 , no2 , benzene , toluene , ethyl - benzene , xylene , and 1,3-butadiene , have been accounted over a period of two years ( 20112012 ) from five monitoring stations located at tehran , iran , were assessed by using fuzzy inference system and fuzzy c - mean clustering.results:these tools showed that the quality of criteria pollutants between the year 2011 and 2012 did not as much effect the public health as the other pollutants did.conclusion:using the air epa aqi , the quality of air , and also the managerial plans required to improve the quality can be misled .