AERMOD Project Mentor
Environmentalconservation is a primary responsibility of every nation andindividual as the nature of the environment is the determinant of allother economic, climatic, social, and future of the earth. Due to thehigh importance that environment holds, governments formulatepolicies and laws that regulate the actions of various stakeholdersconcerning environmental conservation. Air pollution is one of themajor issues that regulators strive to control since it has the worstconsequences on the ecosystem. Consequently, the United StatesEnvironmental Protection Agency, designed a model that measures theemission of air pollutants from the different areas (Guerra,2014).AERMOD is an atmospheric dispersion model with three integratedsystems. It is a legal requirement to estimate the AERMOD data beforeestablishing any process that emits air pollutants and compare itwith the National Ambient Air Quality Standards. Therefore, theessays seek to evaluate whether a biomass station should be builtafter the analysis of its AERMOD data.
Asstated earlier, American Meteorological Society/U.S. EnvironmentalProtection Agency Regulatory Modeling System (AERMOD) is anatmospheric dispersion model with three integrated systems. One ofthe systems ensures a steady-state diffusion model for short-range(up to 50 kilometers) dispersion of air pollutants from staticindustries. Secondly, it has a meteorological data processor known asAERMET that captures meteorological data and air surroundings, andthen estimates the atmospheric parameters required for the dispersionmodel. Finally, it has the AERMAP that provides physical data andrelationship between the demographics features and diffusionbehaviors of air pollutants. AERMOD model operates through asimulation process whereby it simulates the possible shapes of themovement of air currents at the ground or elevated, at buoyant ornon-buoyant, and at one or more pollutant emissions.
Thematerials and methods used when applying AERMOD encompass all therequirements and key elements that are needed for a successful andaccurate analysis. Concerning the data used, AERMOD uses two sets ofdata surface data and vertical profile, both recorded hourly.Surface data includes all the relevant air information that arehorizontal or on the surface of the earth. They include the sensibleheat flux, convective velocity, the friction velocity, verticaltemperature for a maximum height of 500 meters above the ground.Other variables in the surface are the planetary boundary layer, themechanical boundary layer extent, the surface roughness, theconvective boundary layer size, the wind speed and direction,temperature, and the anemometer and thermometer heights (Guerra,2014).Besides, most of the surface information is captured through theAERMAP.
Inaddition to the surface data, the vertical data is also crucial forAERMOD analysis. The data required include the vertical profile areafor different elevations above the ground, the wind speed, the sizeof the elevation, the wind direction, temperature, and the standarddeviations of wind speed and wind direction. Nevertheless, the mostcrucial data when undertaking AERMOD simulation is the wind directionand the wind speed. Apart from the data, AERMOD simulation usessoftware and computer applications, which enable the simulator toundertake the process and make relevant decisions. One of thesoftware used is the WindRosePRO3 software that allows the user todevelop wind roses directly for the surface meteorological data.Other software mentioned earlier is the AERMAP that provides the dataon the relationship between physical terrain and air pollutantsbehavior, and the AERMET that processes the surface meteorologicaldata.
Inputparameters include all the variables that are used in the simulationto make the analysis and conclusions. In the AERMOD simulation, theinput parameters required include the atmospheric turbulence. Inthis regard, AERMOD uses continuous vertical profiles of both thevertical and horizontal turbulence. Turbulence may be defined as theunsteady or violent movement of air currents within the region of thestudy of analysis. Additionally, AERMOD uses the dispersion underconvective conditions parameters that is, the vertical dispersionunder convective conditions. Within this parameter, the plume of theair pollutant has three vital components the direct plume directedto the ground by the downdraft, the indirect plume captured by theupdraft and pushed to the superior lid and then pushed to the groundby another downdraft. And thirdly, the penetrating plume that passesthe mixing layer and disperses slowly on a stable layer above themixing layer.
Additionally,AERMOD uses the plume buoyancy parameter, which is the ability of theair pollutant plume to float on the surface. The model uses thevalues at stack height, which is the half distance from the finalheight, while under unstable atmospheric conditions. Contrarily,under convective conditions, the model uses random displacementsdata. On the same note, the Monin–Obukhov length is anotherparameter that measures the how buoyancy affects turbulence flows.The theory was defined by Alexander Obukhov to determine the heightat which turbulence is generated by buoyancy than the velocityfriction or wind shear.
Otherparameters used include the speed of friction, which is theresistance force between layers of air currents. The frictionvelocity is the shear force that influences the movement of aircurrents and so is the spread of air pollutant. Additionally, AERMODuses the heat flux data, the rate of at which energy passes throughthe air surface, the vertical temperatures of the air sincetemperature influences the weight and speed of the wind. Finalparameters include the planetary boundary layer, the mechanicalboundary layer extent, the surface roughness, the convective boundarylayer extent, the wind speed and direction, temperature, and theanemometer and thermometer heights.
TheModules of AERMOD
Asmentioned briefly earlier, AERMOD has three major modules thatoperate together to achieve the simulation and provide the requiredinformation. The first module is the steady-state dispersion modelthis measures the distance of up to 50 kilometers that air pollutantcan spread steadily. The second module is the AERMAP, a terrainpreprocessor that provides information between the relationshipbetween the ground and the pattern of air pollution plumes. AERMAPuses gridded terrain data to compute the terrain influence height foreach of the AERMOD receptors. That is, the AERMAP estimates thepollutant impact on flat and elevated terrain, and the informationgathered influences the decision of the location of the air pollutingindustry. The third module is the AERMET, a collection of softwareand programs that accept meteorological data and then processes it toestimate the atmospheric parameters needed for the AERMOD.
Theconstruction of a new biomass combined heat and power station willrequire detailed analysis and AERMOD simulation to estimate thequantity of pollutants emitted. Since the proposed project locationis Dartmouth around the harbor the AEERMAP findings conducted on theproposed site showed that the average wind speed is 5.13 miles persecond and the percentage calm wind is 22.93%. The survey wasconducted for a total of 9526 hours and to ensure that the findingswere accurately evaluated from a large population size. The summaryof the wind speed findings was recorded in the polar graphs attachedin figure A below. Therefore, the data acquired from this initialsurvey shall be integrated into the industry data on the types ofpollutants and the quantity that the industry shall emit. Theinformation of the amount of polluting gasses is acquired from themanufacturing production data that shows the by-products amount.
Thewind rose diagram represented figure B below, illustrates thedirection of the wind. The winds originate from southwest tonortheast, and thus the greatest impact of the pollution is expectedon the north eastern side. Furthermore, most of the wind movestowards the lake, and thus, the resultant impact or effect of thepollution does not affect the residents of the area. Therefore, theindustry has all the qualifications for establishment except for theNational Ambient Air Quality Standard (NAAQS), which is the next stepfor the analysis. The AERMOD simulation of the total amount ofemissions from the new biomass combined heat and power station showedthat the in one hour the total Nitrogen Dioxide (NO2) emitted is 98ppb (parts per billion) while that of Sulfur Dioxide (SO2) is 59ppb(parts per billion. Based on the data above, the project had to besubmitted to the Environmental Protection Agency to undergo furtheranalysis and compliance with the National Ambient Air QualityStandard (NAAQS) (Gulia,2015).The final results of after the second investigation would determinewhether the new biomass combined heat and power station should bebuilt or avoided.
Comparison to National Ambient Air Quality Standard (NAAQS)
National Ambient Air Quality Standards (NAAQS) were established in 1990 under the Clean Air Act. The standards regulate activities that emit dangerous gasses that pollute the air the primary concern of these rules is to control the emission of the main polluting gasses that are harmful to the public health and environment (EPA, 2012). According to the requirements of the Clean Air Act, NAAQS has to types of standards that is, primary and secondary standards. The primary standards are those measures that regulate the emission of gasses that are harmful to the public health. The standards protect the health of sensitive populations such as children, people with asthma and the elderly. The secondary standards, on the other hand, protect the public welfare such as protection against reduced visibility, damage to vegetation, crops, buildings and natural resources.
The standards regulate six major pollutants commonly known as the criteria air pollutants. The gasses include Carbon Monoxide (CO Lead (Pb), Nitrogen Dioxide (NO2), Ozone (O3), Sulfur Dioxide (SO2), and Particle Pollution (PM). According to the standards, Nitrogen Dioxide (NO2) of 100ppb in 1 hour, within the primary standards should be a maximum of 98% of 1-hoiur daily and averaged in three years (EPA, 2012). That is an average of 98ppb per hour for three years. Within the secondary standards, the gas should be a maximum of 53ppb annually. Sulfur Dioxide (SO2), on the other hand, should not exceed 99% of 75ppb of 1 hour daily concentrations, averaged over three years under the primary standards. On the secondary standards, it should be 0.5ppm (parts per million) for three hours, and for more than three years (EPA, 2012).
In comparison with the findings of the AERMOD simulation for the new biomass combined heat and power station, the Nitrogen Dioxide (NO2) emission in the industry is lower that the standards. That is, the plant shall emit 98ppb which corresponds to the primary level of a maximum of 98% of the 100ppb per hour daily. Sulfur Dioxide (SO2) shall be emitted at 59ppb, implying that the amount is lower that the primary standards of a maximum of 99% of 75ppb on 1 hour daily concentrations, averaged for three years. Therefore, under the primary standards of the NAAQS, the new biomass combined heat and power station has met the qualification and should be constructed.
The plant should be constructed because it has met the NAAQS requirements regarding the emission of air pollutants. The analysis above shows that the amount of Nitrogen Dioxide and Sulfur Dioxide emitted is below the requirements, and thus, the plant is not dangerous. Besides, when the level of pollutants is low, it implies that the industry or the government can implement control measures that either recycle the byproducts or channel them to the correct disposal. Furthermore, the plant is a combination of biomass, heat and power station, implying that it is a natural source of energy, which is also a measure for environmental conservation and thus, the plant should be built.
Conclusively, the construction of a new biomass combined heat and power station may result in the emission of dangerous gasses to the environment. Polluted air has massive challenges to the ecosystems and thus must be controlled accordingly. Through AERMOD simulation, various contributors to the spread of air pollutant are analyzed and simulated to establish the significance of the pollution or the spread of the pollutant to the environment. The findings from the AERMOD are then weighed against the National Ambient Air Quality Standards (NAAQS). According to the analysis and findings, the new plant should be constructed since the amount of Sulfur Dioxide and Nitrogen Dioxide emitted is below the standards, implying that they do not have significance impact and can be regulated.
EPA, U. (2012). National Ambient Air Quality Standards (NAAQS). Retrieved 10/07/2013, 2013, from https://www.epa.gov/criteria-air-pollutants/naaqs-table
Guerra, S. A. (2014). Innovative dispersion modeling practices to achieve a reasonable level of conservatism in AERMOD modeling demonstrations. EM Journal, 12, 24-29.
Gulia, S., Kumar, A., & Khare, M. (2015). Performance evaluation of CALPUFF and AERMOD dispersion models for air quality assessment of an industrial complex.
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