An Odour Attribution Study is undertaken in North America for an Air Quality Management Agency that includes athering data from specific sources and ambient locations to better understand odour impacts within the local communities. Specifically, the following objectives were to be met:

  Identify odorant compounds impacting the area of concern via comprehensive quantitative and qualitative analyses; Determine the relative contribution and variability of the odorant compounds emitted from the three key source facilities; Develop a strategy for continuous real-time odorant monitoring to measure emissions impacting the community from the three key source facilities.

   Competing interests: The author has declared that no competing interests exist.

   Academic editor:  Carloz N. Díaz

   Content quality: This paper has been peer-reviewed by at least two reviewers. See scientific committee here

   Citation: Jay Witherspoon, Jerry Bovee, Scott Cowden, Mel Suffet, Bart Kraakman. 2021. An odour attribution study to determine the relative contribution from three facilities for the development of real-time odour monitoring, 9th IWA Odour& VOC/Air Emission Conference, Bilbao, Spain, Olores.org.

   Copyright:  2021 Olores.org. Open Content  Creative Commons license. It is allowed to download, reuse, reprint, modify, distribute, and / or copy articles in olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.

   ISBN: 978-84-09-37032-0

   Keyword: Odor Profile Method, field olfactometry, PTR-MS.

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Abstract

  An Odour Attribution Study is undertaken in North America for an Air Quality Management Agency that includes gathering data from specific sources and ambient locations to better understand odour impacts within the local communities. Specifically, the following objectives were to be met:

• Identify odorant compounds impacting the area of concern via comprehensive quantitative and qualitative analyses;
• Determine the relative contribution and variability of the odorant compounds emitted from the three key source facilities;
• Develop a strategy for continuous real-time odorant monitoring to measure emissions impacting the community from the three key source facilities.

   Odour has been an issue in this area for decades. Over the years, various odour mitigation approaches have been undertaken with varying degrees of success. While the number of odour complaints from residents has decreased in recent years from a peak of 3,500 in 2015, the high number of complaints (1,500) reported for 2018 indicates a persistent and ongoing odour issue. The odours in the area originate primarily from three closely located facilities including:

• A Waste Recycling Facility (including a waste recycling facility, a composting facility and a landfill)
• A Wastewater Treatment Facility
• An Anaerobic Organic Material Digestion Facility

   The study approach goes beyond using the traditional, common practice of using odour threshold or odour intensity as the measure of odour nuisance. Instead, Weber-Fechner (persistency) curves were used as part of the Odor Profile Method (OPM) developed by Dr. Mel Suffet of the University of California-Los Angeles. The usefulness of the OPM lies in the fact that the human nose is, for the most important odorants, many degrees more sensitive than the standard chemical compound identification analytical methodologies. The approach was combined with comprehensive chemical compound identification analyses, field olfactometry sampling and well as a proton-transfer reaction time-of-flight mass spectrometer (PTR-MS) to provide targeted measurements of specific VOCs to collect chemical fingerprints associated with the different sources. An improved understanding of the relative contribution of odour causing compounds from the three facilities and how they impact the local community was obtained to better:

1. inform future actions to reduce odours (best practices, enforcement, rules)
2. establish methods to measure progress on facilities' future odour reduction actions
3. educate community - on what's causing the odours, how complex they are and teach them how to characterize to better inform ongoing improvement efforts.

 1. Introduction

  The Bay Area Air Quality Management District (Air District or District) in California has undertaken an odour attribution study to identify compounds that may be impacting a local community from three closely located facilities with similar odour profiles.

   Odour has been an issue in this area for decades. Over the years, various odour mitigation approaches have been undertaken with varying degrees of success. While the number of odour complaints from residents has decreased in recent years from a peak of 3,500 in 2015, the high number of complaints (1,500) reported for 2018 indicates a persistent and ongoing odour issue. The odours in the area originate primarily from three closely located facilities including:

• Facility A: An Anaerobic Organic Material Digestion Facility;
• Facility B: A Waste Recycling Facility (waste recycling facility, composting facility, and a landfill);
• Facility C: A Wastewater Treatment Facility,
  while other natural sources were also considered (lift stations, bay, estuary).

   The goals of the project are to determine the contribution and variability of odour causing compounds from these facilities and develop a strategy for measuring how often and at what concentration these potential odour causing compounds may be passing into the local community.

   The first goal is to provide a means of quantifying specific odorous compounds and their co-relationships to other compounds (“odour fingerprints” or “odour signatures”) that occur from each facility. It needs to determine how unique to the facility the odour signature may be. It also aims to determine the diurnal and seasonal variation of specific compounds concentrations and have them correlated with nearby resident’s complaints of odour impacts.

   The second goal is to propose a method (or combination of methods) to employ so that ongoing measurements can be taken along the facility’s fence line, or other locations in the community. The method would indicate odour emissions from a given facility and at what proportions. This would help the stakeholders to:

1. Inform future actions to reduce odours - best practices, enforcement, rules
2. Establish methods to measure progress on facilities' future odour reduction actions
3. Educate community - teach the community how to characterize the different odours to understand better where they are coming from and how they impact the community (make optimal use of the community in ongoing effort to reduce odour impacts)

2. Methodology

   The study approach goes beyond using the traditional, common practice of using odour threshold or odour intensity as the measure of odour nuisance. This study also includes the development of Weber-Fechner (persistency) curves as part of the Odor Profile Method (OPM) developed by the group of Dr. Mel Suffet of the University of California-Los Angeles (Burlingame, 1999 and 2009). The usefulness of the OPM lies in the fact that (1) the human nose is, for the most important odorants, many degrees more sensitive than the standard chemical compound identification analytical methodologies and (2) that the persistency of odorous compounds can differ from each other and therefore quantifying the odour intensity reduction with dilution and characterizing the dominate type of odours can help with understanding what type of odorous compounds are most critical when developing odour control strategies.

   The approach was combined with comprehensive chemical compound identification analyses, field odour characterization and field olfactometry surveys and well as a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) to provide targeted measurements of VOCs to develop ‘chemical fingerprints’ of the odours associated with the different sources.

   Two large sampling events were undertaken in late October 2020 and mid May 2021 that involved several teams to take samples and measurements. All sample collected in bags were analyzed the same or the next day. The summary of the sample collection and sample analysis methods are summarized Table 1. Weather data was collected during the sampling events using a mobile weather station augmented by data from a local weather station at one of the facilities and weather data from the nearby airport.

Table 1: Summary of the odour sample collection and analysis methods used.

   In addition to the two sampling events field assessments using field olfactometers have been undertaken by the nearby city council staff every two or three weeks during an 18-month period from early winter 2019 till the summer of 2021. In total about forty field assessment were performed by two staff members each time at ten discrete locations in the community. The locations were selected based on their history of relatively large amount of odour complaints. Beside odour strength measured by the field olfactometer, also odour character, odour intensity and hedonic tone were determine using an ‘odour wheel’ and pre-defined scales for odour intensity and hedonic tone. A mobile weather station was used to determine wind speed and direction at the discrete location at the time of the field assessments.

3. Result and discussion

   Table 2 summarizes the key odour sources at each facility and the odour characterization results of in-field olfactometric assessments performed over a period of 18 months.

Table 2: Summary of the key odour sources at each facility.

1) Odour Intensity scale as measured just outside the fence-line: Not Detectable (0), Very Weak (1), Weak (2), Distinct (3), Strong (4), Very Strong (5), Extremely Strong (6) 2) Hedonic Tone scale as measured just outside the fence-line: Pleasant (1), Neutral (0), unpleasant (-1), revolting (-2), nauseating (-3)

   Odour Activity Values (OAVs) quantify odour potency/importance and is defined as the ratio of measured mass concentration of an odorant to its odour threshold concentration (OTC). Figure 1 below provides a comparison of OAVs for the key measured odour sources at the three facilities. Any OAV that exceeds 10 is considered to be a possible nuisance odour as it represents an odorant that requires a minimum atmospheric dilution of 10:1 to reduce the strength of the odorant to below its OTC. Therefore, the OAV action level is equal to 10 and is showed as dashed red line below.

• Sulfur-compounds (characterized as rotten eggs, rotting vegetables) are shown as blue;
• Aldehydes (characterized as sweet) are shown as red;
• Carboxylic Acids (characterized as rancid) are shown as yellow;
• VOCs (characterization varies) are shown as green;
• Amine (characterized as fishy) are shown as brown.

Figure 1: Odour Activity Values (OAVs) and the odour potency/importance in terms of the ratio of measured concentration of an odorant to its odour threshold concentration.

   Examples of the Odor Profile Method (OPM) results are shown in Figure 2 and illustrate the odour intensity reduction with dilution (persistency curves) as well as the character of the dominate type of odours at each dilution. This illustrates how odour intensity and odour
character changes when it travels from the different odour sources into the community. The results showed that air coming from the facilities can pose odour nuisance with a unique character for the community near each facility and possibly a weak odour nuisance for the area further away from each facility that may have changed in odour character. Certain masked odours persist and travel further into the community while the original character of the odours dissipate with dilution.

Figure 2: Examples of odour persistency curves (odour intensity vs dilution) of the odours emitted from different odour sources as determines with the Odor Profile Method (OPM): Internal Space of Facility A (left),

   The field surveys using field olfactometers were undertaken on a regular basis over a period of 18 months. Figure 3 shows an initial BLOB map of the likely odour impacts in the community and the contributions to the odour intensity from each facility based on the odour character descriptions during the in-field odour olfactometric assessments.

   In addition, PTR-TOF-MS have provided ‘chemical fingerprints’ and have shown a measurable difference in chemical composition of the odours from the key odour sources. This confirms the results that were obtained using the in-field olfactometric analyses, the OPM analyses and the lab chemical analyses as well as the lab olfactometric analyses (data not shown) that the odour signature is unique to each facility.

4. Conclusions and next steps

   An improved understanding of the relative contribution of odour causing compounds from three closely located facilities is obtained and how they impact the local community.

   The next steps are to improve the understand of seasonal variation of these odour contributions and to develop and propose a method (or combination of methods) to employ so that ongoing monitoring. This ongoing monitoring will be implemented along the facility’s fence line, or other locations in the community to help the stakeholders inform on future actions to reduce odours.

Figure 3: A BLOB map with odour impacts in the community and their contributions to the odour intensity from each facility based on initial in-field odour olfactometric assessments.

   Acknowledgement: Funding provided by the Bay Area Air Quality Management District (BAAQMD) and the City of Milpitas. The authors like to acknowledge the many stakeholders, including staff from the different waste recycling/resource recovering facilities, BAAQMD staff and City of Milpitas staff for their outstanding contributions.

References:

   EN 13725. Air Quality - Determination of Odour Concentration by Dynamic Olfactometry. European Committee for Standardization (CEN).

   Burlingame, G.A. Odor Profiling of Environmental Odors. Water. Sci. Tech. 1999, 40, 31–38.

   Burlingame, G.A. A Practical Framework Using Odor Survey Data to Prioritize Nuisance Odors. Water Sci. Techl. 2009, 59, 595–602.

   EPA (1999) EPA/625/R-96/010b Compendium Method TO-17: Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling onto Sorbent Tubes.