Showing papers in "Journal of the Air Pollution Control Association in 1977"
TL;DR: In this article, the aerodynamic resistance to vertical transfer in the surface boundary layer can be formulated in terms of the friction velocity, height of observation, vertical heat flux, and surface roughness.
Abstract: The deposition of sulfur dioxide on growing vegetation is affected by diverse environmental factors, many of which undergo large diurnal and spatial variations. The aerodynamic resistance to vertical transfer in the surface boundary layer can be formulated in terms of the friction velocity, height of observation, vertical heat flux, and surface roughness. Also important are the resistance in the air layer closest to the surface elements and, in dry vegetation, the average stomatal resistance of the plants. The latter variable is among the most difficult to estimate, but over many agricultural field crops like those in the midwestern U.S., a typical minimum value of average stomatal resistance to SO2 transfer is about 0.7 s cm-1, as is indicated by various experimental data. The deposition velocity can be estimated as the inverse of the sum of the resistances of the layers, necessarily down to where the concentrations are zero; in the surface boundary layer, any of the various resistances might be dominant...
566 citations
TL;DR: In this article, the authors examined published data for many locations and showed that the %th wind profile power law is often unrepresentative of actual conditions because the degree of variation of wind speed with height depends greatly on atmospheric stability.
Abstract: Recent environmental regulations have increased the need for construction of meteorological towers at power generation facilities. Due to practical and economic considerations, tower heights are usually lower than effluent release heights. At heights where wind speed data are not available, the wind speed is usually estimated from the measured wind speed using the %th wind profile power law and assuming neutral stability conditions. This study examines published data for many locations and shows that the %th wind profile power law is often unrepresentative of actual conditions because the degree of variation of wind speed with height depends greatly on atmospheric stability. The frequency of neutral stability conditions also varies appreciably by site. These two considerations are especially important in dispersion models which extrapolate wind speed at stack height from low level wind speed data.
136 citations
TL;DR: It is concluded, based upon the results of this study, that any environmental control strategy should address both the air and the soil.
Abstract: This paper is directed to those persons concerned with the relationship between blood lead levels and environmental exposures to lead. Information presented in this paper represents one of the largest collections of epidemiologica! data relating blood lead levels to environmental exposures. The observed annual average ambient air lead concentration ranged from approximately 0.5 ng Pb/m3 to 23 ng Pb/m3, while lead in soil ranged from 50-24,600 ppm. Blood lead levels of children (ages 1-9 years) are related to a host of environmental variables via regression techniques. Blood lead levels were found to be most influenced by five variables. These variables are: ambient air lead, soil lead, age of the child, dustiness of the home, and occupational status of the parents. It is concluded, based upon the results of this study, that any environmental control strategy should address both the air and the soil. Soil levels in excess of 1000 ppm lead as well as air lead levels greater than 2 jug Pb/m3, 30 day average,...
123 citations
TL;DR: In this article, tracer gas was measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 68 ft/sec.
Abstract: Steady state mean concentrations of tracer gas were measured in a 400:1 scale model of an idealized city with variable geometry placed within a wind tunnel at various orientations to the mean flow for a free stream velocity of 68 ft/sec The tracer gas was released from two parallel line sources to simulate lanes of traffic in an effort to quantify the persistence of pollution as well as the mean values realized at street levels An aerodynamically rough turbulent boundary layer of neutral thermal stratification was employed to simulate the atmosphere Values of concentration measured in the model city were converted to prototype concentrations in ppm and compared to National Ambient Air Quality Standards It was shown that single isolated structures may cause favorable mixing of pollution downwind but very high concentrations exist in the immediate leeward vicinity of the building Two favorable geometries for city blocks tested were found to reduce pedestrian exposure to pollution both near heavy traff
95 citations
TL;DR: In this article, the authors describe an approach that treats this process from a chemical kinetics viewpoint; it has led to the design of a chemical reactor system suitable for plant growth and exposure, while meeting criteria necessary to apply the concept of a continuous stirred tank reactor.
Abstract: Available chamber designs and experimental techniques have not permitted a critical appraisal of uptake of gaseous pollutants by plants. This work describes an approach that treats this process from a chemical kinetics viewpoint; it has led to the design of a chemical reactor system suitable for plant growth and exposure, while meeting criteria necessary to apply the concept of a continuous stirred tank reactor. Use of the system to study nitrogen dioxide uptake by corn [Zea mays (L.) 'Pioneer Brand 3369A'] and soybean [Glycine max (L.) Merr. 'Davis'] under several exposure conditions is presented. The system provided precise data that were readily amenable to mathematical modeling. The concept of a second-order rate constant for uptake is demonstrated, which is shown to be independent of nitrogen dioxide concentration and leaf surface area, but directly dependent upon inverse total diffusion resistance.
80 citations
TL;DR: It has long been recognized that information on particle size distributions in atmospheric aerosals is necessary for meaningful evaluations of potential health hazards and is also important in establishing particulate sources, transport, transformations, and sinks, especially in combination with elemental and chemical data.
Abstract: It has long been recognized that information on particle size distributions in atmospheric aerosals is necessary for meaningful evaluations of potential health hazards. Such information is also important in establishing particulate sources, transport, transformations, and sinks, especially in combination with elemental and chemical data. While instruments exist to collect size segregated samples of particulates, they are too complex and expensive to encourage use of multiple units in field situations.
74 citations
TL;DR: In this paper, a mass transfer approach is used in developing a practical mathematical model of gaseous pollutant uptake by leaves in which a series of resistances is summed across a concentration difference.
Abstract: A mass transfer approach is used in developing a practical mathematical model of gaseous pollutant uptake by leaves in which a series of resistances is summed across a concentration difference. The body of information presented in this paper is directed to plant pathologists or physiologists in the field of vegetal-pollutant effects and to people interested in the natural removal of air pollutants by vegetation. Correlations are given to calculate the aerodynamic and the stomatal resistances to uptake, while both a qualitative investigation and quantitative estimates are made of the mesophyllic resistance. The factors which control the aerodynamic resistance, ra, are leaf size and wind speed, while the leaf physiology is the determinant of the stomatal resistance, rs . It is noted that the chemical reaction rate and pollutant diffusivity in the mesophyll control the mesophyllic resistance, rm, though the overall gas phase mesophyllic resistance, Hrm, is strongly a function of pollutant solubility in water...
73 citations
TL;DR: In this paper, a plot of measured values of the photolysis rate J1 vs Eppley uv photometer readings produces a curved rather than the straight line correlation previously reported.
Abstract: Improvements made on the direct NO2 photolysis actinometer developed by J. O. Jackson have produced more precise data. A plot of measured values of the photolysis rate J1 vs Eppley uv photometer readings produces a curved rather than the straight line correlation previously reported. This curvature arises from the Eppley and NO2 absorption spectrum overlap, backround surface albedoes, the Ep-pley's cosine response and inherent errors in the chemical equation used. New J1 measurement vs Eppley data is shown, and a procedure for calculating instantaneous J-i values from an Eppley output is suggested.
71 citations
TL;DR: The main elements and features of precipitator equipment used for the collection of fly ash are presented in this paper, and the major types of problems encountered in the application of precipitor to the collecting of fly-ash are enumerated and approaches for solving and avoiding these problems indicated.
Abstract: The main elements and features of precipitator equipment used for the collection of fly ash are presented. The major types of problems encountered in the application of precipitators to the collection of fly ash are enumerated and approaches for solving and avoiding these problems indicated. A summary of the fundamental problems, mechanical problems and operational problems commonly met with in practice is presented. The vital importance of relying on scientific and systematic methods for diagnosing and correcting the varied problems which may arise is emphasized. Several case histories of fly ash precipitators are given to illustrate the principles, methods, and practices covered in the preceding sections of the paper. Performance specifications, design and actual performance data are presented for medium sulfur eastern coal, high sulfur midwestern coal and low sulfur Rocky Mountain coal. In each case the information and data used are based on first-hand knowledge and close association of the author with the installation. Previous installments of the paper appeared in the January, February and March issue of JAPCA.
61 citations
TL;DR: A massive experiment was conducted at the General Motors Proving Ground to measure the dispersion of sulfates generated by catalysts and air pumps in a 10 km test track with a traffic density of 5462 cars/hour as discussed by the authors.
Abstract: A massive experiment was conducted at the General Motors Proving Ground to measure the dispersion of sulfates generated by catalyst equipped vehicles. 352 cars equipped with catalysts and air pumps were driven on a 10 kilometer test track to provide a simulated freeway situation with a traffic density of 5462 cars/hour. Experiments were conducted on 17 days in October 1975, providing sixty-six 30 min data sets. On most days, the experiment was carried out early in the morning in order to run under the most adverse meteorological conditions available. Samples of airborne sulfate and a gas tracer, sulfur hexafluoride, as well as extensive meteorological data were collected simultaneously at 20 sampling points under a wide variety of meteorological conditions. The maximum measured increase in sulfate from each 30 min data set was generally found next to the roadway at the lowest level and varied from 3 to 15 jug/m3. This increase in sulfate over background fell off rapidly with height and distance. Sulfate i...
52 citations
TL;DR: In this article, General Motors sponsored a study of sulfate exposures utilizing a fleet of catalyst equipped motor vehicles in controlled, simulated, highway driving conditions, and the results showed that sulfuric acid aerosol, in the Aitken nuclei mode, geometric mean diameter (GMD) of about 0.02 µm, is emitted in the exhaust of catalyst-equipped vehicles.
Abstract: In October 1975, General Motors sponsored a study of sulfate exposures utilizing a fleet of catalyst equipped motor vehicles in controlled, simulated, highway driving conditions. This paper reports some EPA sponsored measurements. Sulfuric acid aerosol, in the Aitken nuclei mode, geometric mean diameter (GMD) of about 0.02 µm, is emitted in the exhaust of catalyst equipped vehicles. Measurement of sulfuric acid 20 m downwind of the roadway indicated a lack of complete neutralization by ammonia. When the wind was perpendicular to the roadway there was little coagulation of sulfuric acid into the accumulation mode, GMD of about 0.24 µm From measurement of the mass flow rate of aerosol sulfur from the simulated freeway, the aerosol sulfur emission rate per car was determined to be 3.5 ± 0.8 µg/m (5.6 ±1.3 mg/mile) corresponding to a 12 ± 3% conversion of fuel sulfur into emitted aerosol sulfur.
TL;DR: In this paper, the trace constituents were identified using retention data on eight GC columns, their electron attachment properties, and their EC thermal response, and it was possible to determine their origin (natural or anthropogenic).
Abstract: Based on two comprehensive field studies conducted in California, background concentration (parts per trillion) of N/sub 2/O (296.0 x 10/sup 3/), SF/sub 6/ (0.16), CCl/sub 2/F/sub 2/ (180.8), CCl/sub 3/F (103.8), CCl/sub 2/FCClF/sub 2/ (16.3), CCl/sub 4/ (114.2), CH/sub 3/Cl (952.9), CHCl/sub 3/ (23.4), CH/sub 3/I (2.4), CH/sub 3/CCl/sub 3/ (84.0), CCl/sub 2/CCl/sub 2/ (43.1), CHClCCl/sub 2/ (14.5) and CH/sub 3/Br (-) have been reported. These trace constituents were identified using retention data on eight GC columns, their electron attachment properties, and their EC thermal response. All but CHClCCl/sub 2/ and CH/sub 3/BR were measurable 100% of the time at both sites. Cryogenic procedures for SF/sub 6/ ambient measurements were developed and successfully used. By an analysis of worldwide emissions of these trace constituents, their ambient levels, and their atmospheric lifetimes, it was possible to determine their origin (natural or anthropogenic). Our results indicate that 27% of organic chlorine contribution to the troposphere comes from fluorocarbons as opposed to a 73% contribution from the chlorocarbons. Further, the anthropogenic organic content in the troposphere was found to be about twice the natural content. Very high CHCl/sub 3/ concentrations in onshore ocean waters were measured. Ambient data supporting the anthropogenic origin ofmore » CCl/sub 4/ have been presented.« less
TL;DR: In this paper, a standardized system of site selection is proposed to improve the comparability and meaningfulness of data obtained from different air monitoring stations throughout the United States, by considering the location of a monitoring station relative to nearby sources, particularly for carbon monoxide and other vehicular pollutants.
Abstract: A critical problem arises if one attempts to compare data from air monitoring stations in different cities, because there are so many differences in monitoring site locations. Some air monitoring stations are on the 6 th and 8 th floors of tall buildings in downtown areas; some are at ground level beside streets with heavy traffic; some are in residential areas with little traffic or industry; and some are in suburban or nonurban areas. Unfortunately, there is ample evidence that the location of a monitoring station relative to nearby sources (such as highways) affects the values observed at the station, particularly for carbon monoxide and other vehicular pollutants. Thus, a standardized system of site selection, such as the one proposed here, appears essential to improve the comparability and meaningfulness of data obtained from different air monitoring stations throughout the Nation.
TL;DR: In this paper, the authors developed a theoretical expression for the cohesive force in an idealized dust layer which takes into account the increase in effective contact area between adjacent particles due to elastic deformation and the limiting of the electric field in the air gap to a maximum allowable value.
Abstract: One of the important cohesive forces acting on the precipitated layer in an electrostatic precipitator Is that due to the effect of the electric field established in the air gaps between adjacent particles by the corona current as it flows through the layer. A theoretical expression for this force is developed for an idealized dust layer which takes into account the increase in effective contact area between adjacent particles due to elastic deformation and the limiting of the electric field in the airgap to a maximum allowable value. It is shown that the cohesive force is approximately proportional to the electric field established across the layer. This relationship is in general agreement with measurements made in the laboratory using industrially produced dust samples.
TL;DR: In this article, ozone chlorotic mottle on ponderosa pine appeared from about 1000 m altitude, increased in severity as elevation increased and then diminished in severity above 2600 m. An apparent east to west gradient of disease was discovered; severity lessened as distance from the Central Valley increased.
Abstract: Numerous oxidant-injured ponderosa pine and other tree species have been detected in the lower elevation forests of the southern Sierra Nevada mountain range of California in the Sequoia National Forest, Sequoia-Kings Canyon National Parks, and on state and private lands. Affected pines were observed in a broad band following the many ridges that rise above the Central Valley floor to the 1900--2600 m elevation. Slight symptoms of ozone chlorotic mottle on ponderosa pine appeared from about 1000 m altitude, increased in severity as elevation increased and then diminished in severity above 2600 m. An apparent east to west gradient of disease was discovered; severity lessened as distance from the Central Valley increased. Atmospheric monitoring in three forested sites suggests that ozone occurs in doses sufficient to elicit symptoms of this widespread disease.
TL;DR: In this paper, the overall particle collection efficiencies of spray scrubbers using monodisperse droplets of 100,500, and 1000 microns diameter were calculated for the cases of evaporating and condensing droplets.
Abstract: The overall particle collection efficiencies of spray scrubbers using monodisperse droplets of 100,500, and 1000 microns diameter were calculated for the cases of evaporating and condensing droplets. The properties of the gas at the inlet to the spray scrubber were maintained constant at 150°F, 100% relative humidity, and 1 atmosphere pressure. At the liquid entrance to the spray scrubber, the water droplet temperature was 50° F for the condensing case and 180° F for the evaporating case. The liquid to gas flow rate ratio for all the calculations was held constant at 4 gal/1000 acf. The gas velocity in the co-current spray tower was 1 ft/sec in the downwind direction. The calculation results show that for the particles in the 0.01 to 10 Mm diameter range, the overall spray scrubber particle collection efficiency is greater with the cooler 50°F water (condensing case) than with the warmer 180°F water (evaporating case). The effect of diffusiophoresis and thermophoresis is noticeable for all the water dropl...
TL;DR: In this article, Pinto beans and Bel W3 tobacco were grown and exposed to 40 pphm ozone for 1 hour under a range of light intensities, temperatures, and relative humidities.
Abstract: Pinto bean (Phaseolus vulgaris, L.) and Bel W3 tobacco (Nicotiana tabacum, L.) were grown and exposed to 40 pphm ozone for 1 hr under a range of light intensities, temperatures, and relative humidities. Foliar injury to the more sensitive plant leaves was determined on the third day after exposure. Each atmospheric factor was independently assessed. Two significant three-way interactions were found: exposure light intensity by growth light intensity by species, and growth temperature by exposure temperature by species. Three significant two-way interactions were found for humidity: growth humidity by exposure humidity, growth humidity by species, and exposure humidity by species. The sensitivity of each species to ozone changed with changes in each environmental condition.
TL;DR: In this article, a two-parameter averaging-time model was proposed for urban air pollution data, where pollutant concentrations are lognormally distributed and lognormal distributed.
Abstract: Urban air pollutant concentration data often tend to fit a two-parameter averaging-time model having three characteristics: (1) pollutant concentrations are (two-parameter) lognormally distributed ...
TL;DR: For the upwind dispersion, the model is inapplicable for stable conditions and variable winds at different heights and plume-rise due to the heated exhaust completely invalidate the model as discussed by the authors.
Abstract: A major objective of the General Motors Sulfate Dispersion Experiment was to investigate the validity of the Environmental Protection Agency's HIWAY dispersion model. This model was the basis for the high roadside predictions made by EPA in 1975. Comparisons of measurements with predictions show that at the pedestrian level downwind from the road, the model works fairly well under unstable conditions, but overpredicts for stable conditions. The overpredictions get worse as the wind speed decreases, as the wind direction becomes parallel to the road, and as the distance from the road increases. For the upwind dispersion, however, the model Is inapplicable. Under extremely stable or worst meteorological conditions, variable winds at different heights and plume-rise due to the heated exhaust completely invalidate the model. The overpredictions at the bottom level downwind can be very substantial. When the wind is parallel to the road, overpredictions occur at all sampling positions. New dispersion parameters...
TL;DR: Gelman's Spectro Grade and AE filters yielded the highest values and Gelman Type A the lowest as discussed by the authors, assuming that catalytic conversion produces erroneously high data, one might be inclined to conclude that Type A was superior to the others; however, additional studies on collection efficiencies and interaction effects with filter constituents would be required before such a conclusion would be warranted.
Abstract: Atmospheric particulates, collected on four different types of filters (Gelman A, AE, Spectro Grade, and a special batch of Type A supplied by the EPA) in a side-by-side comparison showed differences in total suspended particulates (TSP) and lead loading as high as 20 and 17 percent, respectively (using Gelman A as a reference). The differences in sulfate and nitrate were even greater, running as high as 49 and 219 percent, respectively. Catalytic conversion of SO/sub 2/ and NO/sub 2/ to particulate sulfate and nitrate on contact with the filter surface is believed responsible for the anomalously high values observed. For all of these parameters (i.e., TSP, lead, sulfate, and nitrate) Gelman's Spectro Grade and AE filters yielded the highest values and Gelman Type A the lowest. Based on these results and assuming that catalytic conversion produces erroneously high data, one might be inclined to conclude that Type A was superior to the others; however, additional studies on collection efficiencies and interaction effects with filter constituents would be required before such a conclusion would be warranted. The results do indicate that the type of filter medium used in hi-vol sampling has a pronounced effect on the results. It therefore becomes imperativemore » that all agencies involved in air monitoring surveillance standardize on a single filter medium as soon as possible. This priority becomes even more urgent in view of the 25 ..mu..g/m/sup 3/ sulfate standard recently imposed by the California Air Resources Board. The long-range goal should be the development of a filter for which the catalytic conversions are either eliminated or at least held to a minimum (i.e., 5 percent or less).« less
TL;DR: In this paper, biochemical and physiological experiments were conducted on pea plants (Pisum sativum) continuously exposed in growth chambers to SO2 gas for 18 days, and S02 gas concentrations were 0.1, 0.15, and 0.2.
Abstract: Biochemical and physiological experiments were conducted on pea plants (Pisum sativum) continuously exposed in growth chambers to SO2 gas for 18 days. S02 gas concentrations were 0.1, 0.15, and 0.2...
TL;DR: The demolition, especially the “explosive demolition” of buildings which have been fireproofed and/or insulated with asbestos-containing materials may be the most significant future source of asbestos emissions unless adequate precautions are taken.
Abstract: The relationship between asbestos consumption and mesothelioma incidence in Connecticut has been investigated. Asbestos has many industrial applications; however, several of these result in the dissipation of this material (e.g., vehicle brake and clutch lining erosion). In Connecticut, asbestos manufacturing operations contribute approximately 10 tons of airborne asbestos fibers each year, while vehicle brake and clutch lining erosion add another 2 tons. The demolition, especially the “explosive demolition” of buildings which have been fireproofed and/or insulated with asbestos-containing materials may be the most significant future source of asbestos emissions unless adequate precautions are taken. Occupational asbestos fiber exposure has been known to cause asbestosis, lung cancer, and cancer of the lining of the stomach and lung (mesothelioma) for some time. Recently, the previously rare mesothelial malignancy has been linked to nonoccupational asbestos fiber exposure as well. There were 133 Conneticu...
TL;DR: In this paper, a mathematical model based on experimental results was developed to describe dust transfer from bag to bag, redeposition on the pulsed bag itself, and migration to the dust hopper.
Abstract: Pulse-jet filter cleaning is ineffective to the extent that collected dust redeposits rather than falls to the hopper. Dust tracer techniques were used to measure the amount of redeposition in a pilot scale pulse-jet filter. A mathematical model based on experimental results was developed to describe dust transfer from bag to bag, redeposition on the pulsed bag itself, and migration to the dust hopper. Dust redeposition upon the pulsed bag increased markedly with increasing filtration velocity, whereas migration and redeposition on bags adjacent to the pulsed bag decreased. For high velocity pulse-jet filters to operate at lowest possible pressure drop, filter cake redeposition must be minimized.
TL;DR: In this paper, the sodium arsenite method for measurement of nitrogen dioxide in ambient air was evaluated and found to have a constant high collection efficiency (82%) for nitrogen dioxide, and is insensitive to normal variations in operating parameters.
Abstract: The sodium arsenite method for measurement of nitrogen dioxide in ambient air was evaluated. The method has a constant-high collection efficiency (82%) for nitrogen dioxide, and is insensitive to normal variations in operating parameters. Nitric oxide and carbon dioxide are positive and negative interferents, respectively. The combined average effect of these interferents, over ambient levels, is a positive bias of 9.9 µg/m3. This bias, although statistically significant, is minor ( 10 % ) in relation to the ambient air standard of 100 µg NO2/m3 and does not warrant modification of the method to remove the interference.
TL;DR: In this paper, the results of a series of tests conducted upwind and downwind of several major metropolitan and industrial complexes, which include Phila-delphia-Camden-Wilmington and New York City-Northeastern New Jersey-Southeastern Connecticut, were reported.
Abstract: Aerial ozone measurements were obtained during the summer of 1975 in the Northeastern United States. This paper reports on the results of a series of tests conducted upwind and downwind of several major metropolitan and industrial complexes, which include Phila-delphia-Camden-Wilmington and New York City-Northeastern New Jersey-Southeastern Connecticut. Flight patterns consisted of upwind and downwind tranverses perpendicular to the urban plume and vertical profiles. The results indicate significant O3 generation occurs in the urban plumes, but at no time was the difference between the upwind and downwind O3 concentrations greater than 0.08 ppm (maximum 0.078 ppm). However, in several cases when the upwind values were added to the O3 produced by the urban area, this was sufficient to result in violations of the NAAQS downwind. The paper also discusses the results of flights over refineries and petrochemical facilities which yielded a positive contribution to downwind O3 values.
TL;DR: In this paper, the photosynthetic activity of the blue-green algae studied was almost totally inhibited by 0.1 mM bisulfite and 1.0 mM nitrite.
Abstract: Microorganisms were exposed to bisulfite at concentrations of 0.1 and 1.0 mM and nitrite of a concentration of 1.0 mM. Results show that the photosynthetic activity of the blue-green algae studied was almost totally inhibited by 0.1 mM bisulfite. By contrast, the other algae generally showed little or no inhibition by 0.1 mM bisulfite; this group of resistant species included 14 green algae, 2 yellow algae, a red algae, and EUGLENA GRACILIS. Similarly, the 8 genera of blue-green algae were consistently sensitive to 1 mM nitrite. On the other hand, not one of the 10 green and yellow algal genera tested was appreciably inhibited by nitrite at this concentration. The potential sensitivity of blue-green algae to atmospheric sulfur dioxide is particularly interesting because the blue-green algae are the dominant nitrogen-fixing organisms in some ecosystems.
TL;DR: One of the most annoying aspects of photochemical air pollution, particularly in the Southern California Air Basin, has been eye irritation, which was a strong motivation for the public to demand that effective control actions be taken.
Abstract: One of the most annoying aspects of photochemical air pollution, particularly in the Southern California Air Basin, has been eye irritation. The most aggravating combination of driving in heavy traffic in Los Angeles, suffering from tearing and burning of the eyes together with very limited visibility, was a strong motivation for the public to demand that effective control actions be taken.