Modeling the distribution of suspended particles in the south of Tehran by the model of AERMOD, (A Case Study of Tehran cement factory)

Introduction
Air pollution is the introduction of particulates, biological molecules, or other harmful materials into the Earth's atmosphere, possibly causing disease, death to humans, damage to other living organisms such as food crops, or the natural or built environment. The atmosphere is a complex natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has been recognized as a threat to human health as well as to the Earth's ecosystems. The cement industry has 79 years record in Iran and with total cement annual production capacity of 66 million tons; is the largest cement producer country in the Middle East. In the various stages of production process of the material many pollutants is released into the environment. Cement industry has always been associated with air pollution. From types of pollutants Releases, particulate matter is the most important pollutants of cement plants. In recent years, the cement plant located in the south of Tehran, is one of the most polluting industries in our country and is numbered one of the most important cause of air pollution in the region.

Material and Methodology
From the first steps for the control and reduction of air pollutants emissions, is specified and detected their distribution. Air emissions modeling studies, provide possibility to get useful information for strategies implementation for air pollution controlling in the future. Pollutants dispersion modeling in a variety of emission sources, weather conditions, and pollution source location maybe capable to provide the desired output for the planning and management of reduction and control the emissions pollutants. Air quality models are widely used in recent several decades and made based on calculations by the computer.
Computer modeling of air pollution dispersion model was used by AERMOD. AERMOD is a steady dispersion state model and for determination the concentration of different pollutants in urban and rural areas, smooth and rough, and the high level of emissions from point sources, the volume and variety of surface materials can be used. The model images distribute and dispersion of pollutants from the source to the receiver. So in this studying, model was used to simulate the particle dispersion and was used to evaluate the emission effects of various industrial sources, The model is applied for evaluating the emission effects from various industrial sources at distances less than 50 km and has been investigated zoning the radius of dispersion of pollutants. AERMOD model uses two preprocessor. AERMET is a meteorological preprocessor and another named AERMAP which is a geologist preprocessor. AERMET preprocessor processes meteorological data and estimates atmospheric boundary layer parameters for use in the model and AERMAP preprocessor analyzes the regional topographic information.

Figure 1. Data preparation process in AERMOD by preprocessing of AREMET

Finally the model using result of these two processors and supplemental information about the sources of emission and acceptor networks done the calculations and presents final results.

Figure 2. General stracture of AERMOD model
Results and discussion
In this study, The basic data considering measurement reports and output aerosol sampling of the stack and weather data from the meteorological organization (In this research was used climate variables such: temperature, relative humidity, wind direction and intensity, in daily scale for Doshan-tappe weather station on 2010) And the studied plant was obtained . In the next step the pollutants sources location map separately was prepared the resolution in the factory location(onsite) and nearest weather station. Then Distribution of particulate emissions for time average of 1, 3, 8 and 24 hours And a period of one month and seasonal for both summer and winter conditions by entering the data related to each stack AERMOD model with Emission rate in grams per second by calculating the flow on the scale of Micrograms to the seconds and multiply by that values for each output aerosol concentration in micrograms per cubic meter, were done.as a matter of fact emissions variables and pollutants properties (chimney height, speed and exhaust gas temperature, the volume of pollutants, etc.) of the cement plant, according to a quarterly sample results were received from 12 sources of pollutants that were all kinds of chimneys. Finding of air pollution dispersion modeling shows that the greatest impact of suspended particles at a distance of 1 to 5 km from the emission source occurs. Particles in the summer entry to Tehran from the plant origin had increased further, and covered to 15km of the source.
in this study, simulation was done for 2 meters height or surface to breathe. Simulated altitude is assumed in a flat mode.by referencing to the results of modeling, in both summer and winter periods, for the hourly average are highest value. In both hourly cases the prevailing point is emission source Eastward. In the summer case, due to heat and the more intensity wind blowing, the more range of area around the plant is located within the dispersion of pollutants. Dominant point of factory pollutants spread is South East and East. The concentration because of the high density of suspensor solid Particles than air, decreases more rapidly with increasing distance from the stack. After a long gap, pollutants dispersion to surrounding is caused to reduce its concentration. As it is known, the concentration minimum respectively was recorded at monthly and seasonal averages and particle volume maximum is occurred in hourly average especially on the one-hour. So in the meantime, a considerable difference was seen in levels of particulate pollutant concentrations.

Conclusion
So considering the concentration of particles Standard in Iran and EPA, is observed that result for the Model output is multiplier than Standard rate. And in the hourly and daily measures in the vicinity of the emission source and a factory space, particle size is high.It is proposed cement plant use hybrid filters in their product lines due to significantly reducing its dust.