The relationship of fly ash light absorption to smoke plume opacity

Measuring the fly ash light absorption for coal-fired boilers with the Integrating Plate Method (IPM) is discussed. It is observed that measurement of the optical properties of fly ash may also be useful for comparison with ambient aerosols to identify the relative contribution of primary particulates to downwind visibility. The IPM technique is defined as comparing the light absorption through a clean nuclepore filter to one with a single layer of aerosol by integrating the scattered light so only absorption is measured. Since the light absorption is a strong function of particle size, careful sizing is required for accurate measurement. Preliminary calibration and fly ash data are reported.     

Reactive plume model: Effect of stack exit conditions on gas phase precursors and sulfate formation

A simple form of a carbon-bond smog mechanism has been introduced into a complete set of plume conservation equations. The conservation expressions for mass, momentum, energy and component species have been solved numerically for typical source and neutral or adiabatic ambient conditions to simulate the homogeneous gas phase chemistry for approximately two hours of travel time downwind from the stack exit. The influence of stack exit conditions including the ratios of momentum-to-buoyancy length l_m/l_b, source-to-ambient velocity R and mixing-to-reaction time τ are demonstrated.It was found that homogeneous processes in the plume near-field do not significantly contribute to the overall conversion of SO₂ to SO²⁻₄. In the far-field maximum sulfate formation rates of 2.3% h⁻¹ were predicted for clear summer noon hours, consistent with plume measurements. Variation of stack exit conditions were found to have little effect on the maximum SO₂ conversion rate or the peak OH radical concentration where local HC/NO_x ratios between 16 and 22 were predicted. Parameter changes resulting in greater ambient entrainment rates, however, were found to shift the development of the radical pool closer to the source and to significantly increase the total molar flux of plume sulfate.     

An experimental verification of a theoretical model for the dispersion of a stack plume heavier than air

Experiments were carried out in a windtunnel to test the theoretical model for the dispersion of a stack plume heavier than air developed by Ooms et al. (1974, First Int. Symp. on Loss Prevention and Safety Promotion in the Process Industries, The Hague). Particular attention was paid to the initial conditions which have to be supplied in order to make model calculations possible. A good agreement between experimental results and model predictions was found for the plume path and the density distribution along the plume axis. The velocity distribution inside the plume was less well predicted.     

Simulation of dispersion of a power plant plume using an adaptive grid algorithm

A new dynamic adaptive grid algorithm has been developed for use in air quality modeling. This algorithm uses a higher order numerical scheme—the piecewise parabolic method (PPM)—for computing advective solution fields; a weight function capable of promoting grid node clustering by moving grid nodes; and a conservative interpolation equation using PPM for redistributing the solution field after movement of grid nodes. Applications of the algorithm to a model problem, in which emissions from a point source disperse through the atmosphere in time, reflect that the algorithm is able to capture not only the regional ozone plume distribution, but also the small-scale plume structure near the source. In contrast, the small-scale plume structure was not captured in the corresponding static grid solution. Performance achieved in model problem simulations indicates that the algorithm has the potential to provide accurate air quality modeling solutions at costs that may be significantly less than those incurred in obtaining equivalent static grid solutions.     

Fugitive emissions opacity determination using the digital opacity compliance system (DOCS)

Maintenance of Department of Defense (DoD) weapon systems, conducting battlefield training exercises as well as meeting military construction and/or demolition schedules, invariably generate fugitive air emissions, many of which are visible. Although there is no codified federal method for quantifying fugitive emissions opacity, many state and local air regulatory agencies have instituted enforceable fugitive emission opacity standards at DoD facilities. The current study focused on comparing the performance of the digital opacity compliance system (DOCS) with U.S. Environment Protection Agency Method 9 (Method 9) certified human observers in quantifying the visible opacity associated with fugitive emissions produced using a commercial fog generator. By systematically repositioning both DOCS cameras and Method 9-certified observers during field testing, differences in method performance as a function of observational locations were documented. At both the 30- and 300-ft off-set distances, opacity levels reported by the DOCS technology and Method 9-certified smoke readers were found to be statistically different at the 99% confidence level. Alternatively, at the 90- and 150-ft off-set distances, results suggested that there was an insignificant difference at the 99% confidence level between the two methods. Comparing the magnitude of the each method's standard deviation suggested that, at the 30-ft off-set distance, the DOCS technology was consistently more precise than Method 9-certified readers regardless of the observer's downwind distance. However, at the 90, 150, and 300-ft off-set distances, method precision seemed to vary as a function of both off-set and downwind distance. The primary factor affecting the consistency in opacity measurements appeared to be the impact of ground-level air turbulence on fog plume dispersion and transport. Field observations demonstrated that localized wind shear played a critical and decisive role in how and to what extent fugitive emissions opacity could be determined, regardless of the method selected.     

Field demonstration of visible opacity photographic systems

The Digital Opacity Compliance System (DOCS) is an innovative method that uses digital imaging technology to quantify visible opacity of stationary sources. DOCS, which has been demonstrated at pilot and full scale as a technically defensible and economically attractive alternative to U.S. Environmental Protection Agency (EPA) Reference Method 9 (Method 9), uses commercial-off-the-shelf (COTS) digital cameras in combination with a user-friendly computer software package to determine opacity. To date, all DOCS field testing has been conducted using two models of digital cameras, notably, Kodak Models DC265 and DC290, both of which are no longer commercially available. To ensure that field-validated digital cameras will be available to future DOCS users, a suite of new digital cameras was evaluated with the opacity determination software including the following: (1) Sony Model Cybershot Model DSC-WI, (2) Nikon Model Coolpix 5200, (3) Fuji Finepix Model E500, and (4) Kodak Model DX6490. Within the opacity range of regulatory interest, that is, 0-40%, the Sony Cybershot Model DSC-WI and Nikon Coolpix Model 5200 digital cameras were found to generate plume photographs of which the DOCS opacity analysis yielded results that were statistically equivalent to the previously field-validated Kodak Model DC290. In contrast, the Fuji Finepix Model E500 generated plume photographs of which the DOCS opacity analysis were, on average, 2.2% less than those generated by the Kodak Model DC290 photographs, a difference that was determined to be statistically significant. Over the same opacity range, photographs taken by the Kodak Model DX6490 yielded DOCS opacity readings that were found to be statistically equivalent to a Method 9-certified transmissometer. Based on the results from the current digital camera validation testing approach, EPA has developed a new camera-based visible opacity measurement method titled "Determination of Visible Emission Opacity from Stationary Sources Using Computer-Based Photographic Analysis Systems." The proposed method is expected to be promulgated after closure of the public comment period.     

Non-empirical closure of the plume equations

A plume model capable of predicting trajectories, dilution, width, and other important plume properties may be developed with very little empirical input, namely, common plume assumptions and the Taylor entrainment hypothesis. The Taylor hypotheses is necessary in cases of little or no current, but, as current increases, it decreases in importance until the point is reached where it may be omitted. In such instances the model may be practically non-empirical. An objective model of this nature is necessary because there is always some doubt that empirical models may be generalized—especially when known data, to which they are fitted, are subject to relatively large uncertainty as plume data are. The resulting model predicts a wide range of plume behavior and, far from being complex, is even easily adapted for use with personal computers.     

Simulation of the evolution of particle size distributions in a vehicle exhaust plume with unconfined dilution by ambient air

Over the past several years, numerous studies have linked ambient concentrations of particulate matter (PM) to adverse health effects, and more recent studies have identified PM size and surface area as important factors in determining the health effects of PM. This study contributes to a better understanding of the evolution of particle size distributions in exhaust plumes with unconfined dilution by ambient air. It combines computational fluid dynamics (CFD) with an aerosol dynamics model to examine the effects of different streamlines in an exhaust plume, ambient particle size distributions, and vehicle and wind speed on the particle size distribution in an exhaust plume. CFD was used to calculate the flow field and gas mixing for unconfined dilution of a vehicle exhaust plume, and the calculated dilution ratios were then used as input to the aerosol dynamics simulation. The results of the study show that vehicle speed affected the particle size distribution of an exhaust plume because increasing vehicle speed caused more rapid dilution and inhibited coagulation. Ambient particle size distributions had an effect on the smaller sized particles (approximately 10 nm range under some conditions) and larger sized particles (>2 microm) of the particle size distribution. The ambient air particle size distribution affects the larger sizes of the exhaust plume because vehicle exhaust typically contains few particles larger than 2 microm. Finally, the location of a streamline in the exhaust plume had little effect on the particle size distribution; the particle size distribution along any streamline at a distance x differed by less than 5% from the particle size distributions along any other streamline at distance x.     

Measuring visual opacity using digital imaging technology

The U.S. Environmental Protection Agency (EPA) Reference Method 9 (Method 9) is the preferred enforcement approach for verifying facility compliance with federal visible opacity standards. Supporters of Method 9 have cited its flexibility and low cost as important technological and economic advantages of the methodology. The Digital Opacity Compliance System (DOCS), an innovative technology that employs digital imaging technology for quantifying visible opacity, has been proposed as a technically defensible and economically competitive alternative to Method 9. Results from the field application of the DOCS at EPA-approved Method 9 smoke schools located in Ogden, UT, Augusta, GA, and Columbus, OH, demonstrated that, under clear sky conditions, the DOCS consistently met the opacity error rate established under Method 9. Application of hypothesis testing on the smoke school data set confirmed that the DOCS was equivalent to Method 9 under clear sky conditions. Under overcast sky conditions, human observers seemed to be more accurate than the DOCS in measuring opacity. However, within the smoke school environment, human observers routinely employ backgrounds other than sky (e.g., trees, telephone poles, billboards) to quantify opacity on overcast days. Under conditions that compel the use of sky as plume background (e.g., emission stacks having heights above the tree line), the DOCS appears to be a more accurate methodology for quantifying opacity than are human observers.     

Integral model of dense gas plume dispersion

The injection of a dense gas stream at ground level into a flowing turbulent atmosphere produces a wide, flat plume that entrains air primarily through its upper surface. A quasi-one-dimensional flow model of an isothermal dense gas plume is developed for the purpose of comparing experiments in wind tunnels and water flumes and field tests in the atmosphere. Comparisons are made for plume width, including the width at the source, and centerline ground plane source gas concentration. All published data are used in this comparison, which cover a factor of about 100 in plume length scale and Reynolds number. Tests conducted by different experimenters were found not to be dynamically similar. Dimensionless model parameters, all of order unity, are selected to give the best agreement among all the experimental data. The dependence of entrainment rate on the plume Richardson number, a key feature of the model, is confirmed in the comparison. The entrainment rate parameter is found to be larger for the field tests than for the laboratory experiments, reflecting the much higher Reynolds number of the former.     

Atmospheric dispersion of a chemically reacting plume

The atmospheric dispersion of a plume of pollutants, undergoing fast enough chemical reactions so that equilibrium is reached, is modelled. The effects of turbulence on the mean concentrations, due to turbulence-chemistry interactions and dispersion, are found by combining the probability density function method and the Gaussian plume model. The results, for a plume of NO and NO₂ in ambient ozone on a sunny day, show that the NO concentration is higher than the value expected for a nonturbulent chemistry model. The effects of temperature fluctuations are shown to be small. The method depends upon the assumption of instantaneous equilibrium and the conditions for this breaking down are pointed out.     

Migration and natural fate of a coal tar creosote plume: 1. Overview and plume development

A volume of sand containing coal tar creosote was emplaced below the water table at CFB Borden to investigate natural attenuation processes for complex biodegradable mixtures. Coal tar creosote is a mixture of more than 200 polycyclic aromatic hydrocarbons, heterocyclic compounds and phenolic compounds. A representative group of seven compounds was selected for detailed study: phenol, m-xylene, naphthalene, phenanthrene, 1-methylnaphthalene, dibenzofuran and carbazole. Movement of groundwater through the source led to the development of a dissolved organic plume, which was studied over a 4-year period. Qualitative plume observations and mass balance calculations indicated two key conclusions: (1) compounds from the same source can display distinctly different patterns of plume development and (2) mass transformation was a major influence on plume behaviour for all observed compounds.     

Chimney plume penetration of the sea-breeze inversion

Data from a study of buoyant plume interaction with the sea-breeze inversion are discussed with the view of testing inversion penetration criteria. While limited in its aims and the quantity of data available, the study is unusual in that observations of all relevant physical quantities are available. Analysis shows that the Briggs (1969) criterion for penetration is too conservative, while the predictions of Briggs (1975) are too optimistic. Predictions by Manins (1979) are supported. The study demonstrates that plumes can partially penetrate an inversion, with some material being mixed downward and some lost to higher levels.     

Sulfur budget of a power plant plume

As part of the Midwest Interstate Sulfur Transformation and Transport (MISTT) study, the summer sulfur budget of the plume of the 2400 MW coal-fired Labadie power plant near St. Louis, Missouri is assessed via aircraft data, ground monitoring network data and a two-box model. The paniculate sulfur (S_p) formation rate is obtained from three-dimensional plume mapping combined with a high time-resolution S_p sampling technique. During noon hours the SO₂ conversion rate is found to be 1–4% per hour, compared to night rates below 0.5% per hour. Plume excess light scattering coefficient (b_scat) and excess S_p correlated well (r = 0.87), indicating most S_p is formed in the light-scattering size range.During daytime the well-mixed plume is transported at 5ms⁻¹ on the average; at night the July average wind speed at plume height is 12ms⁻¹ due to the low-level jet The nocturnal plume is less than 100 m thick at 400 m above ground and is decoupled from the surface until morning. Ground monitoring data from the Regional Air Pollution Study (RAPS) show that plume entrainment into the rising mixing layer is completed by 1000 Central Daylight Time (CDT). Due to daytime vertical mixing and nocturnal decoupling, the dry removal rate for the elevated plume is highest near noon. In a daily cycle, the plume sequentially passes through a reservoir regime, dissociated from delivery to the ground and then enters the mixing-removal regime.A two-box model representing the two regimes, with diurnally periodic rate constants for transformation and removal, is employed to estimate plume sulfur budgets. Ignoring wet removal, 30–45% of the SO₂ is estimated to be converted to S_p, half within the first day. Particulate sulfur is formed unevenly: the afternoon plume contributes more than its share because it rises so high that it has more time to react before removal begins. In short: transformation and removal occur mainly during the daytime, while transport is fastest at night. After a hard day of convection, reaction and deposition, the lower atmosphere relaxes at dusk while the midwestern plume takes off overnight on a jetstream and begins the next day's work 300–400 km from the stack.     

Concentration fluctuations in a smoke plume

Previous research results are reviewed and used to derive a new set of analytical formulas for predicting concentration fluctuations in smoke plumes. The meandering plume approach and the internal plume approach are compared. Some simple models are tested with field and laboratory data sets, showing that several aspects of the data (e.g. the concentration fluctuations on the plume axis) are reasonably wellsimulated. However, there is much room for improvement, since the models have some fundamental disagreements and much more testing with data should take place. In particular, a good knowledge of the Lagrangian time scale is essential for predicting concentration fluctuations.