Assessing theEffects of Nitrogen Dioxide in Urban Air on Health of West and Southwest Cities of Iran

1. Background

During last two decades, epidemiologic studies throughout the world have evaluated the effect of air pollutionon human being health and related mortality, which showed increase in mortality due to air pollution (1, 2). Common air pollutants in the list of “National Ambient Air Quality Standards” include carbon monoxide (CO), ozone (O₃), PM_2.5, PM₁₀, SO₂, nitrogen dioxide (NO₂), and lead (Pb) (3). Every human being inhales an average of 10-m³ air per day; therefore, assessment of inhaled air effects on health is a vital issue. Predictive models of concentration are classified into deterministic and statistical models. Deterministic models of air pollution, which reflect base condition of turbulence in atmosphere, are applicable tools for modeling gas pollutants and particles; however, their results are always associated with substantial errors. This could be due to partial and brief description of atmosphere-complicated processes in the models. Many factors contribute to such errors among which uncertainty due to intrinsic variability of atmosphere is the most important one. Moreover, the focus of such models is based on the assumption that pollutants are dispersed in a homogenous condition, although practically the earth could be an effective factor in imbalance turbulence in a vertical pathway. In addition, input of the above mentioned models (mainly Gaussian) are frequently based on a simple programming, which assumes turbulence in classes stability atmosphere, while each class includes a wide range of atmospheric stability condition and depends on the place where it is evaluated (4). By utilizing available meteorological and pollution data, and analyzing their statistical correlation, statistical methods are simpler methods for predicting pollutants concentration and their applicability as well as usefulness has been demonstrated by studying short-term predictions of air pollutants using such methods (5, 6). Determination models of health consequences are mostly epidemiologic-statistical, integrating air quality data in concentration intervals with epidemiologic parameters such as relative risk (RR), update base, and attributable fraction, and presenting the result as death toll or mortality (1). Among seven different nitrogen oxides, NO and NO₂ pose health consequences in human being. NO₂ is considered a greenhouse gas that contributes to global warming. NO₂ is a reddish-orange to brown gas with boiling point at 21.2℃ and low partial pressure, which ensure its gas state. It is a corrosive, strong oxidant and a physiologic stimulant of lower respiratory tract with toxicity much more than that of NO. NO₂ is initially formed as NO by combination of azote and oxygen during combustion at an elevated temperature, especially in internal combustion engines and when exhausted, it is rapidly converted to NO₂(7). The main anthropologic sources of the gas include car’s tailpipe, fossil fuels, power stations, industrial boilers, incinerate, and home heating systems. In urban areas, the main source of NO₂ is intra-urban transport system. The concentration of NO₂ changes from day to night. Air quality guidance level for NO₂ is an annual average of 40 μg/m³. Some of its health impacts include increase in Met-hemoglobin (Met-Hb), enzyme activity inhibition, respiratory tract effects, general pathologic effects, and systemic effects (7). In similar work, Goudarzi et al. studied the association between chronic obstructive pulmonary disease (COPD) and NO₂ levels in the Ahvaz in 2009 (8). in addition, Goudarzi et al. studied the association between COPD and NO₂ levels in the Tehran in 2007 and 2011(9, 10). Zalaghi et al. studied the association between COPD and NO₂ levels in the Ahvaz, Bushehr, and Kermanshah in 2010 (11). Furthermore, health effect of air pollution in terms of NO₂, ozone, and particulate matter in most of megacities, particularly Ahvaz, was reported. Health Impact Assessment software (AirQ 2.2.3, developed by the WHO European Centre for Environment Health, Bilthoven Division) was proved to be a valid and reliable tool to estimate the potential short-term effects of air pollution; AirQ predicts health endpoints attributed to criteria pollutants, and allows the examination of various scenarios in which emission rates of pollutants vary (12).

2. Objectives

The present study aimed at estimating and comparing epidemiologic indices attributed to the pollutant NO₂ in the urban air of southwest cities of Iran, namely, Ahvaz, Kermanshah, and Bushehr in 2011.

3. Materials and Methods

In the present study, data relevant to the air-pollutant NO₂ in 2011 were obtained from the Iranian Department of Environment as a Microsoft Excel file format. Since all air pollution measurement stations were lacking temperature sensors, 24-hour and daily air pressure and temperature data were collected from meteorological organizations of the studied cities. NO₂ concentration was expressed in volume/volume percent (v/v), which was subsequently converted to mass/volume percent (m/v) using following calculations (13, 14):

Formula (1): B1 = 273.15 + A1

Formula (2): D1 = (1013.25 × e [-(0.0342 ×C1)/B1] )

Formula (3): E1 = D1/1013.25

Formula (3): G1 = [(273.15 × E1) × (2.05 × F1)]/B1

Where A is temperature (℃), B is temperature (kelvin),C is pressure (mbar), D is pressure (atm), E is ratio P/P0, G is concentration NO₂ (ppb), and F is concentration NO₂ (µg/m³)(8, 9, 12). Primary processing including eliminating, sheet classifications of pollutant, and temporal homogenizing for mean estimation, secondary processing including code writing, mean calculation, and condition correction, primary filtering, secondary filtering, and Finally, using following equations, RR and attributable fraction of the pollutant NO₂ was obtained in three studied cities. Thereafter, 24-hour means were calculated for NO₂ pollutant. We estimated the health impact that was attributable to the exposure of air pollution on the target population using AirQ model, which estimates the impacts of specific air pollutants on a resident population in a certain area and period. Attributable proportion (AP) may be obtained by the following equation (15):

AP = SUM ([RR(c) - 1] P (c)) z/SUM [RR(c) P (c)]

where RR(c) is RR of health implications in the group c or any group of interest, and P(c) is population proportion of the group c or any group of interest. RR of selected health implications is obtained using response-exposure functions (15)

RR = Probability of event when exposed/Probability of event when non-exposed

3.1. Study Regions

Ahvaz, the capital of Khouzestan Province, Iran, with an area of 8,152 km², lies on the geographical coordinates of 30° 45' to 32° N, 48° to 49° 29' E, southwest of Iran, with height of 22.5 m above sea level (16). Its climate is hot and humid. Kermanshah, the capital of Kermanshah Province, Iran, lies on the geographical coordinates of 34° N, 47° 4' E in the middle of the western part of Iran, whose climate is semiarid and mountainous temperate (17). Kermanshah’s height is 1200 m above sea level. Bushehr is the capital of Bushehr Province, Iran, with coordinates of 28° 95' 76" N, 50° 83' 71" E and with an area of around 1441 km² (18) (Figure 1).

Study Areas Map (Ahvaz, Bushehr,Kermanshah)

Figure 1.

Study Areas Map (Ahvaz, Bushehr,Kermanshah)

4. Results

Table 2 shows that in summer, winter, and the whole year 2011, Kermanshah and Bushehr had on average the maximum and minimum NO₂ concentrations, respectively. In addition, according to the results, concentration of the pollutant NO₂ in 2011 was more in winter than in summer in any of the three studied areas. The indices of RR, attributable percentage, and attributable cases of NO₂ for myocardial infarction (MI) with baseline incidence of 132 were calculated (Table 3). According to calculations, RR in the three studied cities for acute MI was estimated 1.0036. In addition, accumulative number of cases attributed to exposure with NO₂ in the studied cities was maximum (21 cases) in Kermanshah and minimum (one case) in Bushehr. RR attributed to NO₂ for COPD was estimated 1.0038 and the accumulative numbers attributed to COPD were eight and 19 in Kermanshah and Bushehr, respectively. Therefore, Kermanshah had the maximum cases of COPD among the three studied areas. Studied implications due to NO₂ for calculated RR in study areas (Ahvaz, Bushehr, and Kermanshah). Figures 2 - 4 show health implications due to NO₂ based on accumulative number of cases and epidemiologic indices. RR attributed to NO₂ for mortality due to cardiovascular diseases (CVD) was estimated at 1.002 at intermediate level. In addition, accumulative number of death due to CVD attributed to exposure to NO₂ in the studied cities was maximum (44 cases) in Kermanshah. Figures 2 and 3 illustrate that despite the estimated RR, health impacts of NO₂ in concentrations < 20 μg/m³ was zero due to lack of public exposure to such concentration. In other words, there was no day with concentration < 20 μg/m³ in Ahvaz and Kermanshah. Figure 4 indicates that despite the estimated RR, health impacts of NO₂ in concentrations < 10 μg/m³ was zero due to lack of public exposure to such concentration. In other words, there was no day with concentration < 10 μg/m³ in Bushehr.

Accumulative Number of Cases of Myocardial Infarction due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

Figure 2.

Accumulative Number of Cases of Myocardial Infarction due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

Accumulative Number of Cases of Cardiovascular Diseases Due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

Figure 3.

Accumulative Number of Cases of Cardiovascular Diseases Due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

. Accumulative Number of Cases of Chronic Obstructive Pulmonary Disease Due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

Figure 4.

. Accumulative Number of Cases of Chronic Obstructive Pulmonary Disease Due to Nitrogen Dioxidein Concentration Intervals in Ahvaz, Bushehr, and Kermanshah Cities in 2011

5. Discussion

According to the results, the accumulative number of MI attributed to exposure with NO₂ in 2011 was 19 (10 cases more than in 2010). About 56% of MI had occurred in days with concentration < 70 μg/m³. On the other hand, 80% of the cases had occurred in days with concentration of NO₂< 100 μg/m³. Regarding intermediate level of RR, the accumulative number of CVD due to exposure with NO₂ was 40 (21 more than in 2010) in which 66% were related to concentration < 80 μg/m³. Low values of attributable percentage of COPD indicate low RR at low level (5%); hence, the numbers of the cases in accumulative central level was estimated at 15 (18 cases more than in 2010). The indices of RR, attributable percentage, and attributable cases to NO₂ for MI with baseline incidence of 132 were calculated. According to the results, accumulative number of MI attributed to exposure to NO₂ in 2011 was 21. Moreover, 41% of MI cases had occurred in days with concentration < 70 μg/m³. On the other hand, 82% of the cases had occurred in days with concentration of NO₂< 100 μg/m³. Regarding intermediate level of RR,the accumulative number of CVD due to exposure to NO₂ was 44 in 2011, in which 57% were related to concentration < 80 μg/m³. Accumulative number of COPD attributed to NO₂ was estimated at 17. Based on the results, total cumulative number of MI attributed to exposure with NO₂ was two in Bushehr in 2011 and 45% of MI cases had occurred in days with concentration < 80 μg/m³. Accumulative number of CVD cases, regarding intermediate level of RR due to exposure with NO₂ was three in 2011, in which 45% were related to concentration < 30 μg/m³. Moreover, Accumulative number of COPD attributed to NO₂ was only one in 2011.

Among the three study areas (Ahvaz, Bushehr, and Kermanshah cities), maximum and minimum annual averages of NO₂ concentration were reported from Kermanshah (63.58 μg/m³) and Bushehr (27.76 μg/m³), respectively. The observed increased NO₂ concentration in Kermanshah might be due to increase in home heating systems, and more burning fossil fuels, and topographical conditions of the region, which led to more stability of the pollutants in atmosphere in comparison with Ahvaz and Bushehr. The obtained results in Toronto, Canada, showed that the number of referrals to hospitals due to COPD was 7.72 cases of which 40.4% were due to exposure with NO₂(19). Goudarzi utilizes AirQ model for estimating health impacts of NO₂ in Tehran, Iran, in 2007. According to the results, about 18% of total deaths due to CVD, 3.8% of MI, and 4.06% of hospital referrals due to COPD were attributed to concentrations > 40 μg/m³(10). Goudarzi et al. attributed about 0.38% of total deaths due to CVD, 0.69% of MI, and 0.73% of hospital referrals due to COPD to concentrations > 20 μg/m³(8, 9). In addition, about 0.83% of deaths due to CVD, 1.48% of MI, and 1.57% of hospital referrals due to COPD were attributed to concentrations > 20 μg.m^-3. Comparing the results in Ahvaz, Tehran, and Toronto, suggests that the more percentage regarding death of the two implications in Ahvaz may be related to higher average of NO₂ and/or days with higher concentrations in comparison to 2010. In 2011, the maximum number of observed death cases attributed to NO₂ in Kermanshah were due to CVD (1.06%), acute MI (1.8%), and COPD (1.9%) with concentration > 20μg/m³. On the other hand, the minimum number of death cases was seen in Bushehr due to CVD (0.03%), acute MI (0.06%), and COPD (0.6%) with concentration > 20 μg/m³. Every 10 μg/m³ increase in the concentration of the pollutant NO₂ in the cities of Ahvaz, Kermanshah, and Bushehr led to increase in the RR of MI, CVD, and COPD by 0.4%, 0.2%, and 0.4%, respectively, in 2011.