Analytical Study of Fuel Switching from Heavy Fuel Oil to Natural Gas in clay brick factories at Arab Abu Saed, Greater Cairo

Arab Abu Saed area in Giza governorate, south to Cairo contains more than 228 clay brick kilns represent the largest cluster of brickworks in Egypt. Burning of Heavy Fuel Oil (HFO) in such kilns is the main source of air pollution in the surrounding locations. In this study, investigation of switching the fuel used in brick kilns from (HFO) to Natural Gas (NG) is carried out and the pollution loads are assessed in both cases. In addition, two Gaussian dispersion plume models are employed to estimate the concentration of primary pollutants; PM10, SO2, and NO2 at seven locations in the vicinity of Arab Abu Saed to determine the most adversely affected locations. Statistical analysis is applied to evaluate the correlation and conformity of the results of both models. Results show that using of NG leads to a significant reduction of pollution loads of PM10, SO2 and NO2 reaches 96%, 72%, and 24% respectively. In addition, the reduction of naturally occurring radionuclides in air is analyzed. Activity concentrations of Ra-226, Th-232 and K-40 in Bq/l for HFO were measured using HPGe detector for six HFO samples. Exposure due to air submersion of naturally occurring radionuclides in the study area leads to annual equivalent dose ranged between 2.16 mSv/y (received by Uterus) and 14 mSv/y (received by skin), and average effective dose 2.65 mSv/y which represent valuable exposure.

Results of the dispersion models. The estimation of the highest concentration at 1-hr average of the target air pollutants was done for both scenarios of burning the HFO and NG in the brick kilns. The details of the two Gaussian dispersion models' results are presented in Table (2), it shows that Minya town has the highest concentration of PM 10 , SO 2 , and NO x in case of burning HFO, while the lowest concentration is estimated to be at Tabbin South monitoring station if NG is used. However, Minya town is the most positively affected site of the pollution reduction resulting from the fuel switching.
The predicted 1-hr average concentrations in μg/m 3 of PM 10 , SO 2 , and NO x in case of burning HFO and NG show similarity of the distribution and the locations of the high and low concentrations of the primary pollutants in both scenarios was expected due to the flat terrain of Arab Abu Saed area and the anticipated low wind speed. Comparing the estimated emissions with other studies in the same domain but using different types of fuels (Skinder et al. (2014), Kanabkaew et al. (2015), and Hoang Anh Le et al. (2010)) [17][18][19] , revealed that using biomass fuel is the cleanest way of clay brick production. NG is considered the best alternative in case of burning fossil fuel, while HFO and coal are the worst. statistical analysis. Based on the results given by CGPM and AERMOD, a comparison and statistical analysis were carried out to assess the correlation and conformity between both models. Figure 1 presents the comparison between GCPM and AERMOD results of the highest 1-hr average concentrations of the target pollutants. Table (3) confirmed the correlation and the agreement of both models' results. Consequently, it is concluded that, in case of uncomplicated (flat) surrounding terrain and low wind speed condition, using Power law scheme Radioactivity concentration and equivalent dose. The activity concentrations (Bq/l) of Ra-226, Th-232 and K-40 for six samples of HFO are presented in Table ( 4). It shows that activity concentrations ranged between 1.0 to 1.9, 1.0 to 1.7 and 1.0 to 2.5 Bq/l for Ra-226, Th-232 and K-40 respectively. Although activity concentration is considered low for all radionuclides per one liter, but the daily HFO consumption of each kiln (average 5000 liter per day) leads to dispersion of a considerable activity concentration of Ra-226, Th-232 and K-40 that reach 7000, 6500, and 8000 Bq/day respectively. The calculated annual occupational exposure of Arab Abu Saeed workers is presented in Table ( 5), in which the annual external dose due to average concentrations of all natural radionuclides ranged between 2.16 (received by Uterus) and 14 mSv/y (received by skin). The average effective dose due to exposure to all radionuclides is 2.65 mSv/y.

Materials and Methods
To assess the anticipated improvement resulting from the fuel-switching, CGPM and AERMOD are used and two scenarios are set-up. The first scenario is considering the usage of the HFO in the 176 brick kilns, and measures the pollutants' concentrations at the target locations. The second one calculates the pollutants' concentrations at the same locations in case of burning NG in the brick kilns. The operation of AERMOD and CGPM require obtaining specific data concerning pollutants' emission rates, flue gas velocity, the downwind and lateral distances between the source and receptors, terrain and atmospheric data. The methodology for getting the required data relies on conducting field surveys, carrying out detailed monitoring and measurements, and the relevant previous work in the area which includes; CIDA-pilot project 9 . emission factors and emission rates. Owing to the identical similarity of the production process of Arab Abu Saed brickworks and the difficulties of conducting real measurements for that high number of stacks, it was found that developing emission factors based on the size of production and the type of fuel would be very efficient to elicit emission rates from the stacks of all kilns. Accordingly, to calculate the emission factors, several parameters have to be determined including concentrations of pollutants, the emissions flow rates, the specific consumption of fuel, and the production capacity. Through the conducted field surveys, the amount of fuel used and the production capacity per each kiln were collected. In addition, detailed monitoring and measurements were done for a sample of two kilns per each type of fuel to determine the concentrations of air pollutants and the flow rates (summary of these measurements are presented in Table (6).
The mass emissions per unit time (g/s), unit production (g/ton of Red Brick (RB)) and unit energy used (lb/ MBTU) are the basis of calculating the emission factors in terms of (g/ton RB), however this unit has been converted into another easier unit i.e. (g/1000 RB). The objective is to consider the variation of brick size by using the average density of the produced red bricks in both sets of measurements. The average density of bricks produced by burning HFO is 2.3 kg/RB, while the average density is 2.4 kg/RB if NG is burnt. The resulting Emission factors in case of using HFO are 11380, 3115, and 979 g/1000 RB for PM 10 Table 3. Standard statistical performance of CGPM and AERMOD.
www.nature.com/scientificreports www.nature.com/scientificreports/ Emission factors are 456, 864, 744 g/1000 RB for PM 10 , SO 2 , and NO 2 respectively. Thus, according to the fuel used, the emission load and the subsequent emission rate for each pollutant per each kiln stack are calculated using the following general formula: (1) and the pollution load of e.g. PM 10 for the cluster is estimated as follows:   The velocity of flue gases (m/s) is essential input for both models. The calculation depends on the measured volume flow rate (m 3 /s), fuel consumption rate, and the cross section area of the stack (m 2 ). The general formula for calculating the flue gas velocity (v m/s) is;  where, U 75 is the wind speed at 75 m height. U 10 is the wind speed at 10 m height. h s is the physical stack height (75 m). p is a stability class parameter. H is the effective height above the ground (m) and is generally presented in the form; s 75 where, h s is the physical stack height, Δh is the plume rise (m), w is the exits velocity, D is the internal stack diameter. σ y and σ z can be calculated using different schemes. However, according to 22 , the power law scheme was found to give accurate results in case of U 75 is greater than 2 m/s.
where, a, b, c, and d are Brookhaven National Laboratory Parameters which are determined based on the stability classes. Table 7 presents the assumptions used in the Classical Gaussian plume model calculations of the pollutants' concentrations at the target locations.

AeRMoD. AERMOD is an advanced new generation model developed by US-EPA mainly for regulatory
proposes, and it is commonly used to study the impact of new or existing industrial facilities as well. It can be applied with different types of emission sources (i.e. point, area, or volume sources) and different plume types 24,25 .
It is recommended to be used in Arab Abu Saed case due to its ability to parameterize turbulence and handling www.nature.com/scientificreports www.nature.com/scientificreports/ simple or complex terrain. The Breeze AERMOD software version (7.0.58) is employed to simulate the PM 10 , SO 2 , and NO 2 concentrations at the target locations. It uses Geographical Information System (GIS) based approach to define the model objects, add the terrain relief, and present the results. Consequently, in order to set up the model and run the AERMOD, there are several options required to be filled as discussed below.
Meteorology. AERMOD requires comprehensive meteorological information covering two types of data, one is a surface profile (typically available from the ground weather stations) and the other is the upper surface data (for parameters such as Monin-Obukhov length, albedo, bowen ratio etc. based on radiosonde observations). The Wind rose of the Cairo region based on the annual meteorological data (Fig. 2) was developed in the AERMOD required format. The height of the anemometer instrument is assumed 10 m. The wind rose shows the wind speeds range between 3 to 8 m/s in most periods of the year. Approximately half a year the wind speed reaches 5.14 m/s. The highest frequency wind direction was the northeast.
projection. For setting up the geographical location (latitude and longitude) of the sources and receptors in this model, the Universal Transverse Mercator (UTM) in the World Geodetic system (WGS1984) was used with zone 36 in the northern hemisphere (for Cairo, Egypt). Most of the terrain in and around the cluster is flat, although the terrain on the north and east is moderately complex (hilly) and of heights up to 145 m on the east. Since most of the terrain in the immediate vicinity are less than 10 times the average stack height, terrain do not have a considerable effect on the ambient path of the pollutants released from the stacks of the brick kilns [23][24][25][26] .
The sources of pollutant emissions (176 kiln stacks) were defined on the airshed map using their latitude and longitude. The worst case scenario was designed where pollutants were considered to be released in a constant rate throughout the year without any emission variations.
Receptor options. Seven target receptors were selected and defined on the airshed map. The receptors were placed in the surrounding vulnerable communities and represented different categories such as urban town areas, farmlands, desert areas, and mixed land use areas, as well. The locations of these receptors are; Ikhsas town, Barnasht town, Tabbin town, Minya town, Qibliya town, Tabbin South AAQ station, and Tabbin AAQ station. output options. Two scenarios were set-up to assess the impact of the fuel switching in Arab Abu Saed brickworks clusters; the first one considered the burning of the HFO, while the second scenario showed the result of the fuel switching to NG. In both scenarios, the 1-hr average concentrations of PM 10 , SO 2 , and NO 2 were predicted in the target receptors. Based on the results of afore-elucidated calculation treatments and the survey outputs, Table (8) represents a sample of the input data used in both models, CGPM and AERMOD, for five brick kilns. These data are calculated for the entire cluster (i.e. 176 brick kilns) in order to obtain the substantial environmental impact of the fuel switching.  www.nature.com/scientificreports www.nature.com/scientificreports/ statistical analysis. Different statistical parameters were used to analyze the correlation and agreement between both models. These parameters are Normalized Mean Square Error (NMSE), Fractional Bias (FB), Correlation Coefficient (COR), and Factor of two (FAC2) 27,28 . Radiation measurement. The aim of the radiation measurement is to assess the radiological impact of burning the HFO in the brick kilns and determine the annual effective equivalent dose to the workers due to the exposure to the resulting radionuclides.
the activity concentrations. Six HFO samples were collected randomly from different Brick kilns to measure and calculate the activity concentrations (Bq/l) of Ra-226, Th-232 and K-40. Each sample was packed in plastic cylindrical container; closed tightly and kept for about one month to attain secular equilibrium between Ra −226 and its progenies before exposing to gamma spectroscopy. The γ-spectroscopy used was P-type coaxial (HPGe) with 30% relative efficiency and 2.1 keV FWHM at 1.33 MeV (associated with electronic components), and connected to multi-channel analyzer (MCA). GENE 2000 software program was used to analyze the peak areas of gamma spectra 29 . Activity concentration (A) in Bq/l of each radionuclide in the sample was calculated by using the count rates detected by the HPGe for 24 hours and subtracting the background counts under the selected photo peaks using the following equation; where, N c is the net count rate and equals to (Gross counts per second from the samples -background counts per second), ε is the efficiency of the detector for the specific energy, I γ is the intensity of the gamma ray, m is sample mass in gm, ρ is the density of the HFO sample in gm/l. www.nature.com/scientificreports www.nature.com/scientificreports/ External equivalent and effective organ doses. By using the activity concentration of different radionuclides, the external dose to an organ/tissue H t (mSv/y) can be determined using the specific external dose coefficients for each organ/tissue; h t (Sv.m 3 /sec.Bq), that were calculated by Eckerman and Ryman 30  where, T is the exposure time (5 day/week *50 week/year for workers), For the remainder tissues, the committed equivalent dose H rem can be calculated using the external dose coefficient of remainder tissues h rem which is given 0.2 Sv.m 3 /sec.Bq. The effective dose (E) is the sum of the weighted equivalent doses in all tissues and organs of the body, and can be calculated as: where, W T is the weighting factor of tissue T used to represent the relative contribution of the equivalent dose in a tissue or organ to the total radiation hazard resulting to the body. W T is found in ICRP-60 31 .

Conclusion
The main source of air pollution in Arab Abu Saed Brickworks cluster is burning the fuel in the brick kilns. Switching the used fuel from HFO to NG has resulted in a significant load reduction of air pollutants. By calculating the emission rates of PM 10 , SO 2 , and NO 2 , it is found that fuel switching has led to substantial reductions in sulphur dioxide and particulate (respirable) concentrations in the ambient, while Nitrogen dioxide concentrations have reduced but to a slightly lesser extent. The load reduction of PM 10 , SO 2 , and NO 2 has reached to 96%, 72%, and 24% respectively and this will considerably reduce exposure levels in the near vicinity and bring in health benefits to the nearby population. We can conclude that the reduction in exposure level and the health benefits will occur due to fuels change overall other industries sources and mobile sources rather than brick kilns only Two Gaussian plume models, CGPM and AERMOD, were used to assess the concentration of PM 10 , SO 2 , and NO 2 at seven target locations in case of using HFO and NG scenarios. The results of both models are correlated, in a good conformity, and are factor of 2. Therefore, it is concluded that, in case of uncomplicated (flat) surrounding terrain and low wind speed condition, using Power law scheme to calculate the plume dispersion parameters in CGPM can give accurate results compared to the advanced Gaussian Plume models like AERMOD. The assessment of pollutants' concentrations indicated that Minya and Qibliya towns are the most vulnerable locations affected by the pollution resulting from Arab Abu Saed Brickworks. The radiation measurement of burning HFO in brick kilns showed that, the average concentrations of Ra-226, Th-232 and K-40 per each kiln reached 7000, 6500, and 8000 Bq/day respectively. However, the average concentrations of naturally occurring radionuclides were considerable high; the average dose due to external exposure to different organs or tissues was 2.65 mSv/y. This value within the international permissible values for workers rather than public and it represents valuable exposure that must be taken into considerations.