Laor Y.,Newe Yaar Research Center |
Parker D.,West Texas A&M University |
Page T.,3333 Queen Mary Rd.
Reviews in Chemical Engineering
The public awareness on environmental odors emitted from industrial, municipal, and agricultural sources has increased over the last decade. Odor regulations continue to be formulated and updated worldwide, and many emitting facilities have been required to address and minimize nuisance odors. The main challenge in the field of odor management is that the measured response is a perception. Nevertheless, it is necessary to quantify the problem in an objective manner using the best available approaches. While the field of odor science has evolved considerably in recent years, there are still different viewpoints and approaches with regard to proper methodologies for measuring and predicting environmental odors. This review aims at providing scientists, engineers, and regulators a balanced and critical understanding of how to respect odor assessments and predictions based on currently existing methodologies and the uncertainties associated with them. Approaches to odor measurement and regulation have varied greatly among local jurisdictions, states, provinces, and countries. Regulatory tools have ranged from relatively simple quantitative measurements of odor and/or specific chemicals to the more complex use of electronic noses and atmospheric dispersion models to predict real-time odor impact on neighboring receptors. Odor measurements are commonly done by means of olfactometry using human panelists. However, as human responses to odor can be subjective and vary among individuals, multiple panelists with tested sensitivities within a controlled range are typically used. Both field and laboratory olfactometry measurements have been used to quantify odors, as each of these is appropriate for different odor magnitudes. Alternatively, odors have been monitored in real time by means of electronic noses, which are arrays of sensors that are correlated based on laboratory olfactometry measurements. Atmospheric dispersion models are often used to predict odor impacts at downwind receptors. Inputs to these dispersion models include odor concentrations measured using olfactometry or electronic noses. Several of the tools used in the field of environmental odors have been adapted from earlier studies on air pollution, but challenges still exist with regard to odor sampling, analyses, and use of prediction models developed for air contaminants. Sampling matters include the use of polymeric bags for sample containment which may release odorous chemicals and may not maintain fully the sample integrity during storage. In addition, sampling protocols vary around the world. Specifically, the sampling of passive area sources with a liquid-gas or solid-gas interface (such as lagoons, manure pits, or compost piles) raises fundamental questions related to the effect of the device used (flux chamber, FC or wind tunnel, WT) on measured odor emission rates. Uncertainties are associated with olfactometry results because of the variability among human panelists. This uncertainty is partly defined by international standards and may be minimized with good laboratory practices. All such uncertainties related to sampling and olfactometry are passed on to real-time monitoring by means of electronic noses, as such noses are calibrated based on olfactometry. While dispersion models of specific air pollutants are based on conservation of mass, the use of these dispersion models for odors merely predicts the number of dilutions needed to reach the perception threshold at a certain distance from the emission source. Such predictions cannot entirely predict odor annoyance unless the relationships between odor concentration and perceived intensity and offensiveness are determined at suprathreshold concentrations. Thus, while great strides have been made in past decades with regard to odor science, there is a need for continued research and an increased understanding of the uncertainties associated with odor monitoring and prediction. Nevertheless, substantial standardization progress has been accomplished that enables researchers and practitioners to address the complex issues related to environmental odor pollution. Best available practices of field sampling, laboratory olfactometry, and modeling can be applied to odor quantification tools and thus minimize and/or account for the uncertainties intrinsic to each tool. The applications of measurement, prediction, and monitoring of odors in the environment are broad, and require effective methodologies to quantify and remediate odor problems in an objective manner. Areas of application include policy development, odor regulation, complaint assessment, odor impact assessment, odor master planning, odor control efficiency assessment, process design, land use policies, and urban planning. Source