Spatial and Temporal Variations of PM2.5 Concentration and Air Quality in Isfahan City in 2016

1 Student Research Committee, Department of Biostatistics, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. 2 Department of Environmental Health, School of Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3 Department of Biostatistics, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. 4 Department of Biostatistics, School of Health, Kermanshah University of Medical Sciences, Kermanshah, Iran.


Introduction
Nowadays most of the major cities in the world face with environmental problems, which are at the top of the unfavorable condition of air quality. As a result, the exposure of citizens to polluted air in large cities is unavoidable 1 .
The term PM indicates particulates or droplets transmitted through the air, which can have production sources and variable sizes 2 . Smaller particles (especially PM2.5) have a greater penetrating potential in the lungs and may even reach the alveolus region, therefore, they can have more short-term and long-term effects, such as early death, increased symptoms of respiratory diseases, decreased lung function and changes in the pulmonary tissues 3,4 . The diverse health effects of PM depend on the chemical and physical compositions (mostly its chemical composition) 5 .
Smaller particles comprise a small amount of PM but they are much more important in terms of health 6 because their number is high and have more surface area and can carry toxic pollutants such as heavy metals and organic compounds. These particles are largely produced by combustion engines 7 .
The effects of PM include irritation of the throat and nose, severe lung injury, bronchitis and asthma, allergies, and early death. According to WHO estimations, the mortality rate increases by 1 to 3 percent for every 10 μg/m 3 of PM. Therefore, the need to study the properties of PM and how they propagate along with the determination of the origin of these particles in different cities is one of the priorities of the air pollution control program in urban areas [8][9][10][11] .
Several studies have been done to investigate the air pollution situation in cities. Concluded that long-term exposure to inhaled small particles, increases the risk of lung cancer and death from cardio-pulmonary complications 10 . A study conducted by Chan C in Beijing found that 86% of PM2.5 samples were found to exceed the EPA 12 . Another study in Delhi showed that maximum PM2.5, PM10 particles concentrations occur at peak traffic levels 13 .
Mokhtari et al., in a study evaluated the health effects of exposure to PM2.5 in the air of the city of Isfahan. Their study showed that 8.1% of all nonrandomized deaths recorded in the year 2013 in the city of Isfahan were due to PM2.5 14 .
In another study Jafari et al., distributed the air pollutants and estimated the mortality rate in Isfahan. The results of this study showed that 15.8% of the total mortalities in Isfahan were related to the pollutants which were studied in this study 15 .
Moreover, Farrokhzadeh et al., estimated the spatial distribution of lead, radon and PM10 in Sepahan, Isfahan, using GIS. The results of the study indicated a high concentration of PM10 in this region 16 .
In another study, Jafari et al. evaluated the spatial and seasonal variations of air quality indicators in Isfahan using GIS. The results of this study showed that Ahmedabad station has the highest rate of pollution in Isfahan. The rate of air quality index in Isfahan was only in a healthy condition for 4 days 17 .
Azizfar et al., in a study determined the concentration of PM2.5 and calculated the air quality index in Qom. The results of this study showed that PM2.5 contaminated with the average of 33 µg/m 3 , was the most polluted and August, September and October with average of 8 μg/m 3 were the clean months, as well as the rate of air quality index in most cases was less than standard 18 .
Gholampour, studied the concentration of PM in Tabriz, concluded that the concentration of PM2.5 was 69% of the national standard (10 μg/m 3 ) and the standard level (25 μg/m 3 ) of EPA was 50% higher than the standard. The PM of Tabriz is often beyond the standard limits 19 .
The air pollution crisis has become a serious issue in some cities in Iran including Isfahan 20 . The city of Isfahan, with an area of about 106 km 2 , with a population of 2 millions, hundreds of thousands of cars, consumption of millions of liters of gasoline, polluting industries such as refineries, petrochemicals, industrial towns around, is one of the largest and the most polluted city in Iran 21 . Due to the importance of hygiene in PM in the air, present study addresses the temporal and spatial changes of PM of less than 2.5 (PM2.5) and air quality indicators in Isfahan in 2016. It is hoped that the results of this study could help policymakers design integrated air quality management and plan to prepare themselves to deal with the effects of this phenomenon.

Materials and Methods
The study area City of Isfahan is located at 32 degrees and 38 minutes' north latitude and 51 degrees and 39 minutes' east longitude in central of Iran with an average elevation of 1570 meters above sea level on the Zayanderud coast. Figure 1 shows the studied area and air pollution sensing stations in Isfahan.

Study Type and Time Range
This descriptive-analytic, cross-sectional study was done in Isfahan in 2016. Due to the limited number of air pollution sensing stations, all the information obtained from all these centers is used. These include the stations of Ahmadabad square, University blvd, Rudaki street, Chaharbagh Khajoo, Kharrazi highway and Imam Hossein square. All of these stations are managed by Isfahan EPA. The measurement of PM2.5 concentrations in the form of the hour is measured at pollution stations in the city of Isfahan. Data related to the meteorological variables including humidity and temperature was obtained from the meteorological organization.

Air Quality Index
Air pollution index indicator was used to express air pollution in mass media. In 1999, the US Environmental Protection Agency (U.S.EPA) introduced the Air Quality Index (AQI) to express the severity of air pollution. The AQI has been shown to measure the effects of contaminated air on health. The index of this indicator, carbon monoxide, ozone, suspended particles, sulfur dioxide and nitrous oxide is converted to the air quality index using the formula. After the calculations, a number is obtained between 0-500 which is divided into different ranges and each range shows the amount of air pollution and provides the necessary advice.

Analysis
Descriptive indicators of pollution were determined using mean and standard deviation. Charts were plotted using SPSS and Excel software.
In this study, the frequency of the desired variable (PM2.5 contaminant concentration and air quality index proportional to it) was investigated based on the days of the week, season, and month.

Ethical issues
This article is derived from the master thesis of Biostatistics, with the code of ethics "IR.MUI.REC. 1396.3.577".

Results
According to the hourly measurement of PM2.  (Table 1). Figure 2 shows the daily change in PM2.5 concentrations. The highest daily concentration of PM2.5 is equal to 117.89 µg/m 3 on 2nd October and the lowest daily PM2.5 concentrations is equal to

Variations of PM2.5 Concentration and Air Quality in Isfahan City
Jadidi H, et al. (3), Issue (4), December 2018, 557-66 Jehsd.ssu.ac.ir 4 14.82 on the 20th April. The total number of 242 days (66.3%) is higher than the daily standard. Figure 3 shows seasonal mean PM2.5 concentrations in the seasons of spring, summer, autumn and winter. The average PM2.5 concentrations in these four seasons are 24.53 and 27.59, 34.03 and 33.54, respectively. The results indicate that winter has the highest and that the spring has the lowest concentration of PM2.5 . Figure 4 also provides a weekly overview of the PM2 concentration. This chart shows that the highest concentration of PM2.5 , is on Saturdays and Sundays and the lowest concentration of PM2.5 , is on Fridays and Tuesdays.

JEHSD, Vol
In table 2, the air quality of the city of Isfahan over the entire sampled days in 2016 is categorized according to AQI Index.
The results show that the weather conditions in Isfahan city (80%) were 299 days moderate (18%), 66 days in an unhealthy condition for sensitive groups, and (2%) 4 days in unhealthy conditions for all groups.
Also Table 3 shows monthly meteorological data. The results recorded show that the minimum temperature was in February and the maximum temperature was in July. Also, the minimum humidity level was recorded in December and maximum humidity level was recorded in September. The overall average temperature and humidity in Isfahan in 2016 was 15.60 degrees and 26.98 percent respectively. The dispersion map of PM2.5 concentrations in Isfahan city was drawn in Figure 5 which shows that PM2.5 concentrations in the center of Isfahan is more than other areas.

Discussion
PM2.5 pollutants are one of the main air pollutants in the city of Isfahan and has severe damaging effects on human health.
The results of this study showed that the highest mean of PM2.5 concentrations in Isfahan was observed in cold months of the year; November, December and February, and the lowest mean of concentration in the warm months of the year was in April, May, and August.
Aziz far et al., in a study in Qom in 2011, studied the amount of PM in Qom in different months of the year, based on PM2.5 concentration, December was the most polluted month with average 33 μg/m 3 and August, September and October were the most cleanest months with the average of 17 μg/m 3 22 .
The average concentration of PM in winter and autumn is higher than the average PM in the spring and summer. Because of the presence of air inversion in the cold months of the year and the increased use of fossil fuels for fuel vehicles and heating of homes, concentration of pollutant particles in the city of Isfahan have been increased. It is consistent with the results of the Gholampour study in Tabriz and Mokhtari's study in Yazd 23,24 .
While studies by Islami and colleagues in Kermanshah 25 and Ammar Luie et al 26 in Ilam reported the highest concentrations of PM in the summer, the reason for this is that the incidence of entrapment neighboring countries in the western part of the country. According to the results of this study and monthly calculation of PM2.5 contamination and air quality index, it was found that Isfahan, in 2016, had 296 days of healthy and 70 days of unhealthy conditions. Mean and standard deviation of PM2.5 concentrations in the whole period of 2016-2017 was 29.87±10.9 μg/m 3 . Furthermore, the PM2.5 concentration dispersion map shows that PM2.5 concentrations in the central parts of the city of Isfahan have the highest concentrations. Mokhtari et al 14 also studied the changes in PM2.5 concentrations in Isfahan in 2013, which showed that the highest concentration of PM2.5 concentrations in the center of Isfahan is consistent with the present study.
The reason is the high traffic volume and high population density in these areas. One of the most important factors in increasing of PM2.5 concentration in urban environments is high traffic and vehicle combustion 27 . Chart of daily changes in PM2.5 concentration showed that in most days of the year 2016, almost among the most stations of the city of Isfahan, it was higher than the WHO standard (25μg/m 3 ). The results of the study by Gholampour et al. in Tabriz, which investigated the changes in PM in the city, showed that the amount of PM in Tabriz city is more than the WHO standard for most days of the year 19 . It can be said that increase in population, vehicles, tourism and industries around Isfahan is not reasonable.

Conclusion
The present study showed that in most days and months of the year, the concentration of PM2.5 in Isfahan was higher than the WHO (25 μg/m 3 ), and the mean PM2.5 concentrations in the cold seasons was higher than the mean PM2.5 concentrations in the warm seasons. It seems that the growth, control and management of this pollutant are essential for the health of citizens and reduction of unhealthy effects.

Limitations
Among the limitations of the study, a few number of pollutant stations in the city of Isfahan were noted. The most pollutant stations in the city of Isfahan were focused in the center of the city and in close proximity. Likewise, the lack of measurement of meteorological variables in each station is another limitation of this study.

Suggestions
Finally, it is suggested that the results of this study should be used to monitor air pollution in Isfahan and other important contaminants of Isfahan in the future should be studied simultaneously using spatial-temporal models and its relation to diseases in Isfahan in future research should be investigated.