Sensory Measurement of Ambient Traffic Odors

Laboratory determinations of ambient traffic odors were conducted in the streets of Stockholm. The measurements were made with a sensory method based on signal detection theory. The occurrence of odors was expressed by an index of detectability (d′) which was compared to the ambient carbon monoxide concentration and the rhythm of the traffic. The results showed that the detection technique employed could well be adjusted to field conditions by use of a mobile odor laboratory. Also, the odor index (d′) was correlated with other parameters in the trafficked environment in the expected way. The odorous emissions are likely to be diluted quickly as distance from the street increases. However, the relevance of the index of detectability as a measure of dose and response needs to be studied further.     

Odor Thresholds by Forced-Choice Dynamic Triangle Olfactometry: Reproducibility and Methods of Calculation

The reproducibility of odor thresholds determined by forced-choice dynamic triangle olfactometry was studied employing panels of 23- 45 subjects who tested 12 odorants, with four replications for one (1-butanol). Depending on the selection of panelists, their number, and between-session differences in olfactometer variables, the standard deviation of log(threshold) values ranged from 0.12 (same session, different panels of nine) to 0.37 (different sessions, different panels of nine).

Among the demographic factors, only age was found significant; those below age of 30 were 1.6-3 times more sensitive than the older group. No systematic sensitivity difference was found between females and males, and nonsmokers and smokers.

Suspicion has been raised in the literature that the method used here, ASTM E679, yields biased results. It is shown for panels of 6-45 members that such biases are inconsequential if the range of concentration presented to the panelists is large enough, and the group threshold is well within that range. The Hall-Ellis method of calculation may have a slight advantage for panels of less than eight subjects, but such small panels are not advisable because of their high variability. The method based on the detectability index exhibited more scatter and would need an impracticaliy large number of measurements.     

Measurement of Ozone Concentrations in Ambient Air Using a Badge-Type Passive Monitor

Abstract

A badge-type passive monitor was used to evaluate the effectiveness of four ozone trapping reagents for measuring O₃ concentrations in the air. These were sodium nitrite (NaNO₂), 3-methyl-2-benzothiazolinone acetone azine (MBTH), p-acetamidophenol (p-ATP), and indigo carmine. Experiments in an exposure chamber showed that only NaNO₂ and MBTH monitors gave sensitive and linear responses over realistic ranges of O₃ concentrations. When tested in ambient air, NaNO₂ and MBTH monitors with a single-layer diffusion barrier overestimated O₃ concentrations by a significant amount. This was largely canceled out in the NaNO₂ monitor by using a multi-layered diffusion barrier to combat wind turbulence effects. However it had almost no effect on the MBTH monitor, and it was found that NO₂ was a source of serious interference. We concluded that using the NaNO₂ monitor with an effective diffusion barrier can measure O₃ in ambient air with an accuracy of ±16%.     

Measurement of Ambient Ground-Level Concentrations of Hydrogen Fluoride

The use of published, accepted methods for measuring ambient levels of gaseous hydrogen fluoride (HF) with a double-tape sampler led to large errors. The major source of error was found to be scrubbing In the stainless steel intake, which was avoided by substituting Teflon for the stainless steel. To avoid this and other problems encountered in the measurement of HF, we revised the double-tape sampler method and modified the double-tape sampler. We designed and constructed an HF calibrator for use in testing the revised method and modified sampler In the field and laboratory.

The results of a round robin indicated that, in the laboratory, the revised method has a single-operator precision of 3 percent at 2.6 μg/m³ and a between-laboratory precision of 4 percent. The average bias at 2.6 μg/m³ was 0.02 μg/m³ and was not significantly different from zero. Comparable precision and accuracy were obtained in the field. The response was linear, at least to 10 μg/m³. The limit of detectability, which appears to be limited by the variability in measurements of blank tapes, is 0.07 μg/m³. The revised method appears both precise and accurate.     

Derivation,Application and Interrelationship of Ambient Noise Measurement Parameters

A study was undertaken to determine the rationale and justification for the profusion of schemes proposed for the purpose of quantifying non-impulsive ambient noise levels. The study explored the multiplicity of noise measurement parameters involved in significant control strategies. This paper presents the highlights of the study. Derivations are provided for typical parameters, weighted and unweighted, objective and subjective. The application of significant noise measurement techniques is explained in enough detail to impart understanding of complex methodology. Judgments relative to the necessity for this complexity are left largely to the reader. Many of the noise control schemes studied are interrelated. Such techniques as time and frequency weighting are employed to derive new parameters from existing ones. Approximate conversion factors are presented in this paper to enable the reader to get back and forth between compatible systems. The results of the study indicate, as the paper concludes, that uniform noise control legislation is necessary. To be most effective, noise control parameters should be expressed in terms to which the lay public can relate and which do not require an expensive black box to measure.     

Prediction of Ambient PM10 and Toxic Metals Using Artificial Neural Networks

Abstract

In this study, an artificial neural network is employed to predict the concentration of ambient respirable particu-late matter (PM₁₀) and toxic metals observed in the city of Jaipur, India. A feed-forward network with a back-propagation learning algorithm is used to train the neural network the behavior of the data patterns. The meteorological variables of wind speed, wind direction, relative humidity, temperature, and time are taken as input to the network. The results indicate that the network is able to predict concentrations of PM₁₀ and toxic metals quite accurately.     

Evaluation of the Sodium Arsenite Method for Measurement of NO2 in Ambient Air

The sodium arsenite method for measurement of nitrogen dioxide in ambient air was evaluated. The method has a constant-high collection efficiency (82%) for nitrogen dioxide, and is insensitive to normal variations in operating parameters. Nitric oxide and carbon dioxide are positive and negative interferents, respectively. The combined average effect of these interferents, over ambient levels, is a positive bias of 9.9 µg/m³. This bias, although statistically significant, is minor ( 10 % ) in relation to the ambient air standard of 100 µg NO₂/m³ and does not warrant modification of the method to remove the interference.     

Control of Odors and Aerosols from Spent Grain Dryers

The information contained in this paper is directed to research workers concerned with odor identification and the development of methods for removal of odorous components from hot, moist stack gases and to application engineers faced with the practical problem of selecting effective, yet economical, odor control equipment for industrial operations. The new techniques described here demonstrate the beneficial uses of gas phase reactions as a conditioning step preceding absorption in a chemically reactive solution. Cost comparisons show markedly lower costs for full-scale reactor-absorbers than for gas incinerators for equal contaminant removal. Other methods of removing odors at the source, e.g., injection of ozone, use of nonvolatile oxidizing agents in solution, and adsorption on activated charcoal, were found to be impractical, ineffective, or both. The application of reactor-absorbers to spent grain drying is discussed in detail and reference is made to the use of this technique for other food industry waste treatment processes including rendering and fish and poultry meal production.     

Soil Bed System for Control of Rendering Plant Odors

Biofilter technology has been applied recently to treating rendering odors. Soil beds are one class of biofilter but as yet have not been used for this application. Although wet scrubbers have been a traditional method of odor control, their capital and operating costs are impacting more severely. Soil bed systems are less expensive to install and operate.

A soil bed system was installed at a rendering plant in Arizona and has been in operation since September 1983. The soil bed treats 1100 m³/h (650 cfm) of cooker noncondensables with a surface area of 420 m²(4500 ft²). The pressure drop across the soil bed is 5 cm (2 in.) of water. Odor sensory testing with the MTRI forced-choice triangle dynamic olfactometer indicates an odor removal efficiency of 99.9 percent is obtained with the soil bed. Soil bed odor removal efficiency is equivalent to or superior than that for incineration or scrubbing of high intensity odors from the rendering process. Recent experience during this past winter indicates a soil bed is a viable method for operation in a northern climate with severe winter weather conditions. Also, monitoring of the leachate from a soil bed indicated no contamination.     

Review of Federally Sponsored Research on Diesel Exhaust Odors

The information presented in this paper is directed to persons concerned with control of exhaust odors from diesel-engine-powered vehicles. This paper summarizes projects sponsored by the Environmental Protection Agency (EPA) over the past years in the field of diesel-exhaust odor. These investigations have concentrated on developing measurement methods for quantifying different odor levels, evaluating various odor control methods, and evaluating public opinions of such odors.

A human panel method using odor reference standards has been found suitable to measure these odor levels. In addition to this technique, chemical characterization work has been sponsored under a project jointly sponsored by the Coordinating Research Council and the EPA to isolate and identify those species responsible for the odor.

Knowledge of these odorous compounds and the techniques necessary to isolate them should lead to development of a chemical method to measure this type of odor, in place of human panelists. Such basic information would also lead to developing control techniques to minimize this odor.

Several control techniques were evaluated for diesel exhaust odor. To date, the most effective method is an improved needle injector for use in the Detroit Diesel type E 6V-71 engine commonly used in buses.

Finally, public reaction to diesel-engine-exhaust odor has been measured. It has been found that a systematic relationship exists between increasing public objections and increasing diesel odor intensity.     

Control of Odors from a Continuous Soap Making Process

Innovations in the use of lung and myocardial tissue in vitro have permitted continuous morphological observation of cells treated with a controlled gaseous environment. The mammalian tissues are covered with a dialysis membrane and cultured in a Rose chamber containing a large gas phase. Test gases can be flushed continuously through two hypodermic needles in the culture chamber wall. Cell movement and morphology have been recorded with time lapse cinematography in chambers containing cells washed from lung airways or organotypic lung cultures. Myocardial cell morphology and beating rate have been analyzed with the aid of a remote TV monitoring system. Histochemical and ultrastructural techniques were also applied. The beating rate of myocardial cells was found to be an objective and convenient endpoint for testing the characteristics of the exposure system. A comparison of the response of cells in the gas phase with that of elements in the fluid phase within the same chamber suggested that this system can serve as a model for evaluating the effect of an increasing diffusion barrier.     

Analysis of VOCs in Ambient Air Using Multisorbent Packings for VOC Accumulation and Sample Drying

Abstract

Solid multisorbent packings have been characterized for trapping and release efficiency of trace (10-20 ppbv in humidified zero air) volatile organic compounds (VOCs). The use of a two-stage trapping system reduces sample water content typically by more than 95.5% while maintaining a trapping and release efficiency of 100% for 49 VOCs, including eight water-soluble VOCs. Three combinations of primary tube and focusing tube are examined in detail by using an atomic emission detector to monitor hydrogen as an indication of residual water vapor, and to monitor either chlorine, bromine, or carbon for target VOCs. Linearity of response to individual VOCs, the presence of artifacts, and a laboratory monitoring application are also discussed.     

A Method of Predicting Point and Path- Averaged Ambient Air VOC Concentrations,Using Meteorological Data

A method of predicting point and path-averaged ambient air VOC concentrations is described. This method was developed for the case of a plume generated from a single point source, and is based on the relationship between wind directional frequency and concentration. One-minute means of wind direction and wind speed were used as inputs to a Gaussian dispersion model to develop this relationship.

Both FTIR spectrometry and a whole-air sampling method were used to monitor VOC plumes during simulated field tests. One test set was also conducted using only whole-air samplers deployed in a closely-spaced network, thus providing an evaluation of the prediction technique free of any bias that might exist between the two analytical methods.

Correlations between observed point concentrations and wind directional frequencies were significant at the 0.05 level in most cases. Predicted path-integrated concentrations, based on observed point concentrations and meteorological data, were strongly correlated with observed values. Predicted point concentrations, based on observed path-integrated concentrations and meteorological data, accurately reflected the location and magnitude of the highest concentrations from each test, as well as the shape of the concentration-versus-crosswind distance curve.