UCLA

Odor complaints have become the majority of all air quality complaints in recent years. Evaluating an odor nuisance requires sensory analyses to determine the cause of the problem; and chemical analyses to control the problem since chemicals cause odors. The best choice of sensory methods is the Odor Profile Method (OPM), using an Odor Wheel to identify the odor(s). The best choice of chemical analysis is based upon the chemicals that caused the perceived odors and were identified by the odor wheel.

The OPM can determine odor character, intensity, frequency, and duration for each odor within an odorous mixture at a specific time and location. The OPM is based upon the Weber-Fechner law that states:Odor Intensity = k Log (concentration of the chemical(s) causing the odor) + b

Persistency curves can determine odor persistence upon dilution. Persistency curves include two types, the Weber-Fechner Curve and the Odor Dilution Curve. Weber-Fechner curve indicates the persistence of each odorous compound and the Odor Dilution Curve indicates the persistence of each odor type that are perceived in an odor mixture.An odor panel using the OPM has successfully evaluated if the closure of a Landfill from 6-9 AM has minimized the odor complaints related to this Landfill. The OPM results have shown the odor characters of the possible odors produced by the Landfill to be rancid, rancid-sweet, rotten vegetable, and sewery/fecal. The intensities of these odor characters were between 1 - 4. Only 1.3% of the samples produced an odor related to the Landfill, and the duration of odor events was all less than 40 minutes. Reproduction of the Weber-Fechner curves of the selected six odorants was done by four panelists. The determined Weber-Fechner curves were similar to the previous study, but the regression lines were not identical. The determined Weber-Fechner curves were used as the reference for the same panelist to understand odor persistency at the Energy Development Facility. The Odor Dilution Curve at the EDF biofilter confirmed the information provided by the Weber-Fechner curves. The musty odor (caused by IPMP, MIB etc.) dissipates slower than the fecal odor (caused by skatole, indole, etc.) and the sulfur odor (caused by dimethyl sulfide, dimethyl disulfide, etc.). The masking effect that the musty odor was covered by sulfur odor and fecal odor also can be explained by the cross-over of Weber-Fechner curves. The slope, k of the Weber-Fechner curves upon dilution of each odor type using the OPM method can provide an insight into the persistency of each specific odorant. This information was used to evaluate the performance of an odor masking agent. Lower k value, higher application concentration or application at a further distance of the masking agent might solve the poor performance of the odor masking agent. An odor attribution study was conducted to evaluate three facilities: an Energy Development Facility, a Resource Recovery Park and a Wastewater Treatment Plant. Results of the OPM data only shown one out of three facilities has consistency between the air sample from the inside locations of the facility with the air sample from the downwind location. The Odor Dilution Curve results showed that with higher dilution ratios, most of the odor characteristics disappeared. However, in some locations, the Odor Dilution Curve showed the unmasking effect of musty odor. The musty odor was not detected at the OPM level or at the lower dilutions but started to appear after the higher intensities of fecal, rancid or rotten vegetable odor have disappeared. The Odor Dilution Curves successfully predict odor types that were not shown buy the OPM. The comparison of the Odor Activity Value data and the OPM data proved that OPM as a sensory method works well on telling odor characters and intensities. However, not all the data correlate with each other due to the unknown synergistic or antagonistic effect for odor mixtures. Above all, it has been proved that using only chemical analysis or only odor sensory data is not enough. The combination of the two should be performed for any type of odor attribution study. The OPM have provided predictions on odor nuisances from the source level, the Weber-Fechner curves have provided predictions on the persistence of an odorant and gave valuable suggestion on masking agent selection. Odor Dilution Curves have provided odor predictions at the level of the receptors. This thesis, for the first time, have used the OPM, the Persistency Curves and the combination of the two to evaluate odor nuisance.