Evaluation of the distribution of exhaust air pollution from the chimneys of Tabriz Oil Refinery using AERMOD model

Introduction
Controlling industrial pollution sources in order to protect the environment is one of the management strategies in the path of achieving sustainable development, which requires predicting the concentration of pollutants in a specific radius of the chimney and mathematical models can be similar. Air pollution is one of the most important environmental problems in industrial areas and its release from the chimney and its distribution in the atmosphere of any area causes serious damage to the ecosystem of adjacent lands. In point pollution sources such as chimneys of industries and refineries, the spread of pollutants depends on factors such as physicochemical properties of the emitted material, chimney characteristics, meteorological conditions and surface topology.
Materials and methods
In the present study, in order to achieve this approach in the middle mountain plain of Tabriz, the concentration of pollutants emitted from 20 chimneys of Tabriz oil refinery with AERMOD model for a radius of 10 km was predicted. In this study, using meteorological data, land use layer, digital elevation model and chimney characteristics, distribution and concentration of pollutants from the chimneys of Tabriz oil refinery including SO2, NO2, CO and PM2.5 was predicted using the AERMOD model. The AERMOD model is a permanent state distribution model that can be used to determine the concentration of various pollutants in urban and suburban areas. The AERMOD model has two modules including AERMET and AERMAP. The AERMET module is related to the preparation of meteorological and land use data files and the AERMAP module is related to the characteristics of the chimney, pollutants and the digital elevation model. AERMET module data include wind direction and speed, cloud cover, relative humidity and surface air temperature (2 meters above the ground) in a period of one hour, which is in the range of meteorological data of Tabriz Synoptic Station in the interval Estimated time from 2010 to 2020. Using the information provided in the two modules, the distribution of pollutants from the chimneys were calculated using the AERMOD model.
Results and discussion
Annual wind rose plot showed that the dominant wind is from the east and the first-degree wind is from the west. The results of the model prediction showed that the concentration of CO 8h was 0.5 to 20 ug/m³; The concentrations of SO₂ and NO₂ 1h were between 5 and 100 ug/m³, and the concentration of PM_2.5 24h was between 0.5 and 10 ug/m³, which were less than standard emit. East winds transfer pollutants to the northern of the Sahand, southwest of the oil refinery, and accumulate at altitudes of less than 1500 meters. The highest concentration of atmospheric pollutants is in Kheljan city in the southwest of Tabriz oil refinery and prevailing winds have caused the pollutants to move away from Tabriz plain and not have much impact on the environmental ecosystem of Tabriz plain. Pollutants under the influence of prevailing winds, have accumulated in the northern foothills of Sahand and in the southwestern part of Tabriz oil refinery and their maximum limit is in the range of 1450 to 1500 meters, but from this level (1500 m altitude) onwards, as the altitude of the place increases, the concentration of air pollutants decreases. Due to the establishment of the boundary layer, the maximum concentration of air pollutants is at an altitude of 1450 to 1500 meters in the southern foothills, from which the concentration of gases and suspended particles from the chimney is reduced.
Conclusion
In the mid-mountain plain of Tabriz, the concentration of pollutants leaving the chimneys of the oil refinery is less than the standard limit and does not have much effect on various ecologies and ecosystems. Due to the presence of prevailing east winds, the maximum concentration of gaseous pollutants and particulate matter in the northern foothills of Sahand and in the ambient air of Khaljan urban settlement and the wind has caused pollutants from the city of Tabriz, which is located east of the oil refinery. It is moving away and flowing to the southern mountains, and in the metropolis of Tabriz, these pollutants are very low.