Christopher G. Henry

Modeling Odor Dispersion From a Swine Facility Using AERMOD

Meteorological conditions, odor emissions, and ambient odor levels at a four-barn, swine finishing facility in Iowa were measured in the summer and fall of 2004. This paper compares ambient odor levels measured using a Nasal Ranger® compared to those predicted by AERMOD, a relatively new air dispersion model. Scaling factors needed to adjust predicted odor levels to those observed ranged from 1.66 to 3.12, depending on the source configuration used by the model. Predicted odors levels from the point source configuration required the smallest scaling factor (1.66) and accounted for the greatest percentage of variability in the data when compared to Nasal Ranger readings.

COMPARISON OF AMBIENT ODOR ASSESSMENT TECHNIQUES IN A CONTROLLED ENVIRONMENT

This article compares results of using dynamic triangular forced-choice olfactometry (DTFCO), the Mask Scentometer, the Nasal Ranger, and an odor intensity reference scale (OIRS) to assess odors in a controlled-environment chamber in the Iowa State University Air Dispersion Laboratory. The methods were used to assess 13 odor levels in the chamber. Swine manure mixed with water was used to vary the odor levels. DTFCO did not correlate well to the other ambient odor assessment methods. Predicting dilution to threshold (D/T) using intensity ratings compared to using intensity ratings directly degraded the coefficient of determination (Ro 2 ) through zero with the other methods in all cases. Average intensity-predicted D/T, the Mask Scentometer, and the Nasal Ranger correlated well with each other, with strong Ro 2 values (greater than 0.85) and regression slopes near 1, and the session means were not found to be significantly different ( = 0.05). Using the geometric means of the device D/T settings, (D/T)G, improved the Ro 2 values between the other methods and the Nasal Ranger and Mask Scentometer. Average intensity-predicted D/T values were three to four times higher than Nasal Ranger assessment ((D/T)G and D/T, respectively), and Nasal Ranger (D/T)G was roughly five times higher than Mask Scentometer (D/T)G.

Downwind Odor Predictions from Four Swine Finishing Barns Using CALPUFF

A collaborative research effort by several institutions is investigating odor emissions from swine production facilities, and the impacts of those emissions on farm neighbours. Trained human receptors were used to measure the downwind odor concentrations from four tunnel ventilated swine barns near Story City, Iowa. Twenty-six measurement events were conducted between June and November 2004 and modeled using a specially coded short time-step version of CALPUFF to predict short time step durations. Source emission measurements and extensive meteorological data were collected along with ambient olfactometry analysis using the Nasal Ranger™ device (St. Croix Sensory, St. Paul MN). Approximately 64% of measured odor generally falls within the range of modeled values. Analysis of measured odor concentration and corresponding meteorology indicate that maximum ambient odor impacts occur with lower ambient temperature during non-turbulent conditions. Analysis of the data set did not yield a strong relationship directly (R2=0.33), but a regression analysis indicated that the modified CALPUFF model yielded a slope or scaling factor of 0.99, indicating overall a good relationship between model and observed. However, when the data is tested with the Spearman’s rank correlation coefficient an rs of 0.17 was calculated, indicating a poor rank correlation and was not significant (p=0.05). Statistical analysis is inconclusive as to whether the results have bias, but indicate large error in the results. Given that there were no scaling or peak to mean ratio adjustments to the model predictions, the results are very promising for predicting odors using CALPUFF.

The Economic Impacts of Various Public-Policy Scenarios for Methane Recovery on Dairy Farms

The feasibility of anaerobic digesters for dairy and swine operations in Nebraska was evaluated using EPA’s Ag Star software program Farmworks 2.0 (1997) and local values for farm energy costs, mainly electricity. Four incentive programs were considered that would subsidize anaerobic digestion. Installation of a digester system is a significant investment that is currently very difficult to justify economically to Nebraska producers based upon consideration of readily quantifiable income and expenses, regardless of farm size. Larger dairy operations looking to invest in this technology would benefit most from a tax credit and/or subsidized electricity sales, policies that relate directly to the production of electricity. On the other hand, small dairy farms likely would benefit more from a no-interest loan or a cost-share program – policies that relate directly to the capital cost incurred. Larger operations are more likely to place a value on odor control and would experience a lower unitized effective cost than smaller operations. The effective cost may still be unwieldy in an industry with tight profit margins, however.

Ground Truthing CALPUFF and AERMOD for Odor Dispersion from Swine Barns using Ambient Odor Assessment Techniques

A collaborative research effort by several institutions investigated the dispersion of odors from a swine production facility. Trained human receptors measured downwind odor concentrations from four tunnel-ventilated swine finishing barns near Story City, Iowa, during twenty measurement events conducted between June and November 2004. Odor concentrations were modeled for short time steps using CALPUFF and AERMOD atmospheric dispersion models to compare predicted and measured odor levels. Source emission measurements and extensive micrometeorological data were collected along with ambient odor measurements using the Nasal Ranger® device (St. Croix Sensory, St. Paul MN), Mask Scentometer, odor intensity ratings, and air sample analysis by dynamic triangular forced-choice olfactometry (DTFCO). AERMOD predictions fit the odor measurements slightly better than CALPUFF with predicted concentrations being about half those predicted by CALPUFF. The Mask Scentometer and Nasal Ranger® measurements related best to the dispersion model output, and scaling factors of 3.0 for CALPUFF and 2.4 for AERMOD suggested for the Nasal Ranger® and 0.5 for the Mask Scentometer (both models). Measurements obtained using the Nasal Ranger®, Mask Scentometer, and odor intensity ratings correlated well to each other, had the strongest linear relationships, and provided slopes (measured: modeled) closest to 1.0. Converting intensity ratings to a dilution to threshold concentration did not correlate and relate as well, and this method was deemed less desirable for ambient odor assessment. Collection of ambient air samples for analysis in a olfactometry laboratory displayed poor correlations with other methods and should not be used to assess ambient odors.

Mask Scentometer for Assessing Ambient Odors

This paper summarizes the development and operation of a Mask Scentometer and reports air dilution ratios measured during its use, which were used to establish the device’s dilution-to-threshold settings. The Mask Scentometer is a facial respirator that has been modified to operate conceptually like the Barneby and Sutcliffe Box Scentometer. The Mask Scentometer is comprised of a ¼-face respirator with two modified spin-on cartridges, one per side, which facilitate mixing ambient air with filtered air for presentation to an odor assessor at user-selected dilution ratios. The flow-weighted average dilution ratios produced within the Mask Scentometer were 18, 4.5, 2, 1, and 0.35. Investigators using the Mask Scentometer to measure ambient odor concentrations are advised to use these dilution-to-threshold values.

Association of Odor Measures with Annoyance: An Odor-Monitoring Field Study

Multiple assessments of ambient odor were made by trained individuals in the vicinity of a swine finishing operation in eastern Nebraska during the summers of 2005 and 2006. This paper addresses an analysis of assessor responses in Year 1 of this field study to determine what relationships existed between field odor measurements/ratings and ratings of annoyance potential, and to identify candidate measurement threshold values for odors that are likely to cause an annoyance. The first-year results showed that the likelihood of odor causing annoyance increased as ambient odors became more offensive, more intense, and more concentrated, with r2 values of 0.89, 0.81, and 0.64, respectively. Selection of threshold values for predicting annoyance depends on the extent of annoyance to be considered. In this analysis, candidate thresholds were sought to delineate both ‘any degree of stated annoyance’ and ‘consequential annoyance’ – defined as a state of odor that would likely invoke a change in behavior or activity level by the receptor and instill some memory of the odor event afterwards. Based upon the first-year results of this study, candidate thresholds for any stated annoyance and consequential annoyance, respectively, appear to be: 1 and 2 for intensity (on a 0-5 scale); 2 D/T and 7 D/T for odor concentration (as measured using a mask scentometer; and -1 and -2 for Hedonic tone (on a +4 to -4 scale). Further study is needed to verify these threshold values with other operations and animal species, as well as to clarify the relationship between odor intensity and concentration when measured in the field.