John D. Wanjura

DESIGN AND EVALUATION OF A LOW-VOLUME TOTAL SUSPENDED PARTICULATE SAMPLER

The regulation of particulate matter (PM) emitted by agricultural sources, e.g., cotton gins, feed mills, and concentrated animal feeding operations (CAFOs), is based on downwind concentrations of particulate matter less than 10 and 2.5 .m (PM10 and PM2.5) aerodynamic equivalent diameter (AED). Both PM10 and PM2.5 samplers operate by pre-separating PM larger than the size of interest (10 and 2.5 .m) prior to capturing the PM on the filter. It has been shown that Federal Reference Method (FRM) PM10 and PM2.5 samplers have concentration measurement errors when sampling PM with mass median diameters (MMD) larger than the size of interest in ambient air. It has also been demonstrated that most PM from agricultural sources typically have particle size distributions with MMDs larger than 10 .m AED. The PM10 concentration measurement error can be as much as 343% for ambient PM with MMD = 20 .m. These errors are a consequence of the PM10 pre-separator allowing a larger mass of PM greater than 10 .m to penetrate to the filter than the mass of PM less than 10 .m captured by the pre-separator. The mass of the particles greater than 10 .m that are allowed to penetrate to the filter introduces a substantial error in the calculated concentration of PM10. Researchers have reported that sampling PM larger than 2.5 .m AED resulted in a shift in the cutpoint of the pre-separator. If this is true for all PM10 and PM2.5 samplers, then the resulting errors in measurement of ambient concentrations could be even larger. One solution to this problem is to measure the concentration of total suspended particulate (TSP) matter and calculate the concentration of PM10 by determining the mass fraction of PM less than size of interest from the particle size distribution (PSD). The “standard” high-volume TSP sampler operates at a volume rate-of-flow in excess of 1.13 m3 min-1 (40 ft3 min-1). Most of the current PM10 and PM2.5 samplers operate at 1 m3 h-1 (0.589 ft3 min-1). Other researchers reported that TSP samplers have a cutpoint of a nominal 45 .m AED. The U.S. EPA specifies the engineering design parameters for TSP samplers. This article reports the engineering design and evaluation of a low-volume (1 m3 h-1) TSP sampler (TSPLV). The results suggest that the new TSPLV may be more robust and more accurate than the “standard” high-volume TSP sampler.

Evaluation of Modern Cotton Harvest Systems on Irrigated Cotton: Harvester Performance

Picker and stripper harvest systems were evaluated on production-scale irrigated cotton on the High Plains of Texas over three harvest seasons. Observations on harvester performance, including time-in-motion, harvest loss, seed cotton composition, and turnout, were conducted at seven locations with multiple cultivars. In systems where sufficient support equipment was available, strippers had higher productivity (i.e. acres per hour) than pickers. In higher yielding cotton, pickers had a higher productivity rate than strippers. The picker harvest had higher harvest losses but also resulted in lower levels of foreign matter and, therefore, higher turnout. The results of this research have elsewhere been incorporated into an economic model comparing harvest systems under various yield conditions.

COMPARISON OF CONTINUOUS MONITOR (TEOM) AND GRAVIMETRIC SAMPLER PARTICULATE MATTER CONCENTRATIONS

Tapered element oscillating microbalance (TEOM) samplers may offer significant advantages to state air pollution regulatory agencies and air quality researchers in terms of reduced labor and data processing requirements through an automated particulate matter (PM) monitoring system. However, previous research has shown that TEOM samplers may not report accurate PM concentrations due to the operating characteristics of the automated system. This article presents the results of a multiyear study using collocated TEOM and gravimetric samplers configured to measure TSP concentrations from a Texas cattle feedlot. The objective of this work was to define the relationship between PM concentrations measured by TEOM and gravimetric samplers and characterize the influence of concentration intensity and particle size on that relationship. The results show that there was a significant positive linear relationship between the concentrations measured by the TEOM and gravimetric TSP samplers (p-values < 0.001). It was observed that in general, the TEOM samplers reported lower TSP concentrations than the collocated gravimetric TSP sampler. Further investigation into these results indicated that the difference in the concentration measured by the TEOM sampler versus the gravimetric TSP sampler (known as the TEOM measurement error) is correlated with the concentration measured by the gravimetric TSP sampler, but the nature of that relationship varies by location. However, linear relationships were observed between the measurement error of the TEOM samplers and the mass median diameter and geometric standard deviation of the collocated gravimetric TSP sample.

Soil Moisture Sensing via Swept Frequency Based Microwave Sensors

There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications.

Evaluation of modern cotton harvest systems on irrigated cotton: fiber quality

Picker and stripper harvest systems were evaluated on production-scale irrigated cotton on the High Plains of Texas over three harvest seasons. Observations on fiber quality using High Volume Instrument (HVI) and Advanced Fiber Information Systems (AFIS) were made on multiple cultivars harvested from six locations. When fibers were relatively immature, micronaire, length, and length uniformity as measured by HVI were better for picker harvested cotton than for stripped cotton leading to a higher loan value and average sale price for the producer. In cases where fibers were more mature, differences in fiber quality parameters between picked and stripped cottons were less pronounced leading to less discrepancy in the value of cotton harvested. However, differences in nep counts, short fiber content, and visible foreign matter between harvest treatments were still distinguishable. The results of this study indicate that producers may realize greater fiber quality and lint value by using picker harvesters, but the magnitude of those differences are a function of growing conditions and/or fiber maturity. Differences in cultivars also played a large role in determining fiber properties.

Estimating FRM PM10 Sampler Performance Characteristics Using Particle Size Analysis and Collocated TSP and PM10 Samplers: Cotton Gins

In the U.S., regional air quality compliance with national ambient air quality standards (NAAQS) for particulate matter (PM) is based on concentration measurements taken by federal reference method (FRM) samplers. The EPA specifies the performance criteria for the FRM samplers. These criteria for the FRM PM10 samplers are defined as a cutpoint and slope of 10 ±0.5 µm and 1.5 ±0.1, respectively. It is commonly assumed that the performance characteristics of the FRM PM10 sampler do not vary and are independent of the PM characteristics. Several sources have observed errors in the concentrations measured by the FRM PM10 samplers and have suggested that shifts in the sampler performance characteristics may lead to the observed concentration measurement errors. Limited work has been conducted on quantifying the shift in the performance characteristics of the FRM PM10 sampler operating under field conditions. Recent work at a south Texas cotton gin showed that true PM10 concentrations were 55% of the concentrations measured by the FRM PM10 sampler. If the FRM PM10 sampler were operating within the performance criteria range specified by the EPA, then the true concentrations would be within approximately 12% of the concentrations measured by the FRM PM10 sampler. The focus of this work was to quantify the shifts in the cutpoint and slope of the penetration curve of the FRM PM10 sampler. Results show that the cutpoint and slope of the FRM PM10 sampler shifted substantially and ranged from 13.8 to 34.5 µm and from 1.7 to 5.6, respectively, when exposed to large PM as is characteristic of agricultural sources. These shifts in the cutpoint and slope of the FRM PM10 sampler resulted in overestimation of true PM10 concentrations by 145% to 287%.

PERFORMANCE CHARACTERISTICS OF A LOW-VOLUME PM10 SAMPLER

Four identical PM10 pre-separators, along with four identical low-volume (1 m3 h-1) total suspended particulate (TSP) samplers were tested side-by-side in a controlled laboratory particulate matter (PM) chamber. The four PM10 and four TSP samplers were also tested in an oil pipe cleaning field to evaluate the PM10 samplers’ performance characteristics. The PMs used in the chamber tests had mass median diameters (MMDs) larger than 10 .m, whereas the PM emitted from the oil pipe cleaning system for the field tests had MMD smaller than 10 .m. The co-located TSP and PM10 sampler testing results indicate that PM10 samplers over-sample when exposed to ambient PM having MMD larger than 10 .m aerodynamic equivalent diameter (AED) and under-sample when exposed to ambient PM with MMD smaller than 10 .m. The over-sampling and under-sampling rates varied with the change of MMD and the PM loading (TSP concentration). The cutpoints and slopes of the PM10 pre-separator changed with the change of MMD of inlet PM.

A SIMULATED APPROACH TO ESTIMATING PM10 AND PM2.5 CONCENTRATIONS DOWNWIND FROM COTTON GINS

Cotton gins are required to obtain operating permits from state air pollution regulatory agencies (SAPRA), which regulate the amount of particulate matter that can be emitted. Industrial Source Complex Short Term version 3 (ISCST3) is the Gaussian dispersion model currently used by some SAPRAs to predict downwind concentrations used in the regulatory process in the absence of field sampling data. The maximum ambient concentrations for PM10 and PM2.5 are set by the National Ambient Air Quality Standard (NAAQS) at 150 .g/m3 and 65 .g/m3 (24 h average), respectively. Some SAPRAs use the NAAQS concentrations as property line concentrations for regulatory purposes. This article reports the results of a unique approach to estimating downwind PM10 and PM2.5 concentrations using Monte Carlo simulation, the Gaussian dispersion equation, the Hino power law, and a particle size distribution that characterizes the dust typically emitted from cotton gin exhausts. These results were then compared to a 10 min concentration (C10) and the concentrations that would be measured by an FRM PM10 and PM2.5 sampler. The total suspended particulate (TSP) emission rate, particle size distributions, and sampler performance characteristics were assigned to triangular distributions to simulate the real-world operation of the gin and sampling systems. The TSP emission factor given in AP-42 for cotton gins was used to derive the PM mass emission rate from a 40 bale/h plant. The Gaussian equation was used to model the ambient TSP concentration downwind from the gin. The performance characteristics for the PM10 and PM2.5 samplers were then used to predict what the measured concentration would be for two PSD conditions. The first PSD assumption was that the mass median diameter (MMD) and geometric standard deviation (GSD) were constant at 12 .m and 2, respectively, and the second scenario assigned a triangular distribution to the MMD and GSD of {15, 20, 25} .m and {1.8, 2.0, 2.2}, respectively. The results show that the PM2.5 fraction of the dust emitted under either PSD condition was negligible when compared to the NAAQS for PM2.5 of 65 .g/m3. The results also demonstrate that correcting for wind direction changes within the hour using the power law reduces the ambient concentration by a factor of 2.45.

Influence of Harvesting and Gin Cleaning Practices on Southern High Plains Cotton Quality

Southern High Plains cotton has improved over the last ten years with regard to yield and fiber length and strength. In light of increased adoption of picker harvesting to preserve fiber quality and improve harvest productivity, ginning practices are needed which preserve fiber quality and maximize return to the producer. The objective of this work was to investigate the influence of harvest method, number of seed-cotton extractor cleaners (e.g. stick machines), and seed-cotton cleaning rate on foreign matter content, lint value, and fiber and yarn quality of cotton produced in the Southern High Plains. Compared to using only one stick machine, the use of two stick machines in the seed-cotton cleaning system removed more foreign material from both picker- and stripper-harvested cotton, but more foreign material was removed by the stick machines from stripper-harvested cotton because it had higher initial foreign matter content. Seed-cotton cleaning rate had no influence on stick machine cleaning performance for picked cotton but higher cleaning rates reduced stick machine cleaning performance for stripper-harvested cotton. Picker-harvested cotton exhibited improved HVI and AFIS fiber quality and higher bale values compared to stripper-harvested cotton. The use of two stick machines improved fiber color properties and reduced lint foreign matter content. Seed-cotton cleaning rate had a minimal effect on fiber quality and bale value was not influenced by the number of stick machines or seed-cotton cleaning rate. Total lint value, on a production area basis, was higher for stripper-harvested cotton after both lint cleaners compared to picker-harvested cotton due to yield differences. Yarn imperfections were reduced for ring spun yarn produced from picker-harvested cotton processed through one stick machine at the high cleaning rate. The findings of this work support a recommendation for using one stick machine in seed-cotton cleaning systems processing picker-harvested cotton and two stick machines in systems processing stripper-harvested cotton.

Fringe capacitance correction for a coaxial soil cell.

Accurate measurement of moisture content is a prime requirement in hydrological, geophysical and biogeochemical research as well as for material characterization and process control. Within these areas, accurate measurements of the surface area and bound water content is becoming increasingly important for providing answers to many fundamental questions ranging from characterization of cotton fiber maturity, to accurate characterization of soil water content in soil water conservation research to bio-plant water utilization to chemical reactions and diffusions of ionic species across membranes in cells as well as in the dense suspensions that occur in surface films. One promising technique to address the increasing demands for higher accuracy water content measurements is utilization of electrical permittivity characterization of materials. This technique has enjoyed a strong following in the soil-science and geological community through measurements of apparent permittivity via time-domain-reflectometry (TDR) as well in many process control applications. Recent research however, is indicating a need to increase the accuracy beyond that available from traditional TDR. The most logical pathway then becomes a transition from TDR based measurements to network analyzer measurements of absolute permittivity that will remove the adverse effects that high surface area soils and conductivity impart onto the measurements of apparent permittivity in traditional TDR applications. This research examines an observed experimental error for the coaxial probe, from which the modern TDR probe originated, which is hypothesized to be due to fringe capacitance. The research provides an experimental and theoretical basis for the cause of the error and provides a technique by which to correct the system to remove this source of error. To test this theory, a Poisson model of a coaxial cell was formulated to calculate the effective theoretical extra length caused by the fringe capacitance which is then used to correct the experimental results such that experimental measurements utilizing differing coaxial cell diameters and probe lengths, upon correction with the Poisson model derived correction factor, all produce the same results thereby lending support and for an augmented measurement technique for measurement of absolute permittivity.