Assessment of Air Pollution around Durra Refinery (Baghdad) from Emission NO2 Gas at April Month

Nitrogen dioxide NO2 is one of the most dangerous contaminant in the air, its toxic gas that cause disturbing respiratory effects, most of it emitted from industrial sources especially from the stack of power plants and oil refineries. In this study Gaussian equations modelled by Matlab program to state the effect of pollutant NO2 gas on area around Durra refinery, this program also evaluate some elements such as wind and stability and its effect on stacks height. Data used in this study is the amount of fuel oil and fuel gas burn inside refinery at a year 2017. Hourly April month data chosen as a case study because it’s unsteady month. After evaluate emission rate of the all fuel and calculate exit velocity from stack (consider all refinery unit is a point), effective height resulted. Effective height is test with other atmospheric element and with stability, and there is direct relation with unstable turner classes. After Gaussian model implemented results show that most pollutant area from pollutant of NO2 is Al-Jadriyah and Al-Karada area, this area is about 3-5 kilometer from the refinery point. The wind direction domain is from the south to south-east, thus most flow is to north, north-west and the pollutant level of NO2 is over the national ambient air quality standard in this area. Keyword: NO2 concentration, stability, air pollution, April month, emission rate. Introduction: Power generation plants and refinery produce varying emissions to the surrounding atmosphere that may adversely impact air quality and cause air pollution in the vicinity regions 1-2 . Through Combustion of fossil fuels atmospheric nitrogen and any nitrogen in the fuel will converts into its oxides, mainly nitric oxide (NO) and with small amounts (5–10%) of NO2. NO slowly oxidizes to NO2 in the atmosphere 3 . Nitrogen oxides, NOx are the term used to describe the sum of NO, NO2 and other oxides of nitrogen; all these play a major role in the formation of ozone, particulate matter, and acid rain. Long-term exposures to NO2 may lead to increase susceptibility to respiratory infection and may cause permanent alterations in the lung 4 . Usually NO2 in the atmosphere comes from two sources, either directly from emission sources (primary pollutant) or from chemical reactions in the atmosphere 5 . Nitrogen monoxide (NO), in turn, is converted to NO2 by reactions with proxy radicals (RO2) or O3. Nitrogen dioxide is then photolysis in the atmosphere, and the released atomic oxygen combines with molecule O2 to form O3, This gas considers one of gases emitted from flues 6 . Flow rate of Emissions are necessary to determine transfer Contaminants, Where Know the source location will allow us to calculate concentration at a particular region using dispersion model 7 . Inhalation of NO2 by children increases their risk of respiratory infection and may lead to poorer lung function in later life. Recent epidemiological studies have shown an association between ambient NO2 exposure and increases in daily mortality and hospital admissions for respiratory disease. NO2 has also been shown to potentiate the effects of exposure to other known irritants, such as ozone and respirable particles 6 . Animal and human experimental studies indicate that NO2 at short-term concentrations exceeding 200μg/m 3 (one hour) is a toxic gas with significant health effects. Animal toxicological studies also suggest that long-term exposure to NO2 at concentrations above current ambient concentrations has adverse effects 8 . In this study Assessments the effect of the effective rise of Open Access Baghdad Science Journal P-ISSN: 2078-8665 Published Online First: November 2021 E-ISSN: 2411-7986 516 flue on the pollutant resulted from nitrogen oxides emitted from fuel oil and fuel gas combustion in the regions near to refinery for April month that consider as moderate condition month. The study was focus on the factors affecting the pollutant NO2 concentration gas overall. For this purpose the program has built up for simulated arithmetic algorithms, also for precision and ease in the use of equations considered. Site Durra Refinery is the main refinery of Ministry of oil Midland Refineries Company (MRC) in Iraq. It is located on the western side of the Tigris River and south-west of Baghdad city, about few kilometers from the city center, it is flat ground. Refinery has Dimensions length 1620 m and width of 860m. From east bounded with small liquid gas filling plant, and the Imam Hassan neighborhood, also from the west and south-west the university district, the residence of employer’s borders of the refinery. The highway is located on the east, south-east and south sides. Finally, on the northern side, a small flat area extends across the Tigris River; consider one of the largest cities in Baghdad province known as Karada 9 Fig. 1. When refinery builds in 1960 it’s located outside the Baghdad city but the large urban expansion will made the refinery inside the Baghdad city. Figure 1. Location of durra refinery in Baghdad and Iraq Data Durra refinery data The Dura refinery operates 24 hours a day and very large quantities of crude oil are refined to produce oil products, its includes 30 plants represented in twelve units 10 . Table 1 and 2, show stack height and stack diameter also Stack gas exit temp. And other characteristic of these units, these units are considered as sources of 12 points, but because the distance between them is close to each other, it consider as a point source in this study 11 . Period study consist of April month from 2017, see table 2, to know the fuel oil and fuel gas used, where about 27725.3m 3 of fuel oil through 720hour represent total hour of this month through 24hour, this configure in mass about 36890.1kg/hour of fuel oil. But in volumes gas fuel is greater about 6989075m 3 , in mass and equal to about 11163.1kg/hour. At this period (April) most of neutral stability condition is notice over Baghdad city, see reference 12 . From data of fuel oil and gas, emission rate of NO2 can be evaluated according to amounts of fuel burned. Open Access Baghdad Science Journal P-ISSN: 2078-8665 Published Online First: November 2021 E-ISSN: 2411-7986 517 Table 1. The production units in Daura refinery which are used in present study; Symbols, stack information 10 . Item Name of operation unit Symbols Stack’s number stack height Stack diameter(m) Stack gas exit temp.(k) 1 Crude Distillation CDU_1 1 21.7 2.4 640 unit_70000 barrel_1 2 Crude Distillation CDU_2 1 21.6 2.7 612


Introduction:
Power generation plants and refinery produce varying emissions to the surrounding atmosphere that may adversely impact air quality and cause air pollution in the vicinity regions [1][2] . Through Combustion of fossil fuels atmospheric nitrogen and any nitrogen in the fuel will converts into its oxides, mainly nitric oxide (NO) and with small amounts (5-10%) of NO 2 . NO slowly oxidizes to NO 2 in the atmosphere 3 . Nitrogen oxides, NO x are the term used to describe the sum of NO, NO 2 and other oxides of nitrogen; all these play a major role in the formation of ozone, particulate matter, and acid rain. Long-term exposures to NO 2 may lead to increase susceptibility to respiratory infection and may cause permanent alterations in the lung 4 . Usually NO 2 in the atmosphere comes from two sources, either directly from emission sources (primary pollutant) or from chemical reactions in the atmosphere 5 . Nitrogen monoxide (NO), in turn, is converted to NO 2 by reactions with proxy radicals (RO 2 ) or O 3 . Nitrogen dioxide is then photolysis in the atmosphere, and the released atomic oxygen combines with molecule O 2 to form O 3 , This gas considers one of gases emitted from flues 6 . Flow rate of Emissions are necessary to determine transfer Contaminants, Where Know the source location will allow us to calculate concentration at a particular region using dispersion model 7 . Inhalation of NO 2 by children increases their risk of respiratory infection and may lead to poorer lung function in later life. Recent epidemiological studies have shown an association between ambient NO 2 exposure and increases in daily mortality and hospital admissions for respiratory disease. NO 2 has also been shown to potentiate the effects of exposure to other known irritants, such as ozone and respirable particles 6 . Animal and human experimental studies indicate that NO 2 at short-term concentrations exceeding 200µg/m 3 (one hour) is a toxic gas with significant health effects. Animal toxicological studies also suggest that long-term exposure to NO 2 at concentrations above current ambient concentrations has adverse effects 8 . In this study Assessments the effect of the effective rise of flue on the pollutant resulted from nitrogen oxides emitted from fuel oil and fuel gas combustion in the regions near to refinery for April month that consider as moderate condition month. The study was focus on the factors affecting the pollutant NO 2 concentration gas overall. For this purpose the program has built up for simulated arithmetic algorithms, also for precision and ease in the use of equations considered.

Site
Durra Refinery is the main refinery of Ministry of oil Midland Refineries Company (MRC) in Iraq. It is located on the western side of the Tigris River and south-west of Baghdad city, about few kilometers from the city center, it is flat ground. Refinery has Dimensions length 1620 m and width of 860m. From east bounded with small liquid gas filling plant, and the Imam Hassan neighborhood, also from the west and south-west the university district, the residence of employer's borders of the refinery. The highway is located on the east, south-east and south sides. Finally, on the northern side, a small flat area extends across the Tigris River; consider one of the largest cities in Baghdad province known as Karada 9 Fig. 1. When refinery builds in 1960 it's located outside the Baghdad city but the large urban expansion will made the refinery inside the Baghdad city.

Data Durra refinery data
The Dura refinery operates 24 hours a day and very large quantities of crude oil are refined to produce oil products, its includes 30 plants represented in twelve units 10 . Table 1 and 2, show stack height and stack diameter also Stack gas exit temp. And other characteristic of these units, these units are considered as sources of 12 points, but because the distance between them is close to each other, it consider as a point source in this study 11 . Period study consist of April month from 2017, see table 2, to know the fuel oil and fuel gas used, where about 27725.3m 3 of fuel oil through 720hour represent total hour of this month through 24hour, this configure in mass about 36890.1kg/hour of fuel oil. But in volumes gas fuel is greater about 6989075m 3 , in mass and equal to about 11163.1kg/hour. At this period (April) most of neutral stability condition is notice over Baghdad city, see reference 12 . From data of fuel oil and gas, emission rate of NO 2 can be evaluated according to amounts of fuel burned.

Meteorological data
To estimate the dispersion of NO 2 gas concentration, most meteorological factor must be known, to understand the behavior of the pollutant plume. Thus hourly data of air temperature, wind speed, relative humidity, atmospheric pressure, and direction from soda site 13 , is plotted in Fig The effect is started from synoptic scale to release the local effect, for example atmospheric pressure through this month (April) change between 1002.12mb to 1017.91mb. Decreases in the pressure followed by change in wind speed, where its increases resulted from activity in all atmospheric elements at the same period. This atmospheric situation reflected on relative humidity, temperature and also on changes in wind direction. Effect of change in pressure on air temperature, although its small effect, the domain change in air temperature resulted from daily cycle at daytime temperature increases, at nighttime decreases. Monitoring ambient air temperature is very useful to given idea about the height of effective plume rise, while relative humidity effect on the photochemical of some trace gases cause's feedback interaction in pollutant concentration to reach NO 2 gas. Change of wind speed and direction effected on the dispersion of plume pollutant gas and on concentration values level at different region around durra refinery. Max and min values of their element is plotted on graphs, see Fig Stability Atmospheric stability effect on the vertical movement of any aerial parcel, it can be determined by several methods or parameters depend on the data available. In this study empirical turner method is adopted 14 . This method depends on the wind speed record, solar height angle, and total cloud cover over refinery region,(recorded as hourly) see Table 3. Turner method have seven classes, resulted from intersect the table wind speed data, with insolation class number (ICN), at daytime have values from (1)(2)(3)(4), and cloud cover amount at nighttime have negative insolation values (-1 and -2). The amounts of cloud cover available at daytime sometimes modified the ICN, if cloud cover greater than 1/2, and cloud level height less than or equal to 7000ft, where it will became (ICN-2), and if greater than or equal to 7000ft became (ICN-1). If total cloud cover equal to 1 became (ICN-1), where cloud cover level height greater than 7000ft 14 . All this bounded conditions assumed in this method to produce hourly class stability data, that used recently to know concentration of NO 2 dispersion according to Gaussian model in area rounded Durra refinery at April month 2017.

Effective Stack Height:
If neglect effect of turbulent from land surface, and assumed plume is dispered in open area, the effective stack height resulted from a summed stack and plume height ∆H will effected by number of element, concerning stack shape, and external concerning the meteorological factor influence the rise of the plume. The emission interning factors are velocity of the effluent at the top of the stack, v s , temperature of the effluent at the top of the stack, T s and diameter of the stack opening d. The meteorological factors influence plume rise are ambient wind speed, u temperature of the air, T a , shear of the wind speed with height du/dz and atmospheric stability 15 . To calculate plume rise, the buoyancy flux must first be calculated using equation 1 where 16 :

2-stable buoyancy and momentum rise:
To calculate the final plume rise for stable condition, stability parameter s must be evaluated 15 :

Emission rate:
Fuel data from Durra refinery is monthly averages, thus amount of fuel oil and fuel gas divided by 720 hour to get fuel quantity in kg per hours that used to estimated hourly emission rate ( kg/hour) for NO 2 gas, see table 2. Gzar study is adopted as tool to estimated emission rate of NO 2 19-20 , its depend on the emission factor for fuel oil and fuel gas to transformed units for NO 2 gas as follow:  Table 2, emission rate for NO 2 evaluated according to Table 5, below, its notes that emission rate of fuel gas have %09.15 from fuel oil, thus the large rate of pollution in NO 2 come from burned of fuel oil.

Dispersion coefficients
Dispersion coefficients such as σ y and σ z computed from the atmospheric stability class and the downwind distance. The stability class can be computed using the Pasquill or Turner methods 21 . Briggs 1973 examine versions of σ y and σ z , in urban and rural, and provide an interpolation scheme that agrees with Pasquill-Gifford in the downwind range from 100 m to 10 km, except that σ z values for A and B stability approximate the B 2 and B l Brookhaven curves 22 . Table 6 a and b gives the Briggs sigmas. The U.S. EPA recommends these sigma values as the ones most appropriate for dispersion simulations in urban areas 23 .

5-Gaussian plume model:
The Gaussian plume model, which is at the core of almost all regulatory dispersion models, is obtained from the analytical solution of simplified diffusion equation. For a continuous point source released at the origin in a uniform (homogeneous) turbulent flow the solution to diffusion Equation.
Then the final form of the Gaussian plume equation, for an elevated plume released at z = H p is 24 :

6-1 model implemented
The set of equations from 1 to 8 modelling by program, developed to simulate the effect of many elements on the NO 2 concentration gas emitted from the constant source point (Durra refinery). These element ensemble stability classes, wind speed, roughness surface effect, all tested to its effect on NO 2 ground level concentration as an air quality. Procedure outline in number of step as in Fig. 4.

Distribution of stability classes:
Unfortunately there is don't direct measure of stability in refinery location because security difficult, most data obtain from satellites site on internet, thus empirical turner method used to put atmospheric stability at this study, this scheme depend on information in Table 3 and paragraph 4-1. Hourly data of wind speed at 10m, total cloud, and solar angle height used by turner method at April month. Fig. 4 show frequency distribution stability classes, it's about 36% of classes is in class D and 22% at class C , while about more than 30% in classes E and F, this will effect on plume concentration dispersion of NO 2 gas after its emitted from stack. According to Effective stack height paragraph in methodology part equations from 1 to 6 used to calculate hourly effective stack height at April month according to stability classes, unstable included classes A, B, C, D and stable classes E,F,G. average effective height is reached to about 500meter in unstable classes , but this height decreases to more than 30meter in unstable classes, see Fig. 6.

NO 2 concentrations at different distances:
Gaussian model equation 8 for dispersion of NO 2 gas is calculated at different distance from refinery point area. This equation calculate concentration of NO 2 received by ground at different distance 1000m , 2000m…..10000m, also at different domain directions, but this equation need to calculate vertical and horizontal diffusion coefficients of  y and  z , from Table 6, also effective stack height from methodology paragraph. Emission rate at April month for fuel oil and fuel gas is applied in this model equation according to Table 5 Stability classes on concentration amount at different time hours, see Fig. 9. At 1000m distance around refinery point as a circle have this distance as a radius; most NO 2 concentration is very high at range about from 0-12000µg/m 3 , the large values concentrated at stability class F and G or 6 and 7 according to turner classification. In distance 5000m the concentration is in range (0-12000) µg/m 3 , while at 10000m distance from the refinery concentration reduce to range (0-500) µg/m 3 , see Fig. 9. Overall most concentration of NO 2 is over national ambient air quality standard it's about 100 µg/m 3 , this depend on stability class domain.
The most important factor in determine level of pollutant in any area is domain wind direction at specified period. At April month wind direction different from other months it's from south to south east, see Fig. 3, this will causes increases in pollution levels in area located north to north-west of Durra refinery point, see Fig. 10.

Conclusion:
From the analysis of meteorological data, it can be found that Hourly atmospheric parameter in April month has a large change in its values at range (0-9)m/s , (989.3-1027.1)mb, and ( 268.9-324.5)k for wind speed, atmospheric pressure and air temperature respectively. At hours of April month when the domain wind direction is south -east to south south-east, the pollutant plume path will be changed to north-west area. The most frequent stability class considered from turner method is class 4 or D, about 36% from other, this represents the neutral condition. Wind speed calculated at output plume stack is different from wind speed at about 10m in range 0.3 to 2.5m/s, this is because of the difference in hourly stability classes. The highest effective plume height is concentrated at stability classes A and B, and reaches in this study to more than 500m, because of heat convection. Wind speed has a great inverse effect on the value of effective stack height, while temperature affects indirectly. On the other hand, the analysis of fuel data refers to that emission rate resulting from burned fuel oil and fuel gas which are 88.5 and 8.1 g/s respectively. There is a great concentration level of NO 2 at some hour, because of the domain stability classes E,F,G , despite the large distances from refinery point area about 10000m. This concentration level exceeds the national ambient air quality standard 100 µg/m 3 , this depends on stability class domain. The north-west area from refinery such as Jadriyah and Karada located 3-4 kilometer from Dura refinery are considered the most affected areas by NO 2 gas pollutants through this period because in these distances NO 2 pollutant is out of national ambient air quality standard according to World Health Organization (WHO).