Kenneth E. Noll

A fundamental analysis of the isotherm for the adsorption of phenolic compounds on activated carbon

The Freundlich isotherm has been widely used in the design of activated-carbon adsorption processes. The isotherm is easy to use and is applicable to a wide spectrum of organic compounds and adsorbents. The main drawback for the isotherm is that it is an empirical formula requiring experiments to determine its coefficients. To alleviate this drawback, a procedure is developed in this study to correlate the Freundlich coefficients with the basic properties of three components involved in adsorption (adsorbate, adsorbent and solvent). Chloro- and nitrophenols were used as the test adsorbates, and granular activated carbon (GAC) was used as the adsorbent. The isotherm data showed that the percentage of the GAC pore surface covered by phenolic molecules was a better measurement for the amount adsorbed than the traditional mass-based solid concentration. A solution concentration normalized with respect to the solubility of the phenolics was used to account for the effects of phenol-water interactions. Isotherms of surface coverage versus normalized concentration conformed very well to a modified Freundlich model. The modified Freundlich exponent (1/n′) was found to have an inverse linear relationship with the electron density of phenolics calculated from molecular orbital theory. The correlation will allow the prediction a priori of 1/n′ from the molecular structures of the adsorbate and adsorbent.

Characterization of the deposition of particles from the atmosphere to a flat plate

Abstract The airborne concentration of coarse particles ( > 1 μm diameter) was measured with a Rotary Impactor simultaneously with the measurement of particle dry deposition flux with a smooth surrogate surface with a sharp edge, mounted on a wind vane. The deposition surface was designed to provide minimum air flow disruption and thus provide an estimate of the lower limit for dry deposition flux. The deposited particles were weighed and counted. Microscopic count data generated the size distribution of particles collected on the deposition plate. The results demonstrated that 99% of the mass deposited on the plate was due to particles > 2 μm diameter. Because the measured dry deposition mass was due to atmospheric coarse particles and the measured airborne concentration was also due to coarse particles, the two data sets were combined to evaluate the dynamics of atmospheric coarse particle deposition. Deposition velocity was calculated by dividing the particle flux by the airborne coarse particle concentration. The deposition flux was 3.0 μg m −2 s −1 for 17 samples taken over a 1-month period in an urban area. The deposition velocity averaged 11.7cm s −1 . The deposition flux, deposition velocity and coarse particle Mass Median Diameter (MMD) were all shown to increase as wind speed increased. There was a large difference between day and night samples. Night samples had lower airborne concentrations (47%), lower deposition flux (65%) and lower deposition velocities (40%). These differences were accompanied by a 47% decrease in wind speed and a 30% decrease in the MMD of airborne coarse particles. This is in agreement with deposition model results where deposition velocity decreases when wind speed and particle size decrease.

Dry Deposition Velocities as a Function of Particle Size in the Ambient Atmosphere

The atmospheric particle mass size distribution (0.1–100 μ m) and dry deposition flux were measured simultaneously with a wide range aerosol classifier (WRAC) and a smooth greased surface. Microscopic techniques were used to size the particles collected on the deposition surface and generate mass size distributions of deposited particles. All the depositional mass size distributions peaked (interval with the largest mass) between 30 and 100 μm in diameter. Deposition velocities were calculated by dividing the size segregated particle flux by the airborne particle concentration for each of the 10 WRAC stage intervals. Experimentally determined dry deposition velocities for atmospheric particles in the size range of 5–80 μm in diameter were greater than predictions made with the Sehmel-Hodgson deposition velocity model developed from wind tunnel experiments, particularly at higher wind speeds. A multistep method was used to calculate total and cumulative deposition fluxes with the Sehmel-Hodgson model. Calc...

Development of a dry deposition model for atmospheric coarse particles

Atmospheric inertial deposition of coarse particles has been quantified by the evaluation of particle dry deposition flux data collected simultaneously on the top and bottom surfaces of a smooth plate with a sharp leading edge that was pointed into the wind by a wind vane. The deposited particles were weighed and counted. The airborne concentration of coarse particles was measured with a Rotary Impactor. Deposition velocity was determined by dividing the mass flux (plate) by the airborne concentration (Rotary Impactor). The deposition velocity was considered to be due to gravitational settling (VST) and inertial deposition (VI). Deposition to the upper plate surface (VdU) was given by: VdU = VST + VI, while deposition to the lower plate surface (VdL) was given by: VdL = − VST + VI. The inertial deposition velocity was defined as: VI = \geAU∗, where \geA is the particle effective inertial coefficient and U∗ is friction velocity. Based on these equations, \geA was evaluated as a function of particle size as: \geA = 1.12e−30.36/dn, where da is the particle aerodynamic diameter (μm). The correlation coefficient was 0.92, \geA varied from 0.1 to 1.0 for particles between 5 and 100 μm diameter. The particle dry deposition fluxes obtained for the top and bottom surfaces of the plate were extended to the free atmosphere. A particle flux ratio (FR) was defined as: FR = VdLVdU. The mass median aerodynamic diameter MMDa for the atmospheric coarse particle size distribution correlated closely with the geometric mean values of (FR). The flux ratio was also related to the shape of the coarse particle mass distribution. The flux ratio was less than 0.1 for particles smaller than 3 μm diameter and did not increase significantly with wind speed. This corresponded to a minimum in the coarse particle mass distribution that was present for particles smaller than 3 μm diameter. The flux ratio was also small for particles larger than 50 μm diameter but increased rapidly with wind speed. This indicated that larger particles could remain suspended under high wind speed conditions. The measured mass distributions for atmospheric coarse particles showed an increase in larger particles with an increase in wind speed. This was in accordance with the increase in the particle flux ratio.

Comparison of atmospheric coarse particles at an urban and non-urban site

Abstract This paper provides an evaluation of 90 coarse particle mass distributions taken over a 15-month period during 1983–1984 at an urban and a nearby non-urban site located in the midwestern United States. The coarse particles (> 5μm diameter) were sampled in four mass fractions (6–11, 11–20, 20–29, > 29 μm diameter) with the Noll Rotary Impactor. Diurnal and seasonal differences were measured. Samples were collected when the ground was dry, wet and frozen. The shape of the mass distribution was similar for most samples and was well represented by a log-normal distribution. The mass median diameter varied between 15 and 30 μm with an average near 20 μm diameter. The geometric standard deviation average was 2.0. Urban samples had 75 percent more total mass than nonurban samples. At the urban site, concentrations were 50 percent higher during mid-day than at night. Dry ground samples were 30 percent higher than wet ground and 90 percent higher than frozen ground samples. The mass median diameter (MMD) was dependent on friction velocity ( U ∗ , cm s−1), where MMD = 0.212 U ∗ + 15.7. The correlation coefficient between the two variables was 0.69.

Characterization of large particles at a rural site in the eastern United States: Mass distribution and individual particle analysis

Abstract A unique combination of an effective sampler and analysis of individual particles has been used in studying large particles (> 5 μm) at a rural site in eastern United States. The sampler is a modified ‘high volume’ rotary inertial impactor, which consists of four collectors of different widths, rotating at high speed and collecting particles by impaction. The collector surfaces were Mylar films coated with apiezon to ensure retention. After sampling, the collection surfaces were weighted to obtain the mass-size distribution. A section of the Mylar sample was transferred to a scanning electron microscope to study in detail the morphology and elemental content of individual particles. Results from two case studies indicated the following conclusions could be made: 1. (a) Natural sources, minerals and biologicals, were the main contributors to large particles (> 5 μm), 2. (b) Contribution of anthropogenic sources, mainly coal-fired power plants emitting fly ash particles, was limited to a few percent of the 5–10 μm size range, 3. (c) Pollen and some of the minerals were enriched in sulfur, probably as accumulation of sulfate on the particle surface, 4. (d) At low wind speeds the anthropogenic contribution was enhanced, whereas at high wind speeds natural sources were almost the only contributors to the large particle mode. In both cases the mass distribution of the large particles peaked at around 15 μm.

A comparison of dry deposition modeled from size distribution data and measured with a smooth surface for total particle mass, lead and calcium in Chicago

For 11 sampling periods, atmospheric particle and elemental (Pb, Ca) mass size distributions (0.1–100 μm diameter) were measured with a Noll Rotary Impactor (NRI) and cascade impactor in Chicago, Illinois. The NRI and cascade impactor measurements were continuous; there was no displacement in the bimodal size distributions. Lead, a primarily anthropogenic element, tended to be associated with the fine-particle mode (< 2.5 μmdiameter); Ca, a primarily crustal element, was associated with the coarse particle mode (< 2.5 μmdiameter). Atmospheric dry deposition fluxes were simultaneously measured with a specially designed and constructed smooth surface pointed into the wind. A particle dry deposition velocity model was used in conjunction with the measured sized distributions to calculate dry deposition fluxes, which were then compared to the measured fluxes. The method, which combined a 12-step flux calculation with the particle dry deposition velocity model, agreed with the measured flux data to within a factor of two. The modeled cumulative fluxes show that fine particles are responsible for only a small fraction of the dry deposition flux. The per cent of the modeled flux due to particles less than 2.5 μm was 0.06, 0.5 and 0.06% for particle mass, Pb and Ca, respectively. The results indicate that atmospheric dry deposition is dominated by coarse particles due to their high deposition velocities.

Comparison of three methods to predict adsorption isotherms for organic vapors from similar polarity and nonsimilar polarity reference vapors

Abstract The Polanyi-Dubinin equation was used to predict adsorption isotherms for eight organic vapors at 25°C and for two organic vapors at 25°C, 40°C and 60°C on activated carbon in this analysis. The theoretical affinity coefficient, β, is calculated by three methods (molar volume, molecular parachor, and electronic polarization) based on nonpolar and polar reference vapors. The corresponding experimental isotherm data were measured by gravimetric method. Comparison between calculated and experimental isotherm data showed that 1. (1) for optimum isotherm prediction, the reference vapor should have similar polarity to the vapor whose adsorption is being predicted, 2. (2) after choosing an appropriate reference vapor, there is essentially no difference in the accuracy of the isotherm predictions by the three methods, and 3. (3) the molar volume method is more applicable for predicting isotherms at different temperatures.

Atmospheric coarse particulate concentrations and dry deposition fluxes for ten metals in two urban environments

The atmospheric coarse particle concentrations of ten metals (Al, Ca, Cd, Cu, Fe, Mn, Ni, Pb, Si and Zn) were measured with the Noll Rotary Impactor (NRI) in the Los Angeles Basin (Claremont) California, and in Chicago, Illinois. The dry deposition fluxes were also measured for the ten elements at the Chicago site. An evaluation of the data demonstrates that the coarse particle mass could be divided into two categories: (1) material that was primarily of crustal origin (Al, Ca, Fe and Si) and (2) material that was primarily of anthropogenic origin (Cd, Cu, Mn, Ni, Pb and Zn). The mass of crustal material varied between 15 and 50% of the total coarse particle mass, while the mass of anthropogenic material was <1%. The dry deposition fluxes for the crustal material were between 20 (Al) and 200 (Si) ng m−2 s−1 while the fluxes for the anthropogenic material were between 1 and 7 ng m−1 s−1 for Cu, Mn, Pb and Zn. The cadmium (Cd) flux averaged 0.02 ng m−2 s−1.

Design methodology for optimum dosage air monitoring site selection

Abstract An air monitoring site selection procedure has been developed that ranks potential air monitoring sites according to their ability to represent the ambient dosage (i.e. the product of the concentration by exposure time) pattern in a monitoring network. The Dosage Monitoring Survey Design (DMSS) analyzes the dosage impact at grid receptors by dispersion modeling. High-dosage grids become potential monitoring sites. The uniqueness of DMSS is the introduction of a cluster of contiguous grid receptors that exceed a threshold value. One station is assigned to the cluster, thus eliminating redundancies among adjacent high dosage grids. The site selection procedure specifies locations for high-dosage monitoring stations along with the cluster area capabilities of each station. An efficiency term based on the ratio of a stations dosage measuring capabilities to the total dosage in the network provides a method of ranking stations. An analysis of the design procedure shows that as the threshold concentration decreased the distance from the source where the maximum dosage was found increased and there was a slight increase in station efficiency. Also, as averaging time increased, higher efficiencies were achieved for individual stations.