epc_fa2011_lecture_9 - Air Pollution Air pollution means...

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Unformatted text preview: Air Pollution -- Air pollution means the presence of contaminants within the atmosphere at concentration detrimental to health or of a nuisance nature (such as SO2 and radon) -- It can occur either naturally or as a result of anthropogenic emissions. -- Historically, urbanization/industrialization had been the main cause of air pollution episodes. Increase in population and housing density Increased heating/power need Greater amount of fossil fuel consumption (coal, oil for heating, transportation, electricity) Increase in emission from fossil fuel combustion resulting in high atmospheric concentration. 1 Air Pollution Episodes - Historical Context -- 1 1800’s -- Pollution episodes started getting more severe than previous ages (rapid industrialization and particularly urbanization in U.S. occurs) 1900’s -- Magnitude for each episode increases exponentially -- Pollutant episodes become quite severe [due to urban population concentration] resulting in widespread illness and death Meuse Valley, Belgium, 1930 - 63 deaths and 8000 illness (due to intense smog) Donora, PA, 1948 - 17 deaths and 6000 illness (due to SO2 with particulates from steel and zinc plants) London, England, 1952 - 4,000 deaths (smog in form of SO2 with particulates from household coal burning) Mid-Sixties - New York city, particularly bad episodes (again, due to SO2 with particulates from fossil fuel) 2 Air Pollution Episodes - Historical Context -- 2 Current -- Life threatening episodes have decreased due to improvement in emissions control and preventive measures -- Cases of dispersive air pollution [from spatially distributed sources/nonpoint-source such as automobile exhausts] far exceed traditional point-source [spatially static source such as factory stacks] air pollution 3 Major Air Pollutants -- 1 1) Particulates (TSP = Total Suspended Particulate) -- Small particles (less than 2 µm) that penetrate both URT (Upper Respiratory Tract) and LRT (Lower Respiratory Tract), settle slowly to bronchi/alveoli and damage lungs. 4 Major Air Pollutants -- 2 2) Hydrocarbon (HC) -- Associated with fossil fuels, petroleum products such as gasoline, composed of H and C atoms. -- PAHs (polynuclear aromatic HC), PCBs (polychlorinated biphenyls), Pesticide, dioxins -- all categorized as carcinogenic. 3) Carbon Monoxide (CO) -- Associated with incomplete oxidation [=combustion] of organic carbon, largely from automobile. -- Form Carboxylhemoglobin (COHb) in blood in high concentration which will deprive the blood of oxygen. (lethal in a few minutes at concentration exceeding 5,000 ppm -- carbon monoxide poisoning). 5 Major Air Pollutants -- 3 4) Ozone (O3) -- Formed by reaction of hydrocarbons and nitrous oxides (NOx). Respiratory irritant. 5) Nitrogen Oxides (NOx) -- Formed at high temperatures from transportation, mainly from automobile engine combustion, and stationary sources such as coal-fired power plants, factory furnace, and home furnaces. (Common brown NOx pollution on the horizon on a late afternoon) 6 Major Air Pollutants -- 4 6) Sulfur Oxides (SOx) -- Consist of Sulfur dioxide (SO2), Sulfur trioxide (SO3), their acids, and salts of their acids. -- Particularly, SO2 can be absorbed in mucous membranes of the URT -- can easily cause chronic bronchitis. -- Largely due to combustion of high sulfur coal from coalfired power plants and factories. 7) Lead (Pb) -- High concentration causes a brain and nerve damages. -- Plant/Vegetation damage can result from high concentrations of lead particulate in the air (i.e., chronically sick/lethargic trees in the urban areas). 7 Major Air Pollutants -- 5 8) Acid Deposition (Acid Rain) -- Largely the result of SOx (Sulfur dioxide, SO2 + Sulfur trioxide, SO3) releases to the atmosphere. a) During combustion process S + O 2 → SO 2 b) Sulfur dioxide reacts in the air with oxygen to form Sulfur trioxide SO 2 + c) Formation of sulfurous acid and sulfuric acid with available atmospheric moisture SO 2 + H 2 O → H 2 SO 3 1 O 2 → SO 3 2 SO 3 + H 2 O → H 2 SO 4 d) These acids are swept from the air by precipitation or deposited in particulate form. e) If the amount of acids exceeds natural carbonate buffer capacity, water becomes acidic – aquatic ecosystem will suffer and start dying off. 8 Major Air Pollutants -- 5 9) Nitrous Oxides (NOx) and Ozone -- Largest source NOx is the natural decay of organic matter (anaerobically). -- Largest anthropogenic sources of NOx are transportation and fuel combustion from stationary sources. -- Elevated levels of NOx in urban areas are primarily due to transportation. -- For example, EDF (Environmental Defense Fund) report contends upto 50% of eutrophication-causing nitrogen influx to the Chesapeake Bay originated from transportation/automobile exhaust from surrounding high-density, metropolitan urban areas (including the Hampton Roads, of course). 9 Major Air Pollutants -- 6 Quick Recap 1) 2) 3) 4) 5) 6) 7) 8) 9) Particulates (TSP = Total Suspended Particulate) Hydrocarbon (HC) Carbon Monoxide (CO) Ozone (O3) Nitrous Oxides (NOx) Sulfur Oxides (SOx) Lead (Pb) Acid Deposition (Acid Rain) Nitrous Oxides (NOx) and Ozone 10 Photochemical Reactions (Smog) -- 1 a) Small amount of atmospheric NO2 can trigger subsequent reactions called NO2 photolytic cycle. NO 2 + photon energy absorbed → NO + O b) Atomic oxygen liberated from NO2 photolytic cycle reacts with atmospheric molecular O2, produce ozone O + O2 + M → O3 + M where M is a third molecule (usually O2 or N2 since they’re abundant in the atmosphere) that absorbs the excess energy from the reaction. Without M, O3 will possess too much energy to stay stable, and will simply dissociate back to O and O2. 11 Photochemical Reactions (Smog) -- 2 c) Ozone subsequently reacts with atmospheric NO to regenerate NO2 and molecular O2, thus completing the cycle. Thus NO 2 + O 2 ⇔ NO + O 3 Similarly for NO3 and HC, NO 3 + O 2 ⇔ NO 2 + O 3 NO x + hydrocarbon → O 3 -- NO2 is a lung irritant (LRT, especially in alveolar sac and bronchiole). Long term exposure might cause increased respiratory illness in a population. -- O3 and PAN (peroxyacetyl nitrate) formed by reaction with hydrocarbons can cause lung distress and impair vegetation growth -- "visible air pollution phenomena from public's point of view." 12 Units of Measure (= Concentration) -- Normally µg per cubic meter (µg/m3) at 0°C and 101.325 kPa -- parts per million (ppm) is also commonly used -- Conversion from µg/m3 to ppm Mass of pollutant( μg) ppm = MW Temp (K) 101.325 kPa × 273 Measure pressure in kPa L 1 m 3 × 1000 3 m × 22.414× 13 National Ambient Air Quality Standard (NAAQS) - 1970 -- National Ambient Air Quality Standard (NAAQS) was proposed by EPA on July, 1997. NAAQS was based on the Clean Air Act (CAA) of 1970. -- Primary Standard was established to protect human health with an adequate margin of safety. 14 Greenhouse Effect -- Short wavelength radiation (less than 0.32 µm) from the sun is absorbed as heat energy at earth ground surface. -- Some portion of heat energy is emitted back from earth surface to space as a long wavelength radiation (0.33 and 0.4 µm). -- Water vapor, CO2, other gases such as methane and NOx (Nitrous oxide) , CFC-11/12 (Chlorofluorocarbon) in atmosphere will trap and strongly absorb this earth surface-reflected long wavelength radiation. -- In >> Out, getting hotter, I.e., Greenhouse. Short wavelength emitted to earth reflected Sun absorbed atmosphere Earth Particles, gases, moisture can reflect radiation Long wavelength radiated back to space by earth Short wavelength reflected at surface 15 Composition of Atmosphere Troposphere - adjacent to earth surface, where weather occurs, most pollutants accumulate. Troposphere starts at the Earth's surface and extends 8 to 14.5 kilometers high (5 to 9 miles). Stratosphere - Stratosphere starts just above the troposphere and extends to 50 kilometers (31 miles) high. - The ozone layer, which absorbs and scatters the solar UV radiation, is in this layer. 16 Atmospheric Stability Related to Heating -- Atmospheric stability is about the movement of warm air parcels (since warm air is less dense than surrounding colder air, i.e., lighter than surrounding air). -- A specific parcel of air with a temperature higher than surrounding ambient air will keep on rising until it reaches a height at which specific parcel of air's temperature and density equal those of surrounding atmosphere. -- As the air parcel rises, it expands due to lower pressure. Subsequently its temperature decreases and becomes lighter and cooler due to expansion. -- Significance of this "air parcel" movement is that "air parcel" will carry and deposit air pollutant(s). In other words, "air parcel" is a vehicle for possible pollutant transports, and is the key to understand air pollution phenomena. 17 Ambient Lapse Rate -- Lapse Rate represents the rate of the temperature changes vertically (with height) in the atmosphere. -- The rate can be determined for a particular place at a particular time by sending up a balloon equipped with thermometer. The balloon moves through the air and the temperature gradient of ambient air, which the rising balloon measures, is called ambient lapse rate (also known as environmental lapse rate or prevailing lapse rate). -- Dry adiabatic lapse rate, Γ (=gamma) represents the rate of decrease in temperature in the air parcel, i.e., max. rate of cooling only due to expansion of air parcel. Height Above Earth’s surface Ambient Lapse rate Temperature 18 Stability vs. Lapse Rate Relationship -- 1 -- The tendency of the atmosphere to resist or enhance vertical motion is called as stability. It is related to both wind speed and the change of air temperature with height (= lapse rate). -- For example, if atmosphere is stable, then not much air movement, and subsequently less pollutant transport (i.e., being dispersed to larger area and contaminate more) would occur. Stable High air pollution potential Unstable Low air pollution potential 19 Stability vs. Lapse Rate Relationship -- 2 1) Unstable Atmosphere Unstable Atmosphere Lifted air Parcel rising Through atmosphere Height Above Earth’s surface Ambient Lapse rate (Superadiabatic) Temperature -- If the ambient lapse rate < dry adiabatic lapse rate (i.e., less temperature loss vertically than the temperature loss due to expansion of the air parcel), the “still-warm” parcel of air lifted into atmosphere will continue to rise through the atmosphere. -- Unstable atmosphere (i.e., stability of atmosphere keeps changing due to movement of air parcels) is favorable to dispersing of pollutants. (i.e., more mixing, more dispersion and more dilution) less likely causes acute air pollution problems) 20 Stability vs. Lapse Rate Relationship -- 3 2) Stable Atmosphere Stable Atmosphere Height Above Earth’s surface Ambient Lapse rate (Subadiabatic) Lifted air parcel (adiabatic cooling) Temperature -- Ambient lapse rate is greater than dry adiabatic lapse rate. -- The lifted air parcel is more dense, much cooler than surrounding atmosphere. It results in sinking back. -- Stable atmosphere keeps pollutants closer to surface. (i.e., pollutants are stuck near the ground level, and don't go anywhere) more likely causes air pollution problems 21 Quick Recap 1) National Ambient Air Quality Standard (NAAQS) 2) Greenhouse Effect – Short wavelength radiations are in, but less amount of Long wavelength radiations are getting out. 3) Ambient Lapse Rate represents the rate of the temperature changes vertically (with height) in the atmosphere. 4) Dry Adiabatic Lapse Rate represents the rate of decrease in temperature, i.e., max. rate of cooling due to expansion of air parcel. 5) Stable atmosphere is more likely have air pollution problems. 22 Effects of Pressure on Contaminant Dispersion -- Ambient Lapse Rate represents the rate of the temperature changes with height in the atmosphere. -- Dry Adiabatic Lapse Rate (Γ) represents the rate of decrease in temperature, i.e., max. rate of cooling due to expansion of air parcel. -- By comparing ambient lapse rate to the adiabatic lapse rate, it is possible to predict what will happen to gases emitted from a stack. -- Shape of smoke trail or plume from a tall stack located on flat terrain will depend on the stability of the atmosphere. -- Depending on stability of the atmosphere, several types of plume are possible; • • • • Looping plume Coning plume Lofting plume Trapping plume • Neutral plume • Fanning plume • Fumigation plume 23 Shape of Plume as F(Stability) -- 1 1) Looping plume (Superadiabatic condition) -- Highly unstable atmosphere (= strong lapse condition, superadiabatic), and pollutants in warmer air parcel will rise and disperse very easily. -- High mixing rate, i.e., wind may carry the plume down to to the ground before dispersion is complete. -- Occurs in clear days with light wind. 24 Shape of Plume as F(Stability) -- 2 2) Neutral plume -- Ambient lapse rate ≈ dry adiabatic lapse rate (=Neutral atmospheric condition). -- The plume rises directly to the atmosphere until it reaches to air layer with a similar density to that of plume itself. (=Neutral) -- Occurs during calm days 25 Shape of Plume as F(Stability) -- 3 3) Coning plume (Subadiabatic condition) -- Ambient lapse rate >> Dry adiabatic lapse rate (=Subdiabatic atmospheric condition). -- Plume cools down quicker than surrounding air during transit/rise (=Subdiabatic), and the plume cannot rise, i.e., “sinking back.” (downward buoyancy force pushes the displaced plume earthward) Resulting in plumes that are coning. -- Limited vertical mixing, and the potential/problem of air pollution in the area increases. -- This plume tends to cone when wind velocity greater than 20 mile/hr and when cloud cover blocks solar radiation by day and terrestrial radiation by night. (= at night and/or when 26 it’s cloudy) Shape of Plume as F(Stability) -- 4 4) Fanning plume -- Ambient lapse rate is negative (=inversion or temperature increase with elevation), the dispersion of stack gas is minimal due to lack of turbulence. -- Plume spreads horizontally with little vertical mixing due to inversion (=fanning) -- Visible from miles away in flat terrain. 27 Shape of Plume as F(Stability) -- 5 5) Lofting plume -- When inversion exists below the source/plume and unstable layer lies above the plume, the plume will disperse aloft but not below. -- This is a desirable situation since the pollutants are dispersed without contributing any significant ground-level conc. -- Lofting conditions prevail in the lake afternoon and early evening under clear skies. 28 Shape of Plume as F(Stability) -- 6 6) Fumigation plume -- Inverse of lofting condition -- Occurs when a stable layer of air lies a short distance above the release point of the plume and an unstable air layer lies below the plume. -- Inversion layer occurs at some point above stack height, and literally blocking any upward vertical movement of air pollutants. -- Can cause high ground concentration of air contaminants 29 Shape of Plume as F(Stability) -- 7 7) Trapping plume -- Occurs when an inversion exists both below and above the stack height. (=sandwiched) -- Results in a coning of plume between inversion layer boundaries. -- Trapping plume only lasts relatively short time period, and hardly persisting. 30 Dispersion -- Terrain Effects -- 1 Heat Island -- Results from “mass” materials such as concrete structures, asphalt, etc. that absorbs and reradiates heat at a greater rate than surrounding area. -- Large industrial complexes, small to large cities, i.e., where "concrete jungle" is. (=hotter in city core in summer) -- Atmospheric stability will be lower over the area of heat islands. (=better dispersion of pollutants) 31 Dispersion -- Terrain Effects -- 2 Land/Sea Breezes -- A strong local circulation pattern may develop across the shoreline of large water bodies. -- During the night, the land mass dissipates heat energy more rapidly than the water body. Cooler air over the land mass flows toward the water body due to density gradient (=Land breeze). -- In the morning, the land mass absorbs heat energy more rapidly than the water body. Cooler air over the water body flows toward the land due to density gradient (=Sea breeze). -- Plumes developed near the shoreline will form a fanning plume, progresses into a fumigation plume several km in land. 32 Atmospheric Dispersion of Plumes -- Plume expands and mixes with ambient atmosphere, and contaminants eventually disperse toward the ground. -- Plume rise affected by; a) Upward inertia of gas stream (exit velocity of gas and mass) b) Buoyancy of gas stream Plume rise (ΔH) + Physical stack height (h) = Effective stack height (H) -- Factors affecting dispersion of contaminants are; a) Effective stack height b) Downward distance (to a ground level receptor) c) Wind speed and direction (affect rise and rate of mixing) d) Stability of ambient atmosphere 33 Gaussian Dispersion Modeling Concept -- Gaussian dispersion modeling technique is a mathematical representation of meteorological transport and dispersion process for given contaminant(s). -- Numerical calculations yield estimates of concentration of the particular pollutant for specific locations and times (spatially and temporally dependent) -- Based on Normal Probability Distribution concept f (X ) = Normal PDF ⎡ − (x − μ )2 ⎤ 1 exp ⎢ ⎥ 2 σ 2π ⎦ ⎣ 2σ 0.6826 0.95 0.997 -3σ -2σ -1σ μ 1σ 2σ Empirical Rule μ ± 1σ = 0.6826 ≈ 68% μ ± 2σ = 0.9545 ≈ 95% μ ± 3σ = 0.9973 ≈ 99.7% 3σ 34 Point Source (PS) Gaussian Dispersion Model -- 1 Assumptions 1) At discharged layer, atmospheric stability is uniform. 2) Random turbulent diffusion of contaminants in the gas stream; -- both vertical and horizontal directions. -- can be represented by a normal probability approximation, i.e., the distribution of pollutant concentration in the plume would follow the standard normal probability distribution. 3) Gas stream is released into atmosphere at a distance above ground level that is equal to stack height (h) + plume rise (ΔH) = Effective stack height (H). ΔH 4) Degree of dilution of the plume is inversely proportional to wind speed (u) 35 Point Source (PS) Gaussian Dispersion Model -- 2 -- Normally, drifting in the plume in x-direction is so much faster than y-direction, so that the transport can be approximated solely by convection. -- Also, since plume propagation is very fast in a short duration, the transport process can be considered steady-state. -- With convective and steady-state approximation, downstream average concentration of plume, cd can be expressed as u Exx W y Ax Ax x ⎛ u⎞ c d = exp⎜ − ⎜ E x⎟ ⎟ xx ⎠ ⎝ ≈ W uA x Ax= Traverse cross-sectional area of the plume at downstream distance x from the origin at x=0 At x=0 Ax = a cross-sectional area of stack At x>0 Ax expand laterally due to dispersion u= Wind speed Exx= Dispersion coefficient applicable to downstream direction W= Pollutant(s) loading from the stack 36 Point Source (PS) Gaussian Dispersion Model -- 3 -- Extent of Ax at distance x from the stack can be computed from the variance of the distance, σ2 from the plume centerline, i.e., σ is treated as a radius of Ax. -- Now, using the Normal probability distribution, one standard deviation distance from the sample mean (=the plume centerline) equals to 68.26% of the area of the cross-sectional area. Ax Ax -- Also, σ2 represents the population's variance. When used in a case-specific computation, σ2 can be substituted with s2, which is a sample's variance distance from the plume centerline. Ax = ΔH Ax π σ2 0.6826 = ⎛u c d = exp⎜ − ⎜E xx ⎝ π σ yσ z 0.6826 ≈ π s ysz 0.6826 ⎞ W 0.6826W x⎟ ≈ ⎟ uA = uπ s s x yz ⎠ 37 Point Source (PS) Gaussian Dispersion Model -- 4 -- For turbulent flow in pipes which emulates a dispersive flow, the ratio of the average velocity to the maximum velocity ranges from 0.5 to 0.82, and gives an average velocity ratio of 0.66. -- Considering the plume as a turbulent pipe and approximating the ratio of the average concentration of plume to the maximum concentration at the center of plume as 0.66; Ax Ax 0.6826W = 0.66 c d uπ s y s z ⇒ cd = 1.03W uπ s y s z -- With cd known, and assuming a steadystate transport process, the downwind concentration at ground level, c at (x,y) can be expressed by Turner’s Eq.; 2 ΔH Ax 2 ⎛ y⎞ 1.03W ⎟ exp⎛ − H ⎞ ⎜ ⎟ c= exp⎜ − ⎜ ⎜ u π s ysz 2 sy ⎟ 2 sz ⎟ ⎝ ⎠ ⎝ ⎠ 2⎞ 2⎞ ⎛ ⎛ ⎛y⎞⎟ ⎜ W ⎟ exp⎜ − 0.5 ⎛ H ⎞ ⎟ ⎟ ⎜ ≈ exp⎜ − 0.5 ⎜ ⎟ ⎜s ⎟ ⎟ ⎜ ⎜ sy ⎟ ⎟ u π s ysz ⎜ ⎝ z⎠ ⎠ ⎝ ⎠⎠ ⎝ ⎝ 38 Point Source (PS) Gaussian Dispersion Model -- 5 IMPORTANT RATIONALE behind WHY THIS? The idea of using the normal probability distribution for estimating the extent of Ax [instead of using some empirical equations] is a) Every case/stack situation is different, and estimating case-specific empirical equation(s) for computing Ax is not practical, at the same time doing such does not guarantee the accuracy. u Exx W Ax Ax b) Normal probability distribution is based on a bell-shaped curve of Cumulative probability that represents a general trend observable, and is ideal to represent the likelihood of natural random phenomena in a quantitative manner. (such as turbulent mixing of pollutant in a hot/warm gaseous plume!) x y 39 Point Source (PS) Gaussian Dispersion Model Calculation Procedure -- 1 1) Horizontal (sy) and vertical (sz) Plume standard deviations can be either (i) interpolated from charts (Figures 7-22 and 7-23, page 592) if the atmospheric stability type and location x at downwind direction from the stack are known or (ii) calculated using Martin's curve-fit equations s y (m ) = a[x (km )]0.894 s z (m ) = c[x (km )]d + f a, c, d and f are Martin's curve-fit coefficients. (you will read them off from the table based on Stability Type) Keep in mind that 'x' in Martin's equations above are in km, and resulting syand sz are in m. 40 Point Source (PS) Gaussian Dispersion Model Calculation Procedure -- 2 Calculation Procedures for sy and sz in Martin's curve-fit equations a) Find a atmospheric Stability Type based on the surface wind speed at the stack, and a solar radiation condition at a given time using following table. 41 Point Source (PS) Gaussian Dispersion Model Calculation Procedure -- 3 Calculation Procedures for sy and sz in Martin's curve-fit equations – Cont.d b) With the atmospheric stability type from step a), find corresponding Martin's curve-fit coefficients and calculate sy and sz c) s y (m ) = a[x (km )]0.894 s z (m ) = c[x (km )]d + f Keep in mind that 'x' in Martin's equations above are in in km, and resulting and sz sz are in . . are km, and resulting sy syand are in m m Be sure to use correct Units!!! 42 Point Source (PS) Gaussian Dispersion Model Calculation Procedure -- 4 2) Find Effective stack height, H = stack height (h) + plume rise (ΔH). Normally, stack height is known, and ΔH can be estimated using Holland's empirical equation ΔH = ⎛ Ts − Ta ⎞ ⎤ vsd ⎡ −2 ⎢1.5 + 2.68 × 10 × p⎜ ⎟ ⎜ T ⎟d⎥ u⎢ s ⎠⎥ ⎝ ⎦ ⎣ Where vs = Stack exit velocity, m/sec d = Diameter of the stack opening, m u = Wind speed, m/sec p = Atmospheric pressure, kPa Ts = Stack temperature, K Ta = Ambient air temperature, K Be sure to use correct Units!!! 43 Point Source (PS) Gaussian Dispersion Model Calculation Procedure -- 5 3) Finally, the downwind concentration at ground level, c at (x,y) can be calculated by using Turner’s Equation ⎛ y 1.03W c= exp⎜ − ⎜ u π s ysz 2 sy ⎝ ≈ Ax 2 ⎞ ⎟ exp⎛ − H ⎜ ⎟ ⎜ 2 sz ⎝ ⎠ ⎞ ⎟ ⎟ ⎠ 2 2 2⎞ ⎛ ⎛ ⎛y⎞⎞ ⎜ W ⎟ ⎟ exp⎜ − 0.5 ⎛ H ⎞ ⎟ ⎜ ⎟ exp⎜ − 0.5 ⎜ ⎜s ⎟ ⎟ ⎜ ⎜ sy ⎟ ⎟ u π s ysz ⎜ ⎝ z⎠ ⎠ ⎝ ⎠⎟ ⎝ ⎝ ⎠ Where Ax ΔH Ax c = Conc. at ground level at (x,y), g/m3 W = Emission/Loading rate of pollutant, g/sec u = Wind speed, m/sec sy and sz = Plume std. dev., m y and H = Distance, m Be sure to use correct Units!!! 44 Quick Recap 1) Shape of smoke trail or plume from a tall stack located on flat terrain will depend on the Stability of the atmosphere. 2) Stable atmosphere is more likely to have air pollution problems. (stuck and pollutants do not move/disperse away) 3) Stability of the atmosphere can be described by comparing Ambient Lapse Rate and Dry Adiabatic Lapse Rate. 4) Coning and Fumigation plumes are the ones that would cause air pollution episodes at ground levels! 5) Gaussian Dispersion Model is based on Normal Probability Distribution, and is to estimate the likelihood of downwind conc. of pollutants at the ground level at (x,y). 45 ...
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