Dynamic Olfactometry Research Articles

Stages of Development of an Electronic Nose: Correlation Results Using a Dynamic Dilution Olfactometer in Conjunction with Human Experts

The different measurement techniques employed for gas and odor assessments are usually expensive, complex and time-consuming. Moreover, using these tools individually does not provide exhaustive information about odors under analyses. Therefore, this paper presents the development of a simple and low-cost odorant data logger as the second stage of the development of an electronic nose, combined with a classical technique as dynamic threshold olfactometry. The odorant data logger allows the estimation of odor concentration and odor intensity ratio of 1-butanol vapors, and it able to measure ethanol vapors. This instrument mainly comprises two commercial MOS sensors and an ATMEGA32 microcontroller. The odorant data logger showed an appropriate response to analytes' concentrations in parts per billion, detecting lower levels than reported by the sensors' manufacturer. Calibration curves were successfully adjusted to power-law functions, and the determination coefficients, R 2 , ranged from 93 to 99 %. An olfactometric analysis for 1-butanol vapors was performed, showing a suitable R 2 of 95.8 %. In order to estimate the odor concentration with the odorant data logger, a correlation with olfactometric values was also obtained. The values of R 2 were 97.9 % and 99.4 % for the TGS 2600 and TGS 2620 sensors, respectively. In addition, the odor intensity ratio was computed, as other estimated dimension of the odor. The results of this stage of the development are promising in terms of its future usage for several applications, which will be depending mainly on the sensors array and the processing tools.

Analysis of the possibility of using the modified INIG – PIB odorimetry snap prototype, for measurements by dynamic olfactometry method

Analysis of the possibility of using the modified INIG – PIB odorimetry snap prototype, for measurements by dynamic olfactometry method

Odour impact assessment of a large municipal solid waste landfill under different working phases

<p>Odours are among the main causes of complaints in regards to environmental issues for a variety of plants, including landfills. The emissions from landfills can affect the quality of life and negatively influence the area nearby. To protect people living in the surroundings from excessive odour exposures, different environmental protection practices may be implemented. In order to optimize technical and economic aspects, various configurations should be taken into account. In this view, the odour dispersion modelling represents a suitable tool to simulate different scenarios. In the present study, the odour impact from a large landfill located in Borgo Montello (Lazio Region, Italy) has been assessed by a dispersion model. Different operating conditions were simulated, in view of minimizing the odour annoyance during the phase of temporary closure of an area of the investigated plant. The Calpuff model was selected as it is well recognized among the preferred models for assessing the long range transport of pollutants. The Odour Emission Rates, inputs to the model, were calculated based on the results of dynamic olfactometry. The outputs from the dispersion model were investigated to define the best measures for the control of the odour emissions during the most impactful operations.</p>

On Line Monitoring of Odour Nuisance at a Sanitary Landfill for Non-Hazardous Waste

A field study was carried out to assess the possibility of monitoring online malodours from a sanitary landfill for non-hazardous waste. To that aim, the performance of a multisensory electronic nose and a H2S continuous analyser used in situ was evaluated to identify odorous compounds in ambient air emitted from the landfill as perceived at the nearest municipal receptor (the city of Statte, Southern Italy) and compared with the results obtained in laboratory by dynamic olfactometry. Alert situations were conventionally established when two consecutive H2S concentration measurements at 5 min intervals exceeded 20 ppb or when odour emissions measured by the e-nose exceeded 500 OU/m3 for more than 5 min. The study comprised two main activities: 1) training the e-nose to recognize the odorous compounds emitted from the landfill; 2) evaluating the efficiency of the H2S continuous analyser to provide useful information related to biogas emission. Activity 1 demonstrated the e-nose effectiveness for on-line monitoring, quantifying and identifying the odours produced by the landfill. Data processing showed that CDA was the most suitable algorithm to achieve best odours’ pattern recognition. Activity 2 showed that H2S measurements, depending on site-specific factors identified by Kolmogorov-Smirnov test, were poorly correlated with odour concentration in ambient air measured by dynamic olfactometry, as dynamic olfactometry takes into account the effect of other emitted compounds or the masking/enhancing effect of other compounds over H2S. Accordingly, further site-specific investigation is deemed necessary in order to achieve full on-line control of air quality and to adopt proper management measures at sanitary landfills and other odour emitting sources.

A Critical Evaluation of the Influence of Different Panel Composition in the Measurement of Odour Concentration by Dynamic Olfactometry

Odour concentration expressed in terms of OUE/m3 by using the dynamic olfactometry analysis, standardized by the European Norm (EN) 13725 are by now the most commonly and worldwide accepted method to measure odours. The EN, first edition published in the year 2003, is actually under review process by the WG2 of the CEN/TC246 and the end of the revision work is expected for the year 2018. Related to the odour panel the standard fixes some parameters (e.g: panel size). Nothing is, however, performed about the composition of the panel members in terms of their gender, the age of the involved persons and their origin and nationality. Also the current literature is limited to discussing how the measurement of emission rates derived from the same odour source could be related to the panel composition.The scope of this study is to investigate the influence on the determination of odour concentration with dynamic olfactometry, according to EN 13725 standards, applying different panel conditions, with the objective to define the optimal criteria to evaluate the odour concentration and obtain the highest repeatability and accuracy of the sensorial measure.A critical evaluation was carried out in relation to the same odour source with the comparison of the different panel composition (in terms of gender, age and nationality) to measure the odour concentration. In the experimental studies the measurements were conducted within 5 h after sampling to reduce the variability of the mixture and increase the reliability. All assessors who participate in odour measurements were qualified and tested according the quality criteria assurance foreseen by the EN13725. Studies were taken considering real environmental odour emissions collected at a wastewater treatment plant (WWTP).The results obtained show a not significantly influence of the investigated characteristics of the single panel member in the repeatability assurance of the measure of the odour concentration by dynamic olfactometry. While a variation of the results in terms of OU/m3 is demonstrated related to the different nationality and biological factors (age and gender) of the assessors. There is therefore the need to consider these factors in the current odour determination practices, for example in calculating the uncertainty factor of the measurement.

Full-scale composting of sewage sludge and market waste: Stability monitoring and odor dispersion modeling

The aim of this study was to assess the odor immission derived from full-scale composting of different abundant and highly pollutant organic waste: sewage sludge with bulking agent (SL), sewage sludge pretreated through anaerobic digestion and supplemented with bulking agent (SL-AD), and market waste with olive leaves (MW-OL). The combination of dynamic olfactometry and Gaussian dispersion modeling allowed both the quantification of odor emissions from each waste and the evaluation of their global odorous impact in nearby urban areas. Wind speed, summer and winter seasons, and atmospheric conditions were considered in the dispersion model. The results revealed that high wind speed (2.6 m/s) increases the global odor immission in summer season, independently of atmospheric stability. However, the maximum odor immission concentration recommended for composting process was not exceeded in any case, which depends on each country/region. The experimental results also enable to evaluate the influence of several physico-chemical variables on odor emissions derived from composting. The removal of nitrogen and volatile solids was the main cause for odor generation. Moreover, the microbiological activity of each substrate was monitored throughout the process and different percentages of biodegradability were quantified depending on the type of substrate and pretreatment applied.

Evaluation of the odor impact of some environmental gaseous pollutants: calibration of the methodology and preliminary results.

During the last decades, it has been observed a growing interest on odor impact because of the frequenter social acceptability problems about energy plants handling and processing stored organic materials (e.g., biogas plants, landfills, farms, distilleries, etc.). In this context, the UNI EN 13725:2004 indicates the "dynamic olfactometry method" as validated, recognized, and adequate measurement procedure for estimating the odor concentration. This protocol is carried out by a panel of specifically trained and selected human receptors, but alternative analytical methodologies are currently under discussion. This work aims to describe the initial steps of a wider research toward the definition of a new analytical protocol for monitoring odor concentration. The alternative methodology is here presented through the implementation of a case study: stored organic materials exploited on an energy plant in Central Italy. The paper describes the preliminary activities related to the survey of the case study (i), the definition of alternative methods and devices for conducting emissions sampling (ii), and the adopted experimental approach (iii). Finally, preliminary results are also presented (iv). The resulting protocol, once validated, could be employed by local authorities to measure both the odor impacts and the effectiveness of specifically designed mitigation strategies.

Scents in the stack: olfactometric proficiency testing with an emission simulation apparatus

Olfactometry is globally acknowledged as a technique to determine odor concentrations, which are used to characterize odors for regulatory purposes, e.g., to protect the general public against harmful effects of air pollution. Although the determination procedure for odor concentrations is standardized in some countries, continued research is required to understand uncertainties of odor monitoring and prediction. In this respect, the present paper strives to provide answers of paramount importance in olfactometry. To do so, a wealth of measurement data originating from six large-scale olfactometric stack emission proficiency tests conducted from 2015 to 2017 was retrospectively analyzed. The tests were hosted at a unique emission simulation apparatus—a replica of an industry chimney with 23 m in height—so that for the first time, conventional proficiency testing (no sampling) with real measurements (no reference concentrations) was combined. Surprisingly, highly variable recovery rates of the odorants were observed—no matter, which of the very different odorants was analyzed. Extended measurement uncertainties with roughly 30–300% up to 20–520% around a single olfactometric measurement value were calculated, which are way beyond the 95% confidence interval given by the widely used standard EN 13725 (45–220%) for assessment and control of odor emissions. Also, no evidence has been found that mixtures of odorants could be determined more precisely than single-component odorants. This is an important argument in the intensely discussed topic, whether n-butanol as current reference substance in olfactometry should be replaced by multi-component odorants. However, based on our data, resorting to an alternative reference substance will not solve the inherent problem of high uncertainty levels in dynamic olfactometry. Finally, robust statistics allowed to calculate reliable odor thresholds, which are an important prerequisite to convert mass concentrations to odor concentrations and vice versa.

Odour assessment in the vicinity of a pig-fatting farm using field inspections (EN 16841-1) and dispersion modelling

The assessment of odour annoyance varies vastly among countries even within the European Union. Using so-called odour-hour frequencies offers the distinct possibility for either applying dispersion models or field inspections, both generally assumed to be equivalent. In this study, odour-hours based on field inspections according to the European standard EN 16841-1 (2017) in the vicinity of a pig-fattening farm have been compared with modelled ones using the Lagrangian particle model GRAL, which uses odour-concentration variances for computing odour hours as recently proposed by Oettl and Ferrero (2017). Using a threshold of 1 ou m−3 (ou = odour units) for triggering odour hours in the model, as prescribed by the German guideline for odour assessment, led to reasonable agreements between the two different methodologies. It is pointed out that the individual odour sensitivity of qualified panel members, who carry out field inspections, is of crucial importance for selecting a proper odour-hour model. Statistical analysis of a large number of data stemming from dynamic olfactometry (EN 13725, 2003), that cover a wide range of odorants, suggests that the prescribed method in Germany for modelling odour hours may likely result in an overestimation, and hence, equivalence with field inspections is not given. The dataset is freely available on request.

Difficulties of olfactometric evaluation in patients accusing smell disorders after head trauma

Abstract Head trauma is considered to be the third cause of olfactory function disorders. Olfactometric assessment in patients accusing anosmia following head injury produced by car accident or aggression is important, because most of them are involved in law trials in order to obtain financial compensations from the author. It is compulsory to use both subjective and objective olfactory evaluation methods combined with a detailed anamnesis, a complete ENT examination and a good cranio-facial imaging (computed tomography or MRI) in order to exclude malingerers and to obtain an accurate diagnosis. “Sfanta Maria” ENT Department from Bucharest is the only center in Romania where the olfactory function in completely investigated. We use chemosensory (Snap and Sniff Test and n-Butanol Dynamic Olfactometry) and electrophysiological tests (electric olfactory evoked potentials of the olfactory bulb). Unfortunately, we confront with a series of difficulties in what concerns the smell function evaluation: 1) there is scarce information in the literature regarding the olfactory electric evoked potentials; 2) the electric olfactory evoked potentials register only the electrical activity in the olfactory bulb; 3) in case of olfactory impairment medically confirmed, we cannot establish a cause-effect relationship between the disturbance and the event; 4) the most accurate electrophysiological assessment method currently available in Europe is the time-frequency analysis of chemosensory event-related potentials, but we do not dispose of the necessary equipment yet; 5) sometimes patients do not give us the informed consent for a complete olfactory evaluation.

Technology for Intensive Poultry Production as a Source of Odour Emissions with Time-Varying Intensity

Abstract The technology for intensive broiler breeding using deep litter method provides convenient conditions for production of odour substances inside the barn. As a consequence, there are relatively high odour emissions in the breeding area and its surrounding, which has significant impacts on the life quality of both people and animals. The amount of produced emissions increases in time because it is closely related to the amount of poultry droppings accumulated in litter inside the barn. This paper deals with changes in odour intensity depending on time measured since the beginning of broiler fattening. Odour intensity was measured by methods of dynamic olfactometry. The estimated values gradually increased from 45 ouE·m-3 to the highest value of 259 ouE·m-3, which was determined in the final fattening phase (broilers’ age 33 days). The calculated odour substances emission values were in range from 0.02 ouE·s-1·bird-1 at the beginning of fattening up to 0.10 ouE·s-1·bird-1 in the final fattening phase. Odour emissions increased five times during the fattening period.

Anaerobic digestion coupled with digestate injection reduced odour emissions from soil during manure distribution

This work aimed to measure the odour impact of untreated cow and pig slurries and treated (digestate and liquid fraction of digestate) manures when they were used on soil at a field scale, while also testing different spreading methods, i.e. surface vs. injection. Five experiments were performed in 2012–2016 on different farms. Odours were quantitatively (specific odour emission rate – SOER) (OUEm−2h−1) measured by using dynamic olfactometry and qualitatively, i.e. to obtain an “odour fingerprint”, by using an electronic nose (EN).Anaerobic digestion was effective in allowing the reduction of potential odour emission from digestates, so that when they were dosed on soil, odours emitted were much lower than those from soils on which untreated slurries were used. Slurries/digestate injection reduced much more odour emitted by soils so that SOER tended to become more similar to that of the control (untreated soil) although the odours were slightly greater.Odour fingerprint data indicated that there was a direct correlation between SOER and odour fingerprints. This was due to the ability of EN to detect ammonia, S-compounds and methane that were (the first two mainly), also, responsible for odours. Very good regression was found for Log SOER and EN by using a Partial Least Square (PLS) approach (R2=0.73; R2cv=0.66; P<0.01) for matrices used to fertilize soils in lab tests. Unfortunately, regression was not so good when odour data from field experiments on soil were used, so that EN cannot be proposed to replace olfactometry. EN fingerprints for control (Blank) and injected organic matrices were virtually identical, due to the creation of cavities in the soil during the injection that decreased the treated surface. Anaerobic digestion and subsequent digestate injection allowed us to reduce odour impact, avoiding annoyance to local inhabitants.

Variations of odorous VOCs detected by different assessors via gas chromatography coupled with mass spectrometry and olfactory detection port (ODP) system.

Odorous volatile organic compounds (VOCs) were analysed via a thermal desorption gas chromatograph coupled with a mass spectrometer and olfactory detection port (TD-GC-MS/ODP) to characterize odour emissions from a wastewater treatment plant (WWTP). Three trained ODP assessors, screened according to the European dynamic olfactometry standard (EN: 13725), were used for the olfactory analysis. Their sensitivity to n-butanol varied within the acceptable limits. VOC samples from the WWTP were collected onto Tenax TA sorbent tubes in triplicate and each assessor analysed one tube in the same sample desorbing and analysing conditions. Intensities of odours detected from ODP were scaled from 1 to 4. The ODP assessors used their own odour descriptors based on their own experience as well as referenced descriptors on published compost and wastewater odour wheels. The ODP assessors detected a total of 32 different odorous VOCs; however, the intensities assigned by each assessor to particular VOCs varied. Moreover, some odorous VOCs were not detected by all assessors. For example, geosmin was detected by only two assessors. The use of a TD-GC-MS/ODP system for the analysis of odorous VOCs is valuable when analysed by different assessors, allowing a range of responses to specific odorants in a populations to be investigated.

Environmental Impact Assessment of Odours from Solid Waste Landfills Located in Highly Urbanized Areas

Urbanization and the rise in the standard of living generated both a higher quantity of waste and the expansion of cities with the incorporation of solid waste landfills located originally outside. In many cities across Romania, landfills are placed very close to settlements, and in some cases even inside cities. Beside landfill activities, other companies that deal with waste sorting, recycling and treatment operates nearby. All these activities generate odorous compounds that create odour nuisance. The current study was conducted in order to evaluate the impact of a landfill located in a highly urbanized area using dynamic olfactometry with the main objective to assess the level of odour concentration and the impact on the population. Samples were taken around the landfill always from a point opposite to the wind direction. Also, in parallel with odour sampling it was determined the concentration of two main chemical specific compounds, NH3 and H2S, in order to verify the compliance with environmental legislation, and the level of VOC to establish a correlation with the odour level. Measurement results indicate a high level of odour concentration in most of the samples, a good correlation with VOC and frequent exceeded values for the specific chemical compounds. Annoyance level was also high and it was evaluated using FIDOL factors, which are Frequency, Intensity, Duration, Offensiveness and Location.

Improving the repeatability of dynamic olfactometry according to EN 13725: A case study for pig odour

Dynamic olfactometry, according to the standard EN 13725:2003 (CEN, 2003), is the reference method in Europe to measure odour concentrations and emissions from agricultural and industrial facilities. Laboratory measures to improve the precision (repeatability) of olfactometry were investigated here, focussing on the reference odorant, n-butanol and on pig house odour as an environmental odour. The effects of panel size, of the panellists' performance level, of the odour type and of the number of rounds on the olfactometric precision were studied. A precision-analysis tool was developed in Matlab, which randomly constituted 20,250 odour panels and randomly selected odour thresholds to generate 40,500 odour concentrations, calculated according to EN 13725. These simulations were performed, using 10 datasets of in total 776 olfactometric thresholds, measured by CEN-qualified panellists. The first results (reference odorant only) indicated that the panellists' performance level, the panel size and the number of rounds all significantly affected the laboratory's repeatability and that increasing the panel size, improved the repeatability the most. In a second study, comparing n-butanol and pig odour, as well odour type, as panel size, as the number of rounds significantly influenced the laboratory's repeatability. Odour type had the highest influence, followed by an increasing panel size. Based on these two studies, increasing the panel size seems a good means for improving the repeatability. For pig odour specifically, increasing the number of rounds from 2 to 3, improved the repeatability as much as one extra panellist.

Comparison of different measurement methods of odour and odorants used in the odour impact assessment of wastewater treatment plants in Poland.

The aim of this study was to compare sensory and analytical methods used to measure odour and odorants concentrations for odour impact assessment on municipal wastewater treatment plants (WWTPs). A range of sources and odour or odorants concentrations were used to compare the methods. Four different odours and odorants measurement methods were compared: field olfactometry using Nasal Ranger® field olfactometer, dynamic olfactometry according to PN-EN 13725:2007 standard, colorimetric assays (hydrogen sulphide, ammonia) and gas chromatography-mass spectrometry (GC-MS) methods (methanethiol, ethanethiol, dimethyl sulphide). Mechanical-biological and mechanical-biological-chemical WWTPs were chosen. Receptor points were selected inside of 'closed' facilities of the technological line (screening rooms, mechanical thickening and dewatering building) and downwind at 'open' facilities (collection chambers, sand trap, mechanical thickeners) which were the most significant regarding the potential for odour nuisance. By the research, it is not possible to specify explicit dependencies between results obtained from different research methods used in the odour impact assessment of WWTPs. A strong correlation (Pearson's correlation coefficient was equal R = 0.79) was determined only once between odour concentrations measured by dynamic olfactometry and methanethiol concentrations in the screen room at the WWTP No. 3.

Dynamic olfactometry and sample toxicity. a case study for a MSW incinerator odour assessment project

The study reported in this paper is focused on occupational exposure to potential toxic compounds for employees working in dynamic olfactometry, following EN 13725:2003 standard procedures.Municipal solid waste (MSW) incineration plants, typically, have authorized stack emissions for primary pollutants (like CO, NOx, particulate), for selected trace organics (polycyclic aromatic hydrocarbons (PAHs) or dioxins), metals or for total organic compounds (TOC). Odour control is limited on recommendations of good practices for the waste receiving areas and storage, generally on the air management systems.In Italy there is an increasingly number of requests, to environmental inspection authorities, Agenzia Regionale per la Protezione Ambientale (ARPA), Regional Environment Agency, to quantitatively describe possible odour annoyance effects from different industrial plants, including MSW incineration plants. Recently ARPA Piemonte has been asked to perform one odour survey for the newly incinerator for the city of Torino, that burns 500,000 t/y of MSW recovering energy through cogeneration. The plant is equipped with a pollutant's automated measuring system (AMS) to assess the compliance with the emission limit values, but not to measure odour emissions. For this reason, it is necessary to assess odour emissions as well, in order to prepare an exhaustive environmental odour scenario for the whole area.We recently presented a risk assessment approach, to evaluate non-carcinogenic and carcinogenic compounds for different sample types, based on STEL or TWA data, or EPA slope factors values respectively. It has been decide to follow this approach to define potential sample toxicity (PT), using the different risk occupational scenarios proposed, before odour concentration analysis of stack emissions samples. Using emission limit values that are set in the permit, PT has been defined. Since samples are presented to assessors in an ascending concentration series, workers exposure has been limited to acceptable levels defining the specific minimum dilution value to be used in the ARPA Piemonte olfactometric laboratory standard procedures.

Proposal of Odor Nuisance Index as Urban Planning Tool.

This article analyzes the state of the art of the methods and models used for the characterization of odor annoyance and it preliminary advances some proposals for the evaluation of the olfactory nuisance. The use of a sensorial technique, such as dynamic olfactometry, is proposed for the analysis of odor concentrations, odor emission rates, and odor dispersions. A simple model for the quantification of environmental odor nuisance, based on the use of FIDOL factors, that are, frequency, intensity, duration, hedonic tone, and location, is proposed.

Odour measurement in wastewater treatment plant using both European and Japanese standardized methods: correlation and comparison study

&lt;p&gt;Odours discharged from wastewater treatment plants generally cause severe damage to locals. When facility odors affect air quality and cause citizen complaints, an investigation of those odours may require using standardized scientific methods. Odour intensity is one of the main odour characterization parameter, and represents an important sensory indicator of environmental odours.&lt;/p&gt; &lt;p&gt;Presently, different international standards have been developed for the measurement of odours. Main consolidated methods are the measurement of odour index assessed by panelists, standardized in Japan and developed there more than 40 years ago; and the measured of odour concentration by dynamic olfactometer according to European standard EN13725:2003.&lt;/p&gt; &lt;p&gt;In this study odour samples were collected on a municipal wastewater treatment plant to investigate the relationship between odour index assessed by Japanese standard methods and odour concentration measured with dynamic olfactometry. A monthly sampling and relative odour measurement were carried out for consecutive 8 months at the Laboratory of the Sanitary Environmental Engineering Division (SEED) at the University of Salerno (Italy).&lt;/p&gt; &lt;p&gt;Results show a strong linear correlation between the two investigated odour measurement methods, in the case of the measurement of high concentrations. While at lower odour concentrations were observed a difference between the two methods.&lt;/p&gt;

Characterization of odours emitted by liquid waste treatment plants (LWTPs)

&lt;p&gt;Odour emissions from liquid waste treatment plants (LWTPs) generally cause significant effects on the environment in terms of nuisance to exposed population. The particular and complex nature of the mixture of the volatile substances, its variability in time and the strong influence of the atmospheric conditions, are the elements that delayed their regulation and relative management.&lt;/p&gt; &lt;p&gt;Limited data are available in the technical and scientific literature, regarding the odour emissions characterization from liquid waste treatment plants. Moreover there isn’t a common strategy from the different European Countries in the regulation of their emissions.&lt;/p&gt; &lt;p&gt;Different methods can be used to measure odour emissions from environmental engineering plants, and currently, in Europe, the most used techniques for odour emissions characterization and quantification is the dynamic olfactometry, according to EN 13725:2003.&lt;/p&gt; &lt;p&gt;The aim of this study is the characterization of the odour emissions from different liquid waste treatment plants (LWTPs), trough a case study of two large real LWTPs, in order to identify the principal odour sources and to define their related odour emissions.&lt;/p&gt; &lt;p&gt;Odour Concentration Index (OCI) is proposed as a useful and simply odour management tool for the identification of the priority actions necessary to identify and control the main odorous sources. Relationship between the measured odour emissions and the types of treated liquid waste (identified in terms of EWC code, COD and NH4&lt;sup&gt;+&lt;/sup&gt;) is also discussed.&lt;/p&gt; &lt;p&gt;Results show that the influent collection tank is the source with the highest detected odour emissions. OCI results are useful for the definition of a clear priority action for odour control, similar for both investigated plants. Between the characterized types of liquid waste treated by LWTPs the leachate (EWC 190703) show the maximum odour emissions.&lt;/p&gt;