Particulate Matter from Stone Crushing Industry: Size Distribution and Health Effects

A cluster of 50 stone crushing units located at Pammal, in suburban Chennai, the capital of Tamil Nadu State, India, is a source of high levels of dust generation in the vicinity of the crushers and in the communities surrounding them. Ambient air quality network consisting of 26 sampling locations were operated to continuously monitor the total and respirable particulate matter concentrations (TSP and PM10). The daily average ambient concentrations of TSP and PM10 varied from 342 to 2,470 and 90 to 1,200?μg/m3, respectively, near the source, while the average concentrations varied from 86 to 257 and 39 to 138?μg/m3 in ambient air. The average PM2.5 concentration varied from 41 to 388?μg/m3 at the source, whereas the concentration varied from 17 to 48?μg/m3 in ambient air. Personal samplers were also employed to quantify the TSP and RPM in the work environment and they varied from 22.5 to 80.5 and 13.5 to 53.7?mg/m3, respectively. Both ambient concentrations and occupational exposure levels exceeded the Indian National Standards at most of the locations. Pulmonary function tests performed on workers showed that the average values of pulmonary function in these workers are significantly lower than the average values reported for normal South Indian healthy males.     

Sorption of Statin Pharmaceuticals to Wastewater-Treatment Biosolids, Terrestrial Soils, and Freshwater Sediment

The sorption kinetics and equilibrium endpoints of two widely prescribed anionic lipid-regulating pharmaceuticals—atorvastatin and simvastatin acid—were evaluated for wastewater-treatment plant primary clarifier biosolids, a peat soil, a sandy soil, and a stream sediment. All equilibrium isotherms were linear over an aqueous concentration range of 0.01?μg/L to greater than 100?μg/L. Log?Koc values for statin sorption to biosolids were 2.91 and 2.96 for atorvastatin and simvastatin acids, respectively. Comparative isotherm experiments with the peat soil, sandy soil, and stream sediment found log?Koc values for atorvastatin of 2.96, 2.70, and 3.20, respectively, and values of 2.89, 2.81, and 3.33 for simvastatin acid, respectively. Sorption was noncompetitive between the two statin drugs. Temperature changes did not affect sorption of either statin over the range of 5–32°C, indicating that heats of sorption were near zero. Taken together, these observations suggest that despite its anionic structure, statin sorption occurs via partition (solubilization) of the hydrophobic part of the molecule into the sorbent organic matter. Results from kinetic experiments show that statin sorption to biosolids reaches equilibrium much more rapidly compared to the soils and sediment, as the mass-transfer-rate coefficient, α, for the two-site equilibrium/kinetic model is approximately one-order-of magnitude higher for the biosolids. Presentation of these sorption data provides a requisite first step for future studies of statin fate and transport in wastewater-treatment plants and the environment.     

Episode Simulation of Asian Dust Storms with an Air Quality Modeling System

T A dust deflation module was developed and coupled with the air quality modeling system RAMS-CMAQ to simultaneously treat all the major tropospheric aerosols (i.e., organic and black carbons, sulfate, nitrate, ammonia, soil dust, and sea salt). Then the coupled system was applied to East Asia to simulate Asian dust aerosol generation, transport and dry/wet removal processes during 14-25 March 2002 when two strong dust storms occurred consecutively. To evaluate model performance and to analyze the observed features of dust aerosols over the East Asian region, model results were compared to concentrations of suspended particulate matter of 10 μm or less (PM10; 1-h intervals) at four remote Japanese stations and daily air pollution index (API) values for PMio at four large Chinese cities. The modeled values were generally in good agreement with observed data, and the model reasonably reproduced two dust storm outbreaks and generally predicted the dust onset and cessation times at each observation site. In addition, hourly averaged values of aerosol optical thickness (AOT) were calculated and compared with observations at four Aerosol Robotic Network (AERONET) stations to assess the model's capability of estimating dust aerosol column burden. Analysis shows that modeled and observed AOT values were generally comparable and that the contribution of dust aerosols to AOT was significant only with regard to their source regions and their transport paths.     

A Model to Estimate the Delivered Doses of Substances in Liquid and Gaseous Phases

A conceptual model is presented for assessing the dose of a chemical substance delivered to individual lung cells when exposure can occur through inhalation of the substance as either a gas or an aerosol of droplets. Assuming a threshold value for the concentration of a toxic species in a single cell, the model shows that the physical state of the substance may affect its biologic activity. Exposure to aerosol droplets of an irritating or reactive substance will deliver much higher surface concentrations to single cells than will a similar exposure to a gas. Under certain conditions, the surface concentration can be between 100 and 10¹0; times higher when the exposure involves an aerosol. Indirect support for the model is found in the observations that threshold limit values for aerosols are generally lower than those for gases.     

Distribution of Metals for Particulate Matter Transported in Source Area Rainfall-Runoff

In urban drainage, metals partition between dissolved (fd) and particulate (fp) phases. Metals also distribute across particulate matter (PM) gradations. In this study, granulometric metal distributions were examined for similar urban paved source areas in Baton Rouge, La.; Cincinnati; New Orleans; Little Rock, Ark.; and N. Little Rock, Ark. Metal distributions were examined for PM fractions from <25?μm to >4,750?μm, as suspended (< ～ 25?μm), settleable ( ～ 25–75?μm), and sediment (>75?μm bed load) fractions. For all areas, analysis of PM indicated that metal mass and concentration (mole/m2) were distributed across the gradation. A cumulative gamma distribution constitutive model related metal mass and PM size. The study focused on Baton Rouge, La. where event-based and composited PM metal distributions were statistically similar. For influent and settled runoff, fp dominated Cr, Cu, Zn, As, Cd, and Pb partitioning. Influent Cu, Zn, Cd, and Pb exceeded discharge criteria for receiving water beneficial uses on a total metal basis. A constitutive model for Pb and Zn mass distributions at Baton Rouge, La. was combined with Newtonian settling and ideal overflow rate to examine two limiting cases of storm events loading a screened hydrodynamic separator. For low and high flow events, modeling reproduced metal mass of eluted PM (2 to ～ 250?μm) from an HS within 4% of measurement, but when influent Pb and Zn exceeded discharge criteria so did HS effluent. As a separate unit operation, 1 h of quiescent settling did reduce Pb, but not Cu, Zn, and Cd to discharge criteria levels.     

Value and limits of surgery in stage IIIB non-small-cell bronchial cancers

Storage of radon-producing material in two silos and two waste pits is one of the major environmental and occupational issues at a former uranium production facility, now a Superfund site. In addition, up to 100 metric tons of thorium is stored on the northeast side of the site. Concentrations of radium up to 17,600 Bq g(-1) (477,000 pCi g(-1)) or higher for silos and up to 45 Bq g(-1) (1,200 pCi g(-1)) for waste pits have been reported. This study was conducted to identify factors and climatic conditions that contribute to higher radon levels and to assess workers' exposure at the site. Data covering a 12-mo period were compiled from monitoring hourly real-time radon levels at indoor (within 3 buildings) and outdoor (at 14 on-site and 2 off-site monitoring stations) locations and from hourly site-specific meteorological information. The ranges of radon levels were as follows: 1.8-3,655 Bq m(-3) (0.05-98.8 pCi L(-1)) outdoor on-site, 3.7-329 Bq m(-3) (0.1-8.9 pCi L(-1)) outdoor off-site, and 1.8-111 Bq m(-3) (0.05-3.0 pCi L(-1)) indoor on-site. Only radon levels in the vicinity of the storage silos were significantly higher than levels off-site. Radon concentrations showed diurnal variations, with maximum levels occurring in the early morning and minimum levels in the afternoon. Seasonal variation was also observed, with radon levels higher during the summer through early fall and lower during the late winter through spring. Wind speed, relative humidity, and wind direction appeared to be the most significant predictors of radon concentration. The estimated radon dose to workers, calculated by using exposure models and annual average levels of radon in the work area, was below recommended exposure limits. These results suggest that the emission control methods at this site have been effective in maintaining environmental radon contamination and workers' exposure at acceptable levels.     

Study on Pb and PAHs Emission Levels of Heavy Metals- and PAHs-Contaminated Soil during Thermal Treatment Process

The objective of this study was to use thermal treatment to treat soil contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). The emissions of lead (Pb) and PAHs during the thermal treatment process were evaluated. The parameters included pretreatment, temperature, and speed of the rotary kiln. Cadmium (Cd) had a higher mobility in thermally treated contaminated soil slag than other heavy metals because the primary fraction of Cd was the exchangeable fraction (90%). Of the temperatures tested in this study, the highest emission concentration of Pb occurred at 700°C. The Pb emission concentrations in the gas phase and solid phase were 44?μg/N?m3 and 138.35?μg/N?m3, respectively. In PAHs emissions, naphthalene, acenaphthene (Acp), and fluorene were the main species in the gas phase, at different operating temperatures. The concentrations of these species ranged from 615.5 to 2,002.3?μg/N?m3. Acp and chrysene were the main species in the solid phase at different temperatures, and the concentrations of these species ranged from 25.5 to 113?μg/N?m3.     

Modeling Arsenite Adsorption on Rusting Metallic Iron

Experimental data on As(III) adsorption by rusted zero valent iron (ZVI) could be modeled using a simple Langmuir isotherm model. However, the adsorption equilibrium was observed to shift with time, as continued rusting produced additional sites on the rusted ZVI surface for potential arsenic adsorption. A modified Langmuir isotherm model was formulated taking into consideration the temporal variation in the site concentration for potential arsenic adsorption on the rusted ZVI surface. This model simulated the long-term experimental data on As(III) adsorption quite well. The model was further refined by apportioning the arsenic adsorbed on the rusted ZVI surface into labile and irreversibly adsorbed fractions. Finally, the developed model was used to simulate the performance of an adsorption column. The simulation results indicate that an adsorption column of length 0.4 m and diameter 0.056 m, i.e., containing 0.001?m3 of rusted ZVI weighing 4.76 kg, and operated at an empty bed contact time of 12 min, can treat 2,375–2,525 L of water containing 100?μg?L?1 of As(III) such that the effluent As(III) concentration from the column is less than 10?μg?L?1.     

Enteric Virus Indicators: Reovirus Versus Poliovirus

The resistance of reovirus to inactivation by mesophillic and thermophillic temperatures was investigated and compared to existing inactivation patterns for poliovirus, the most commonly used enteric virus indicator. The resistance of reovirus to alkaline condition resulting from the addition of lime (CaO) to biosolids was also examined. Phase one involved the incubation of reovirus in a buffered solution for a 28-day period at different temperatures ranging from 4?to?50°C. This phase also involved reovirus incubation at thermophillic temperatures ranging from 50?to?55°C for a 30-min period. The second phase looked at reovirus survival in biosolids mixed with lime doses ranging from 0?to?100?g lime per kg dry biosolids over a 23-day period. Reovirus was more resistant to inactivation caused by long-term storage under mesophillic temperature conditions than poliovirus. Reovirus also was more resistant to inactivation caused by short-term storage under thermophillic temperature conditions than poliovirus. Reovirus has shown to be stable in biosolids under naturally occurring environmental conditions for up to 1?year, while doses of 80?g lime per kg dry biosolids and greater were able to meet class A levels for enteric viruses after 1?day of storage.     

Autistic behavior in young boys with fragile X syndrome

BACKGROUND: Various studies have demonstrated the benefits of continuous nebulization therapy for delivering aerosols of the beta2 agonists such as terbutaline sulfate or albuterol sulfate to patients with severe asthma and/or impending respiratory failure. OBJECTIVE: The purpose of this investigation was to explicate the operational factors associated with the use of nebulizers for extended aerosol respiratory therapy including those factors that affect the prescribed aerosol dosages and the relationship to actual delivery of prescribed drugs to the respiratory airways of the lungs of a patient under treatment conditions. METHODS: Operational characteristics and methods have been investigated for use of long-running nebulizers for continuous nebulization therapy. Factors considered were particle size distribution, setup conditions, aerosolization concentrations and rates, delivery fraction of aerosol reaching patient, and changes in medication concentration during extended operation. With a large volume nebulizer, aerosols can be delivered to the patient without dilution via a standard open mask for up to eight hours without refill. The pneumatic HEART nebulizer with 240 mL reservoir was evaluated. RESULTS: The nebulizer was operated from a single compressed air or oxygen source and found to provide from 10 to 15 L/min of aerosol with 38 to 50 microL of aerosolized medicine per liter of air (or oxygen) and utilize from 30 to 56 mL/hour of medicinal liquid. The mass median aerodynamic diameter of the aerosol droplets was found to be about 2.0 microm (sigma(g) = 2.7). Delivery efficiency to the patient mask was about 90%. The aerosolized medicine delivered to the patient can be increased by adjusting the flow rate of the gas source or changing the solution concentration of medicine. Typically, several milligrams of drug can be delivered to the patient as inhaled aerosol per hour of treatment of which about one-quarter can be expected to be deposited in the lungs. During eight hours of operation the concentration of medicinal solution increased by about a factor of two because of water evaporation. CONCLUSIONS: Continuous nebulization therapy is an important means of treating patients with severe asthma. Dosage criteria can be established based on the operating characteristics of the nebulizer system, drug solution concentration, and patient respiration.     

Nitrate Removal with Sulfur-Limestone Autotrophic Denitrification Processes

Nitrate removal using sulfur and limestone autotrophic denitrification (SLAD) processes was evaluated with four laboratory-scale fixed-bed column reactors. The research objectives were (1) to determine the optimum design criteria of the fixed-bed SLAD columns; and (2) to evaluate the effects of biofouling on the SLAD column performance. A maximum denitrification rate of 384 g NO3?-N/(m3?day) was achieved at a loading rate between 600 and 700 g NO3?-N/(m3?day). The effluent nitrite concentration started to rise gradually once the loading rate was above 600 g NO3?-N/(m3?day). A loading rate between 175 and 225 g NO3?-N/(m3?day) achieved the maximum nitrate-N removal efficiency (～95%). Biofouling was evaluated based on tracer studies, the measured biofilm thickness, and modeling. The porosities of the columns fluctuated with time, and the elongation of the filter media was observed. Biofouling caused short-circuiting and decreased nitrate removal efficiency. A SLAD column will require backwashing after 6 months of operation when the influent is synthetic ground water but will foul and require backwashing within 1–2 months when the influent is real ground water.     

Hydrodynamic Separation of Particulate Matter Transported by Source Area Runoff

Hydrodynamic separation is a preliminary unit operation frequently utilized in wastewater and more recently in storm water for separation of coarse particulate matter (PM) and gross solids. In order to examine the behavior and separation mechanisms of a screened hydrodynamic separator (HS) not influenced by scour, this study examined the event-based performance of an empty-bed (clean sump and volute) HS for PM fractions transported in eight runoff events from a 1,088?m2 paved source area urban watershed. Influent particle-size distributions (PSDs) {d50?m from 270?to?2,202?μm} and HS particle separation efficiency (PSE) (from 38 to 70% of mass) exhibited variations influenced by hydrology and previous loadings. When examined as PM size fractions, results demonstrate separation of the sediment fraction (>75?μm) ranging from 76 to 94% while for settleable and suspended (1–25?μm) fractions, the PSE was variable and significantly lower; from 3 to 57% and 2 to 43%, respectively. Results demonstrate a correlation between higher influent PM concentration and coarser PSDs, illustrating why higher PM concentrations promote higher PSEs; and why HS performance must be specified at a PM concentration, PSD, and flow rate. Results demonstrate that HS behavior is influenced by influent PSDs coupled with flow rate. Hydrodynamic separation is effective for high-rate gross solids control. However, current HS designs require incorporation of hydrologic control, methods of frequent sludge zone management before scour, and stored runoff management to control interevent redox conditions.     

Attenuation of Roadway-Derived Heavy Metals by Wood Chips

Wood chips were evaluated for their ability to attenuate heavy metals in roadway runoff. Column experiments with controlled synthetic runoff composition and flow rate were used to assess effects of flow rate (intercepted sheetflow from a 3-m wide roadway section), runoff salt concentration, wood exposure to alternating wetting and drying cycles, wood aging, competition among dissolved heavy metals, and removal of particle-associated heavy metals. Overall, wood chips damped the “pulse” of copper in the synthetic runoff such that the effluent was characterized by lower concentrations (3–25% of input) over longer periods of time, but with little retention of the total copper mass. The most effective treatment was wood chips aged up to 9 months. Increased aging and chip water content reduced effluent concentrations, relative to no treatment. Flow rate had no effect on effluent concentrations. The presence of salt (>2?mS/cm) or dissolved lead (500?μg/L) in the runoff caused greater copper effluent concentrations than the no treatment case. Removal of suspended particles (and associated contaminants) was greater than 85% with an estimated capacity of 0.16?g/gwood. Field evaluation with concentrated flow to a gutter containing a wood chip treatment showed little effect on total or dissolved copper and zinc runoff concentrations and indicated that wood chips may be a source of contaminants in subsequent storm events. Applications of wood chips to treat roadway runoff would not provide a significant decrease in total maximum daily load contributions (e.g., kg/d); however, there may be some scenarios for which wood chip treatments to decrease peak storm water concentrations of dissolved heavy metals in sheetflow runoff is desirable.     

Utility of Suspended Solid Measurements for Storm-Water Runoff Treatment

In this paper alternative solutions are presented to solve problems associated with the measurement of total suspended solids (TSS) in storm-water runoff. Results revealed that the accuracy of TSS measurement is largely related to sample representativeness, particle size distribution (PSD), sampling pipette position, and sample mixing. In general, when the PSD in the runoff was mostly larger than 75?μm, the most accurate and reproducible results were obtained when samples were collected from a position of mid-depth and midway between the walls of the beaker and the vortex and mixed at speeds in the range of 600–700?rpm. For runoff samples with a PSD smaller than 75?μm, mixing at a higher rpm is not a significant factor. As long as the PSD in the TSS subsample is representative of the original sample, a strong correlation between TSS and suspended solid concentration can be achieved. The results showed that density was largely correlated with the organic content of the particles, and, in general, smaller particles tended to have a lower density. The density results revealed that assuming a single sand size density of 2.6?g/cm3 for storm-water runoff produced a large error in the computation of sediment load and particle settling velocity.     

Ventilatory responses in awake guinea pigs exposed to acid aerosols

This study reports experiments designed to evaluate the dose and temporal effects of an atmospheric pollutant, sulfuric acid (H2SO4) aerosol, on the dynamic components of the respiratory cycle. Ventilation was measured in a whole-body barometric plethysmograph in unanesthetized, unrestrained animals following a 4-h exposure to H2SO4 aerosol at 14.1, 20.1, or 43.3 mg/m3. Lung injury was assessed by histopathology and bronchoalveolar lavage (BAL). Aerosol exposure with H2SO4 caused marked alterations in both the magnitude and composition of the ventilatory response, which were both dose and time dependent. At the highest concentration tested, there was a significant increase in tidal volume (deltaVt) and a decrease in breathing frequency (f) immediately after exposure. Analysis of BAL fluid at this time showed increased inflammatory cells and protein in the acid exposed animals, and histology showed hyaline membranes and acute inflammatory cells in the proximal acinar region. By 24 h postexposure, f significantly increased whereas deltaVt decreased. This pattern of breathing was interspersed with short periods of apnea. The onset of rapid, shallow breathing was associated with histological evidence of diffuse pulmonary edema. By contrast, the immediate postexposure period at the lowest concentration of H2SO4 aerosol was characterized by a significant increase in f and little or no effect on deltaVt. These effects diminished with time, and at 24 h postexposure ventilatory parameters were indistinguishable from baseline values. An apparent crossover between the effects associated with the high and low exposure concentrations was seen at the intermediate exposure concentration; however, closer inspection of these findings on an animal-by-animal basis revealed two populations of animals with respiratory characteristics of either the high-exposure or low-exposure groups. The data suggest that the guinea pig exhibits complex interactions between dose and time to response that are consistent with the activation of neural reflexes. The indirect plethysmographic method provides a simple means to assess these responses in a model system that avoids the use of anesthetics, surgery, and restraint.     

Use of aerosols to estimate pulmonary air-space dimensions

Single-breath inhalations of monodisperse aerosols were performed with a group of normal subjects to determine aerosol recovery from the human lung after periods of breath holding. Aerosols of monodisperse nonhygroscopic droplets of bis(2-ethylhexyl) sebacate of between 0.5 and about 2.5 micron diam were used for the inhalation. The inhalation apparatus allows continuous monitoring of particle number concentration and flow rate close to the mouth. Experiments were designed to find the optimum experimental conditions for the principal concept of Palmes et al (In: Inhaled Particles and Vapours. London: Pergamon, 1976, vol. II. p. 339-347) to evaluate pulmonary air-space dimensions by means of aerosols. The experimental results obtained for various respiratory flow rates (125, 250, and 500 cm3 X s-1), settling velocities of the particles (10(-3) to 1.5 X 10(-2) cm X s-1) and volumes of inspired aerosols (500, 1,000, and 2,000 cm3) are compared with the results derived from a mathematical model for the particle deposition during respiratory pauses. Monodisperse aerosols with particles between 1 and about 1.5 micron diam. inspired for breath holding into the lung region of interest, may provide optimum conditions for the sizing of air spaces by means of aerosols.     

Effect of microgravity and hypergravity on deposition of 0.5- to 3-micron-diameter aerosol in the human lung

We measured intrapulmonary deposition of 0. 5-, 1-, 2-, and 3-micron-diameter particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (microG) and at approximately 1.6 G. Subjects breathed aerosols at a constant flow rate (0.4 l/s) and tidal volume (0.75 liter). At 1 G and approximately 1.6 G, deposition increased with increasing particle size. In microG, differences in deposition as a function of particle size were almost abolished. Deposition was a nearly linear function of the G level for 2- and 3-micron-diameter particles, whereas for 0.5- and 1.0-micron-diameter particles, deposition increased less between microG and 1 G than between 1 G and approximately 1.6 G. Comparison with numerical predictions showed good agreement for 1-, 2-, and 3-micron-diameter particles at 1 and approximately 1.6 G, whereas the model consistently underestimated deposition in microG. The higher deposition observed in microG compared with model predictions might be explained by a larger deposition by diffusion because of a higher alveolar concentration of aerosol in microG and to the nonreversibility of the flow, causing additional mixing of the aerosols.     

Airborne Particles in New Museum Facilities

Over the period July 1996–April 1998, airborne particle concentrations and chemical composition were measured both inside and outside the new J. Paul Getty Museum outside Los Angeles. The purpose of these experiments was to determine the relationship between the stages of construction and operation of the building and the soiling hazard to the collections. Particular attention was paid to tracking the concentrations of fine black soot particles and mineral dust particles. The time needed to “air out” the building following construction can be seen from the data collected, as well as the inherent particle removal efficiency of the filters within the building ventilation system, and the effect of entry of the general public into the building. During the period of observation when the building was under construction, weekday coarse dust particle concentrations on occasion reached very high levels (600–1,100?μg?m?3; 24 h average), falling to relatively low values averaging 26?μg?m?3 over weekend periods when construction activity subsided. In March, 1997, with construction largely completed and with the heating, ventilation, and air conditioning (HVAC) system in full operation, indoor coarse dust concentrations fell to 1.7% of those outdoors. Beginning at this time, indoor fine particle concentrations relative to those outdoors declined steadily over a period of about one to two months, reaching levels of 3.9% of those outdoors during the period June 3–December 6, 1997 when construction was completed but before entry of the general public into the building. Thus, the coarse and fine particle removal efficiencies of the building HVAC system absent major indoor sources are at least 98 and 96%, respectively. Following the opening of the museum to the public, indoor particle concentrations increased by approximately 1?μg?m?3 in each of the coarse dust and fine smoke-size particle size ranges indicating that there is a small but measurable effect due to increased air infiltration as doors are opened and closed more frequently and due to particles shed by the visitors. Indoor particle concentrations inside the new Getty Museum in the presence of the general public are only 3.2?μg?m?3 of coarse dust and 1.8?μg?m?3 of fine particles on average over the period January–April, 1998.     

Estimating Solar and Nonsolar Inactivation Rates of Airborne Bacteria

Land application of biosolids is a wide spread practice in the United States, Canada, and Western Europe. Given the potential for biosolid aerosolization during land application, both solar and nonsolar induced inactivation rate information is needed to more accurately predict the fate of bacteria in air. Pilot-scale bioaerosol reactor experiments that independently measure the solar and nonsolar (absence of solar radiation) inactivation rates of airborne Mycobacterium parafortuitum and Escherichia coli were performed. Direct fluorescent microscopy measurements for total airborne bacteria and culture-based assays were used to measure concentrations in a 1?m3 aerosol reactor that was transparent to UV-A and UV-B wavelengths, and to produce decay curves of airborne bacteria under moderate (50–60%) and high (85–95%) levels of relative humidity (RH). E. coli was more susceptible to airborne decay than M. parafortuitum at all RH levels tested. RH strongly influenced solar and nonsolar airborne inactivation rates in both bacteria. These inactivation rates for both bacteria were greatest at moderate RH levels.     

Experimental and Field Studies of Type I Settling for Particulate Matter Transported by Urban Runoff

Settling velocity is an important constitutive parameter of particulate matter (PM) transported by runoff. Settling velocity is either explicitly or implicitly utilized when designing or modeling unit operations, and in situ or watershed controls for urban rainfall-runoff. Utilizing two common settling devices, a settling column and an Imhoff cone, settling velocities of discrete noncolloidal particles in source area urban rainfall-runoff were measured. A comparison of settling models applicable to discrete (Type I) PM settling was developed. Models were compared to measured results across the noncohesive silt- and sand-size PM gradation from 2 to 2,000?μm, utilizing measured particle-size distributions (PSDs) and specific gravity. Results indicate that Newton’s Law can reproduce measured settling velocity when measured inputs of PM diameter, specific gravity, and temperature are utilized. Alternative models to Newton’s Law (in the Stokesian regime) did not improve agreement with measured settling velocities determined using PSDs from laser diffraction. Settling velocity distributions using Newton’s Law were applied for two limiting classes of storm events loading a screened hydrodynamic separator (HS) at an urban watershed. Results indicate that for a low flow and high flow event, Newton’s Law and a simple ideal overflow model of the HS could reproduce PM separation and the PSD of eluted PM (2 to ～ 250?μm) within 17% of measured results on a gravimetric basis.