Exploring Natural Models for the ‘Rolling Unmasking Effect’ of Downwind Odor Dispersion; Prairie Verbena, Prehensile-Tailed Porcupine and Virginia Pepperweed

As natural scale-models for community environmental odor issues, these odorant prioritization results illustrate an important consideration: ... ‘with respect to focusing an environmental odor issue, it is possible to look too closely at the source’... Although simple odor dilution, as measured by odor concentration and intensity, certainly occurs during downwind dispersive migration from the source, these authors propose that the term dynamic dilution is limiting with respect to environmental odor impact. The results presented herein suggest that the odor character from an environmental source can vary dramatically, depending upon the distance of the human receptors from that source. It is further suggested that the process of downwind environmental odorant prioritization can best be characterized as a rolling unmasking effect or RUE. The RUE is exhibited by the masking odors nearest the source sequentially ‘falling away’ with distance from the source, revealing a succession of increasingly simplified odor characteristic and composition. Because of scaling factors and meteorological unpredictability, the logistics involved in carrying-out odorant prioritization studies can be very challenging when targeting large-scale odor sources. However, for these authors’ illustrative purposes, these challenges were reduced significantly by selecting natural, ‘scale-model’ odor-sources which represented significant reductions in the primary scaling factors; especially, reductions in the size of the odor sources and the distance of their downwind reach. Driven by odorant prioritization and the RUE, extremes of odor simplification-upon-dilution were demonstrated for two Central Texas plant varieties, prairie verbena and virginia pepperweed. Their ‘odor frontal boundaries’ were shown to be dominated by single, characterdefining odorants; prairie verbena presenting with a p-cresol dominated ‘barnyard’ odor and virginia pepperweed with a benzyl mercaptan dominated ‘burnt match’ odor. Similar odor simplification was also shown for the South American prehensile-tailed porcupine (i.e., pt porcupine); its downwind ‘odor frontal boundary’ dominated by two potent, character-defining odorants (i.e. as yet unidentified): (1) ‘onion’/‘body odor’ odorant #1 and (2) ‘onion’/‘grilled’ odorant #2. In contrast to their outer-boundary simplicities, each of these sources also presented, at the source, with odor compositions reflecting considerable complexity and corrresponding composite odor characters that were distinctly different from those reflected at their respective ‘odor frontal boundaries’.

presented herein suggest that the odor character from an environmental source can vary 23 dramatically, depending upon the distance of the human receptors from that source. It is 24 further suggested that the process of downwind environmental odorant prioritization can 25 best be characterized as a rolling unmasking effect or RUE. The RUE is exhibited by 26 the masking odors nearest the source sequentially 'falling away' with distance from the Although relatively intuitive and demonstrable, odorant prioritization does not appear to 53 be widely recognized or referenced within the environmental odor field. With respect to 54 contemporary environmental odor issues, it is still common to see an odor issue 55 presented, roughly correlated to an extensive inventory listing of volatile chemicals 56 which are shown to be emitting from a 'suspect' odor source. For example, one study, 57 focused directly on odor emissions from sewage treatment facilities ( 66 downwind odor impact beyond the source fence-line. It is also often the case that these 67 extensive inventory VOC listings fail to actually include the specific VOC odorant, or 68 odorants, which are primarily responsible for the targeted at-distance odor. In one 69 notable example from an odorant prioritization study to the rendering industry (Caraway 70 et al; 2007), two odorants, trimethylamine and dimethylsulfide were identified as the 71 impact-priority odorants downwind of a fish meal processing plant; a rendering facility 72 specializing in the processing of fish and fish by-products. This finding stands in marked 73 contrast to an earlier study (Luo et al, 1997), reporting ~300 organic compounds, 40 of 74 which were odorous and stating that 'odorous compounds included alkanes, alkenes, 75 ketones, hydrocarbons, alcohols, alkyl halides, fatty acids, amines, aromatics, aldehydes 76 and epoxides'. It should be pointed out that this 300 compound listing did include 77 trimethylamine and dimethylsulfide but those were not prioritized within this 300 78 compound inventory listing. Although simple odor dilution, as measured by odor concentration and intensity, certainly 108 occurs during downwind dispersive migration from the source, this term is limiting with 109 respect to environmental odor impact  In recent years, it has been proposed that the process of environmental odorant 116 prioritization can better be described as a RUE (Figure 1) With regard to MDGC heart-cut isolation / clean-up of the 2 target 'onion' odorants for 209 the pt porcupine; (1) optimal band for heart-cut #1 (i.e. unknown 'onion' odorant #1) 210 was approximately 9.9 to 11.2 min; (2) optimal band for cryotrap #1 was approximately 211 9.4 to 11.5 min; (3) optimal band for heart-cut #2 (i.e. unknown 'onion' odorant #2) 212 was approximately 14.4 to 15.8 min; (4) optimal band for cryotrap #2 was approximately 213 13.9 to 16.1 min; (5) long SPME collection of the whole urine headspace yielded 214 overwhelming odor responses but NO obvious associated mass spectral ion detail for the 215 critical 'onion' odorants. In contrast to the MDGC based heart-cut, isolation protocol, as Environmental air sample collections from pt porcupine exhibit: SPME fiber direct 234 exposure: A series of direct environmental air samples were collected and analyzed in 235 conjunction with this current effort, utilizing a direct SPME fiber exposure approach. 236 The SPME fibers which were prepared for this segment of the project were: (1) segment of the investigation. Preconditioned SPME samplers were secured onto a field-243 support fixture within the exhibit enclosure; the adsorbent coated fiber tips extended from 244 their protective needle sheaths (i.e. exposed to the enclosure environment to effect VOC 245 collection through surface adsorption). Volatiles loadings on the SPME fibers were 246 varied by altering the length of time the SPME fibers were exposed to the air 247 environments. Fiber exposures reflecting brief sampling intervals were executed for 7 248 and 9 minutes, respectively. Duplicate SPME fiber exposure intervals reflecting long 249 exposure intervals were exposed for 15 hours. The 4 direct fiber collections were return  based on best-match ranking of the experimental spectra against these databases.

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The samples of pt porcupine urine and virginia pepperweed (same batch of materials that 343 was used by first author) were analyzed by this investigator in order to further explore 344 identification of some leading odor notes. The headspace volatiles collection was 345 conducted in a manner described above for the first author. The spectral data was 346 reviewed in detail but, despite best efforts, failed to identify the two targeted 'onion'  Through analytical testing of the guiding premise, the authors demonstrate the odorant 456 prioritization process through a 'cradle-to-grave' odor profile assessment of the regional  The approximate odorant priority subset for the prairie verbena can be summarized as:

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(1) p-cresol (character-defining 'barnyard' or 'hog-truck' at the odor frontal Secondary priority impact was assigned to an odorant, eluting @ 6.0 min, which carries a 645 distinct 'ether' or 'ketone' odor. Initial mass spectral fragmentation pattern data suggests 646 that this unknown could be a series of -oxime isomers but this prospect remains 647 speculative, at this juncture. Key supporting evidence for the secondary priority ranking

Ketones
Ketones acetone 2-octanone 2-butanone 6-methyl-5-heptene-2-one 2-undecanone pentadecanone diacetyl 1-octene-3-one 1-octene-3-one Esters cis-carvyl acetate This was so much the case that upon first encounter with the odor frontal boundary, the 741 first author actually began looking upwind of that location, trying to determine where the 742 food court must be located; certain that that must be the source. The odor was 743 surprisingly strong and reminiscent of 'grilled onion' or, as described by the first author 744 at the time, '50s hamburger joint'. However, upon walking a bit deeper into the odor 745 plume, there was encountered, almost simultaneously, an intense foul odor and an 746 associated permanent exhibit display sign which read; 'What is that Foul Odor?'. The confirmed that, accompanying the predicted '50s hamburger joint' odor note (i.e. 774 unknown 'grilled onion' @20.8 min RT), was a second, earlier eluting 'onion' note (i.e. 775 unknown 'body odor onion' @13.9 min RT) with a similar odor character. Remarkably, 776 beyond these two character-defining odor notes, the extremely complex headspace odor 777 profile appeared to be free of other members from the onion-sourced allylic-polysulfide 778 family. As shown in Figure 9 and 10 below, these two character-defining 'onion' 779 odorants were shown to emerge from an extremely large and complex odorous VOC 780 field; a compositional field previously shown to be common to mammalian waste in isolation / clean-up from SPME headspace volatiles collection (Figure 11, 12 and 13 character (Boelens, et.al., 1993;McGorrin. 2007; May- Chien Kuo, et.al. 1990). Work

Miscellaneous
Miscellaneous 2-methyl furan 2-methyl furan 2-methyl furan 1,3-pentadiene 2-pentyl furan dimethyl pyrazine dimethyl pyrazine 4,8-dimethyl-1,3,7-nonatriene acetamide 1-methoxy-1,3,5-cycloheptatriene 4-methyl pyridine tridecane propanamide 6-heptyltetrahydro-2H-pyran-2-one butanamide 3 -m e t h y l -phenyl acetate phenyl ethyl alcohol pentamide 2 -pyrrolidinone hexadecane valerolactam 5 -m e t h y l -2 , 4imidazolidinedione Notes: * -many chemical identifications, beyond the impact-priority compounds, should be considered as 839 tentative; they are the product of best-match efforts from Wiley and NIST mass spectral libraries matching. interesting contrast to the VOC compositional profile of the North Texas commercial 847 swine barn. This is clearly reflected in comparing the Table 1 and traceable, dominantly or exclusively, to benzyl mercaptan. As shown below in Figure   relative to the source. In the illustrative cases presented herein these subsets are, 950 respectively, (1) the benzyl mercaptan driven 'burnt match' odor of virginia pepperweed; 951 (2) the two unknown 'onion' odorant driven 'grilled onion' odor of the pt porcupine and combined subset consists of the 5 to 7 odorants leading the comparative listing in Table  sample-prep mode, for on-the-fly purification / isolation / capture of 'suspect', high-1265 purity reference odorants from readily available crude source materials.