The Perceived Intensity of Natural Odors T. E. Graedel AT&T Bell Laboratories, Murray Hill, NJ 07974 The fragrance of a lilac is among the most wonderful things the world has to offer. Soft and delicate, it can he readily perceived within a few meters of the flowering plant. If the air is still, the fragrance may he detectahle tens of meters away. These properties are far from characteristic of all odors, however. The stench of decavine " " fish can evoke a muchmore intense response, and a t greater distances. Is this due solely to the orooerties of the odorant molecule? ~espite'yearsof research, the reasons why a certain molecule is odorous and why i t produces the sensation that it does remain obscure. Current attempts to relate olfactory response to various physical properties of molecules have had limited success; clearly this basic interaction between the odorous molecule and the nose is an important part of the issue heing explored here. However, a related topic is also important: eiven that a molecule is odorous. how does the nerceived intensity vary with the conditions'under which it'is perceived as well as with its intrinsic olfactory effects? A number of different parameters become of interest: the molecular flux from the source, the dispersion characteristics of the atmosphere a t the time and place of emission, the likelihood of atmospheric reaction of the odorant (thus eliminating or changing the odor), the minimum detectahle concentration of the odorant (the olfactory threshold), and the relationshin between odor intensity and odor concentration (the scaling function). Evaluating the factors involved in perceived intensity involves several different and seldom overlapping .. .. scientific fields: sensory perception, hotany, zoology, meteorology, and atmospheric chemistry. As will he seen, few molerules of interesthave been subject to suchdiverse research. Those that have, however, (particularly when judicious estimation is hrought into play) are sufficient to illustrate the factors of importance to olfactory response. Some of these molecules, their sources, and their effects, are examined below. Molecular Properties and Odor A molecule capable of producing the sensation of odor must make its wav to the olfactorv rece~torsof the nose and oroduce a signai that can he t r a n k i t c d to the brain by a sedsory neuron. Neither the transuort nor the sienal is well - oroduction . understood (I). lucida at ion of the latter involves knowledge of the mechanism of recentor interaction and neuron resoonse. a process as yet unsolved hy biophysical research. In lieu of this relatively direct route to understanding, many attempts have been made to relate odor sensations to seleded molecular nronerties that seem likely to be associated with odor nercepiion. Perhaps the earliest of these studies was the &relation of odor intensitv and molecular shave, the thinkine being that the receptors in the nose might begeometricall; designed so that certain molecules fit into them and evoke a response. Amoore (2) has done the most extensive work in this area, and has claimed moderate success in deriving odor-shape relationships. Recent statistical work by ~ckiffman (3) suggests that no significant correlation exists, however. Other studies have explored the chemical bonding properties of the odorous molecules. Davies (4) has correlated the heat of adsorption with odor intensity in an attempt to isolate the process of adsorption to an olfactory receptor. Some success resulted, although the correlations were not striking. Mazziotti ( 5 ) repeated the process with boiling points instead of heats of adsorption; the results remained suggestive hut not definitive.
The mowine availability of spectral data and other informationhavingtodo wirh ;he elertronicstructurc of odorous molecules has invitrd invrsri~ntionsof increasinals sovhis,ticated molecular properties. The resonant ;ibra$onal frequencies of molecules (6),their acid-hase character (71, and the directed molecular dipole (8) have all been proposed as correlation parameters; each has met with some success in explaining experimental data and probably reflects a different aspect of the efficiency of interaction between the molecule and the receptor. I t is common knowledge that reduced compounds of sulfur and nitrogen (e.g., hydrogen sulfide, trimethylamine, etc.) tend to have extremely high odor sensitivities. This characteristic is doubtless related in some way to the electron transfer properties of the molecules. Regardless of the mechanism of interaction between molecule and receptor, nothing can happen until the molecule reaches the receptor. This transport process may provide another means of discriminating among odorous molecules. Cain (9)has pointed out that the receptor sites are coated with mucous, through which odorous molecules must diffuse. Diffusion rates are far from uniform for all molecules, of course: they varv with molecular size. molecular shane. and the properties o ~ t h diffusion e medium (see, for exam&, ref. (10)). In this connection, it is of interest that Greenbere.. (11) . . has found some evidence for n rclatiunship between ~ h e o d u r s oroorrtv intenqitv ut'a moleculr nnd i ~ hvdmi)hohicitv. -.a . . " that may heielated to the ease of diffusion. The present state of research in olfaction is characterized by a plethora of tantalizing clues and a paucity of definitive results. We still do not know why some molecules smell as they do, and why others do not have detectahle odors a t all. McGill and Kowalski's (8) extensive statistical studies suggest that any one property of a molecule will he insufficient to explain its odor characteristics and that a t least two molecular properties, perhaps related to transport and interaction, respectively, must he taken into account. Until this can he done in a rigorous way, we are restricted to empirical generalities: sulfur compounds and amines are distasteful and sensed a t very low concentrations, cyclic and aromatic aldehydes and alcohols are generally pleasant smelling and have high threshold concentrations, the intensities of mixtures of odors are not sums of the components, and so on. The Mathematics of Odor Intensity
Once a molecule is recognized as heing odorous, regardless of what nsvchonhvsical orocesses are involved. the resnonse to it may de q u k & a t i v h y investigated. The first of the factors important to odor intensity is the olfactory threshold concentration Ct, the concentration at which a molecule is not only detectahle hut is definable as representative of the odor heing studied. The range of Ct values is very wide, indicating that certain molecules are detected with extreme sensitivity by the nose, while others must be present at very high concentrations to he noticeable at dl. For example, Hellman and Small (12) tested 101 petrochemicals with an odor panel and found that the concentration "at which 50%of the panel defined the odor as heing representative of the odor heing studied" ranged from 300 parts per trillion (ethyl acrylate) to 500 parts per million (ethylene oxide). This represents a range of more than six orders of magnitude in Ct. Once an odorant is detected, it becomes of interest to know how the perceived intensity (faint, strong, etc.) depends on Volume 61
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the concentration of the odorant. For an individual compound, much of the data suggest logarithmic dependence (13)
Finallv. i t is necessarv to consider the nossibilitv that the odorant kolecule may Lndergo atmosphkric chemical reactions and thus be lost through transformation. In the atmosphere the dominant reaction usually involves either ozone 1011addition at an unsaturated carhon-carbon bond. hvdroxvl ;a&cal (HO.) addition a t such a bond, or hydroxil;adical abstraction of a hvdroeen atom (22-24). Reactions with such ~ very much slower common molecul& as 62, HzO, i d C O are excent where the odorant is a free radical (in which case its c o n c k a t i o n will be very low). One therefore evaluates the removal rates by computing
where I is perceived intensity, C is odorant concentration, and k and b are constants which are specific to the odorant. Substantial support has also been presented (13, 14) for a power-law dependence Typical values of b are 0.2 to 0.7 (13). The simultaneous presence of more than one odorant complicates tn a considerable depee the relationship between concentration and perceived intensity. This complication will not he exnlored here: those interested will find details in the work of ~ r a v n i e k set al. (15) and Moseowitz (16). Another fador involved in the perceived intensity of an odor is the molecular flux of the source from which the odorant comes. The extremes in fluxes range from very small in the case of a flower to enormous in the case of volcanoes. If the source does not initially emit the odorant as a gas (as in the odorants emitted from animal waste, for example), the vapor nressure of the odorant mav need to be taken into account. i)ealing with this chemical aspect of the problem is relatively straiehtforward: however. for the Duruose of this discussion the quantity of interest is the gaseous molecular flux whether directly or indirectly emitted. Next, the dispersion of the odorant molecules by atmospheric motions must be considered. Techniques for dispersion calculations and extensive charts and tables have been given by Seinfeld (17) and Turner (18). H6gstrom (19,20) and Byrd and Phelps (21) have discussed dispersion for the specific case of odorants. The basic approach is to assume that the "plume" of odorant molecules will distribute itself with Gaussian functional dependence of the concentration; this assumption has been shown by numerous field studies to be reasonable. The odorant concentrations is then given by
r = kRC
where R is the concentration of either O3 or HO. and k is the rate constant for the reaction between that reactant and the odorant molecule. The limiting mean lifetime ( 7 ) of the odorant molecule due t o the dominant reaction is then r = (kRJ-1
.
-
7
< 0.1 5
(7)
U
Mathematical assessment of odor intensity thus involves determinina for a s~ecifiedmolecule emitred a rlistancex from the observkr the source strength Q, the mean wind speed u , the ~ l u m eitandard deviations a, and a,. and the limitine chemical lifetime 7 . The resulting concekration C is then computed from eqn. (3), diminished if necessary by a reaction loss factor. If C is less than the odor threshold C , the odorant will not be detectable. If C exceeds Ca the perceived intensity may be evaluated from the appropriate relationship for the molecule, as in eqns. (1) and (2). Perceived lntensltles of Selected Odorants T o demonstrate the interaction among the factors mentioned above, five examnles have been selected. These examples have two distingt;ishing characteristics: they are sufficientlv well studied that all or most of the reauired data are availabie or can readily be estimated, and they are sufficiently common that the results can be verified against everyday experience. The examples are identified and characterized in the table. Inspection of the tahle reveals that a difficulty with olfactory analyses of this type is that all the data needed are seldom available (even in this group of carefully selected examples). Prohletns of estimation can he left until later, however, since for the first example to be studied, Douglas fir trees, the data are complete. As a sample calculation, assume a cluster of ten trees being observed on a partly cloudy summer day with a moderate (3 mls) breeze. The source strength is lO(140 ~ g / s ) = 1.4 X 10-3 gls. For an observer a t a distance of 5 m down-
(4)
rcyczu
(6)
If this lifetime is significantly shorter than the transport time between source and ohserver a t the mean wind meed that exists, chemical reaction loss will influence the perceived odor intensitv. A eood rule of thumb is to include chemical reaction consideration if the following inequality is satisfied
where Q is the source strength, x is the distance from source t o observer, h is the height of the source above the ground, u is the mean wind sneed. . .and a" and a, are standard deviations of the crosswind and vertiLal concentration distributions within the plume. The u values are functions of distance as well as atmospheric and surface roughness. (The equation is invalid a t zero wind speed, a situation in which the concentration decreases due to molecular diffusion rather than bulk turbulence.) The a values are functions of cloud cover, wind speed, and time of day and can be estimated as discussed by Turner (18). As written, the equation is valid for an observer at ground level, directly downwind of the source. If the source is a t ground level also, eqn. (3) reduces to
Q C(z) = -
(5)
Parameters for Perceived Odor lntenslty Calculatlonr Primary Odwant
Molecule
Swce Apples Lilacs Decaying Fish Douglas Fir Trees Striped skunk
Reference
han+Z-hexensi l-hexanol himethylamine a-pinene crotyl mercaptan
(34) (36) (36) (39) (29
Source Slrength Flux pg/s Reference
...
... ... 140. 20r
... ... ... (40)
...
Odor Threshold
G ppb
Reference
...
...
90
(1 3
1 6 0.015
(32) (4n (30)
Atmospheric Reaction Rate Reactant Constanta Reference
HO. HO. HO. Oa
HO.
... ... 6.1 X 8.4 X
lo-" lo-"
...
... ... (43 (4.3
...
aPermePadloiwmof5m. Unit* are cmSmolec-' J-1. " A typical quanti of skunk discharge 1s a few ml(29). me otrength estimate asovmes mat 2 ml of that discharge is crotyl marcaptan and mat vamrllation lakes place over a period of one hour. The souce strengm fw iswmyl mercaptsn will be somewhat higher since n is the mort abundant molecule in the skunk discharge.
682
Journal of Chemical Education
,011 Figure 1. Evergreen hees such as Me Douglas fir emits variety of terpenes, or-pinene onen being the most abundant. Asdescribed inthe ten, it is sbaightfofward to calculate the decrease of a-dnene wncentratlan with distance downwfndw a n me wuce A m p n e r r mndrt ons assbmed are Uws of a Ight. steady w~ndatmdday, wtm a paniy clauoy sry and an ozone concentrat on of 50 ppo The decrease Is due ch~eflylo atmospner%dtspers on,almosphmc chemical reactionshave a negligible effect. The odor threshold is the concentration at which or-pinene can be detected by 50% of the members of an odw evaluation panel. in this example, where a-pinene is present at the source at a concentration exceeding 1 ppm, its concentration decreases below the olfactory threshold at s distance of about 16 m.
wind, the a,. and oz values are 82 cm and 50 cm, respectively (18).Equation (4), then, gives for the concentration of a-pinene
0
I 20
h
40 60 80 OOWNWiNO DISTANCE ( M I
i
Figure 2. The ador of the striped skunk is primarily due to isoamyl mercaptan, a ~ h lmerceotan. l and ban$2-butenevl methvl disulfide in its scent. In this fiowe. the Concentrat ans of soamyl mercaptan and crotyl mercaptan (tho pr n c m l odorant mo.ecuies of the str pea sxunkl are mown as a f.ncllan of downwma dlslance Moleoroiogcal mndnrons. ndemtca wnh h s e dsed to mnstnn F g.rc 1, are characteristic of moderate convective mixing and dilution. The cancennation decreases below me isoamyl mecaptan olfactory threshold at a distance of about 7 m and below that for crotyi mercaptan at about 35 m.
for O3 (25) and 4 X 10-5ppb for HO. (26,271. For ozone, the result is
rnol
X -= 2.7 X 10-l2rnol 138g
Air, with a density of 1.2 X 10-3 and an average molecular rnol cmF3 a t weight of 29, has a concentration of 4.1 X ground level. The mixing ratio of a-pinene is thus given by
cmcsm)=
2.7 X 4.1 X
rnol
low5rnol
= 6.6 X loT8 or 66 ppb
Since the olfactory threshold for a-pinene is 6 ppb, the fragrance of the Douglas fir will readily he detectable if the a-pinene concentration is not diminished by atmospheric chemical reactions. To investigate this possibility, the-mean chemical lifrrime for a-pinene must be c o m ~ u t r dby ean. (6), given the rate constant from the tahle. he calcu~latibnrequires that the concentrations of the reactive molecules he known; typical values in nonurban environments are 50 ppb
where the conversion factor expresses the density of air in molecules per cubic centimeter. It is clear that the lifetime of the a-pinene molecule is very much greater than the travel time from come to observer of about 2 s. The chemical lifetime for ~ - ~ i n e with n e respect to the hydroxyl radical is even longer. (The rate constant has also been measured.) Thus, atmospheric reactions do not perturb the C(5,) value given above. For some terpenes the ozone rate constant is higher than for a-pinene (28), however, and ozone reaction may compete with dispersion, particularly on days with very little atmospheric mixing. By repeating a t different x values the procedure outlined above, a graph of odorant concentration as a function of downwind distance can he constructed, as shown in Figure 1. Dispersion causes the concentration of a-pinene to decrease rapidly with distance, reaching the olfactory threshold a t a distance of about 16 m. A second example is provided by the scent of the striped skunk (Fig. 2). The scent is composed primarily of three orVolume 61
Number 8 August 1984
683
1 1
01
/
I
,
I
#
,
10 IW DOWNWIND DISTANCE (M)
I
,
I
I
ganic sulfur compounds (29): 3-methyl-1-butanethiol (isoamyl mercantan). trans-2-hutene-1-thiol(crotvl . . merca~tan).and trans-i-butenyl methyl disulfide. Olfactory thresh& the first two have been determined (30). The source strenzth can he estimated trom available information (see tahle) i n d the concentration-distance function calculated. The results for isoamyl and crotyl mercaptan, the two most abundant constituents, are shown in Figure 2: they provide an interesting demonstrntion of the interplay hetween concentration and olfactory threshold. Although isoamyl mercaptan is the more ahundant, its con cent rat in^^ decreases below C , at a distanre of about 7 m. Thereafter, the perceived odor is due to crutyl mercaptan, and is detectahle t o distances of 30-40 m. Such a distance, several times larger than that for the Douglas fir trees, is a consequence of the very low olfactory threshold of crotyl mercaptan. Note that the crotyl mercaptan concentration is ten times that of the threshold at a distance of about 18 m and one hundred times threshold a t about 5 m, a dramatic increase with increasing proximity! Since the rate constants for the reactions of crotyl mercaptan with ozone and the hydroxyl radical have not been experimentally determined, how can one he sure that they play no role here? I t turns out that it is possible to estimate these rate constants with a moderate degree of accuracy (e.g., ref. (31)). The reaction with HO. is expected to dominate, and to proceed by metathesis of the thiol hydrogen atom. The rate constant thus estimated is kzs8 =5 X lo-" cm3 molec-1 s-1. This gives a chemically limited lifetime of T = 2 X lo4 s. As with a-pinene, this is so much greater than the travel time that it can be disregarded. In addition, i t should be noted that the difference between the two times is so great that an error in the value of the estimated rate constant would not affect this
for
Journal of Chemical Education
I
100
Figure 4. The fragrance of the essence fromDelicious apples isdue primarily to KanpBhexenal,whose concenbatian decreases rapidly with distance.
,
Figve 3. Alewife awash on an lllimis beach. The molecule primarily respnsible forth= odn of decaying fish is Wimethylamine. whose decrease in ConcenWation with distance is shown here.
684
I
10 DOWNWIND DISTANCE lcrn)
conclusion. If instead a rate constant equal to the highest ever measured for anv reaction of this tvve had been assigned (k = 1X 10-10 cm3 kolec-1 s-I), atmospheric chemical reactions would s t i i play a negligible role over the time scales of interest here. Indeed, although occasional exceptions such as ozoneterpene reactions may occur (as noted above), lifetimes of a few seconds or less will generally he obtained in the atmosphere only for reduced free radicals which combine with molecular oxygen (22). For stable species, therefore, atmospheric chemistry is seldom of consequence for odor considerations. A third illustration of the interaction of source strength, meteorology, and odor threshold is that of dead and decaying fish. Although several amines are involved in the perceived odor of decaying flesh (the unequivocal common names for 1,4-butanediamine and 1,5-pentanediamine being "putrescine" and "cadaverine," respectively), trimethylarnine appears to he the primary odorant (32). The source strength is not known, hut an estimate for a typical occurrence can be made as follows. First, assume a thousand two-pound fish have been washed uo on the heach. Second. set an a ~ ~ r o x i m aUDDer te limit to t i e emission. Since about2% of the &eight of the fish is nitrogen (33). if a tenth of the nitroaen avnears as trime15-day decay period the resulting flux will thylamhe be 2 X lo4pg s-1. When this substantial flux is combined with the relatively low olfactory threshold of 1pph (table), the odor is detectable several hundred meters away (Fig. 3), a result consistent with the personal experience of those who have encountered such situations. Atmospheric reactions, computed with measured rate constants, are again much tw slow to be of significance. Unlike the example provided by decaying fish, many natural odors can be detected only very near their source. Among the many demonstrations of such a case is that of apples. Apples contain a t least 40 volatile molecules, the most abundant being trans-2-hexenal (34). Even trans-2-hexenal, a
eve; a
rather common constituent of vegetation (:15) is not present in meat dundance: Schultz et al. (.34) measured 295 me of the compound in 1000 g of apple essence a t 150-fold concentration. This amounts to about 0.4 pg of the compound in a 200-g apple. T o estimate the source strength, assume that the apple is crushed and the essence allowed to escape over a 5-min period: the resulting source strength for tram-Lhexenal is 1.3 PC:s-l. Figure 4 shows the resulting wnrentration-distance diagram. The odor threshold for trans-2-hexenal has not been determined, hut threshold values are available for several other aliuhatir and olefinic aldehvdt.~.That information is sufficieni to predict a Ctrange witgin which the desired value is verv likelv to occur: this ranee is shaded in Fieure 4. The figureprediks that the fragrance of an apple s h h d he detectable a t a distance of a few centimeters, a result consistent with everyday experience. As was done ahove, the rate constant for chemical reaction can readilv he estimated and reaction loss shown to he negligible within the odor perception distance. This example demonstrates that it id possil~leto derive g o d estimates of olfactory effects starting with no information other than the identity of the odorant molecule. Source strength (or lower and u w e r limits to it) can often he estimatei, the approximate odor threshold assigned by analogy, and the atmospheric chemical reaction rates assigned by thermochemical kinetic principals. In the examples descrihed ahove, a source strength, either measured or estimated, has been used to calculate the distance within which an odor can he detected. Another way to approach the calculation is to measure the distance and d c u l a t e the source strength. This can he done, for example, for lilacs. Although the primary fragrance of lilacs is 1-hexanol, with contributions from several other molecules (mostly alcohols (36)) the source stren@th has aunarentlv not been determined. ~ o k e v e rthe , fragra&e of lii&s in hfoom is commonly detected a t distances of 5 m or so. Under the most suitable meteorological conditions, the range may reach 10 m. If 7.5 m is thus chosen as appropriate for the meteorology considered in this study, 7.5 m will he the distance a t which the concentration of l-hexanol is equal to the olfactory threshold of 90 pph. (Once again, the rate constant assigned to the reaction of 1hexanol with the hvdroxvl radical renders chemical reactions unimportant.) ~ u b s t i t u k o ninto eqn. (4) gives the source strength, Q = 3200 pg s-I. This seems rather large when compared with the other source strengths and implies either very vigorous emission of l-hexanol or the presence in the fragrance of an unidentified molecule with a much lower olfactory threshold. he examples presented ahove have assumed the correctness of the Gaussian plume model descrihed by eqn. (3). Strictly speaking, however, that approach is validnotfor the several second response time of the nose, hut for very long averaging times under constant conditions. A more realistic situation is descrihed by Hogstrom (19); an adaptation of his sketch is shown in Figure 5. The concentration fluctuations are created by a combination of varying rates of emission of the odorous molecules and by the inherent turbulence of the atmosphere. The nonlinear response of the human nose to odorant concentrations ahove the olfactory threshold exacerbates the problem. Hogstrom approached this complication by modifying the standard deviations in eqn. (3) so that u:=u&+u%
(8)
the first term being the variance in the mean instantaneous concentration of the odorant and the second heing the variance in the distrihutinn of the loms of the plume centroid. (A similar eqnation applies to a,.) Dttterminatims of the centroid terms fur different time scales and different ;tahilit\. conditions are rare: thus the approach is difficult to apply. Where it has been done (191, the predictions are reasonably good
within one or two kilometers of the source of the odorant and less satisfactory at greater distances. More work is needed to properly predict odor intensities on short time scales and a t great distances. Discussion The specific examples presented ahove lead to several more general conclusions. The first is that the distance to which an odor can he detected is due ru the mterplay hetween the source strength, the olfactory threshuld. and the turbulence of the atmosphere The fragrances that we assoc~stew t h flowers and other botanical sourws are grnerally escers, aliphatic alcohols, or aldehvdes. The olfilotorv thrr.;holds tend to he within ~ ~ -the ~~- -range 0.;-10 ppm and thlfragrances are seldom detectable a t distances greater than a few meters even if the source strength is large. Natural odors resulting from decay or defensive scents are eenerallv amines or sulfur-containing molecules. The olfactory thresholds for these molecules a; quite low, usually within the range of 0.1-10 pph. As a consequence of these low thresholds and of the relatively high source strengths that are often oresent. this class of odors is often discerkhle tens or hundreds of meters from the source. All of the odorous molecules are susceptible to chemical reactions in the atmosphere. These relatively large and chemically stable molecules do not react with great rapidity, however. As a result, it appears that meteorological dilution of odorants will always exceed chemical loss as a mechanism for concentration decrease. Although the distances a t which odors can he perceived have been discussed in some detail, little quantitative information has been given concerning the intensity of the odors within those distances. The omission is due primarily to a paucity of determinations of the constants in eqns. (1) and (2) for different odorant molecules. I t is of interest, however, to suhstitute for C in eqn. (2) its equivalent from eqn. (4). giving ~
~~
~
~
~
~
(9)
Noting that ay and uzare each proportional to the distance x at distances less than a few hundred vards and that a tvuical .. value for b is 0.5 (131,
The perceived intensity is thus roughly proportional to the square root of the source strength, inversely proportional to
m HOURLY
- - - ---- -
0
0.5
1 .O
TIME (HR)
Figure 5. A schematic diagram showing how the concentration of an odorous substance Can exceed the odor threshold several times during a period when the hourly mean is much below the odor lhreshold (adapted from Fig 1 of Ref. ( 19)).
Volume 61
Number 8
August 1984
685
-
~
the distance between source and observer, and inversely proportional to the square root of the wind speed. Quantitative information on the emission, dispersion, and detection of odors is vital for some applications, important for others. In~manv. wavs. ~ and~interestine ~ ~ for all. - . however. the qualitative aspects are at least as important. This article has discussed in some detail the mathematical and atmospheric aspects of the subject, which are useful in such diverse fields as botanv and air nollution analvsis. Although the auestion, "Why ddodorous kolecules smeh as they do?r,"remainsto he answered. studies such as those described here can say much nlmut thirelawd question;.What cnuies the vast ditferenrw in the perceived intensities otodor~,usi n o l e c u l e s ? "
.
~~~
-
~
(16) Muscowitz, H. R.. "Odor Qualily and Chemical Structure," (Edifora: Mcneowitl, H. R., and Wanen, C. B.J. ACS Symp Sar. 148,Amrr. Chem. Suc., Washington, DC. 1981,pp. 2b55. (17) Seinfeld.J.H.."AirPollution:PhysicalandChemicalY~~d~m~~Lats."M~C~~~-Hill, New Ymk, 1975. pp. 31C-313. (18) Turner. D. B., "Workbook af Atmmpheric Dispersion Minutes." Publication 999AP-26. Natl Air Pullut. C o n k Admin., Cincinnati.OH, 1969. (19) Hagsrrdm, U.,Amos Enuirun.. 8,103 (1972). (LO) Hdgstrom, U.. "Hums" Respunsrs to Envir"nm.ntsl odon," (Editors: Turk, A,, Johnston. J. W., Jr., and Maultoo. D. G.), Academic Press, New York, 1974, pp. 163-198. (21) Byrd. J. F.. and Phelps, A. H., Jr.,"AiiP~llution," IEdilo~:Stem, A. C.J. 2nded..vol. 2, Academb Prrss, NewYork. 1968. pp. 306327. New York. (22) Cmedel, T E. '"Chemical Complundz in the Atmcnphere," Academic P-, 1978. (23) Hendry. D. C., and Kenley, R. A,. "Atmoapheric Reaction Products of Organic Communds," Repun EPA-560/12~79-W1. Environ. Prutcction Ayemy. Washington, DC. 1979. (24) Atkinnun. R. A.,Darnall, K. R.,L1uyd.A.C.. Winar,A.M.,and Pifts. J. N., Jr.,Adu. Pholoehem.. 11.39511979).
Literature Cited (I) Gsstdand. R C., "Handhukof Sensory Phyaiolugy. IV. Chemical h 8 a .I: Olfmtion," (Editor: Beidle,, L. M.), Springer-Vadsg, Bedin, 1 9 7 1 , ~132-150. ~. (2) Amoorc, J. E., "Molecular Basis of Odor." C. C. Thomas Co.. Springfield, IL, 1970. (3) Schiffman, S. S.,Science, 185,112 (1974). (4) n a v. i~ es . I -T of Senrnrv Phvaioloev. N. Chemical Ssnses. I. Olfaction." ,., ~~, , .'Handhmk ~ ~ (Editor Beidler, L. M.), Springer-Verlag. Berlin. 1971, pp. 322-350. (5) Mscciotti, A.,Notwe, 250,645 (1974). (6) Wright, R. H.,"The Science oESmell." BasicBwks. New York. 1964. 171 Brower. K. R.. and Schsfor. R.. J . CHEM EDUC..52.538 (1975).
~~~~~~~. ~.~ -. ~
~
(10) Stannett, V., " D i n d o n in Polymers," (Editom: Crank, J.,snd Park. 0. S.), Academic Press. London. 1968. pp. 41-73. (11) Greenbcrg, M. J., ,"Odor Quality and Chemical structure," (Editors: Moocowit.. H. R., and Warren, C. B.), ACS Symp. Ssr. 148, h r . Chem.Soc., Wsshington.DC. 1981. pp. 177-194. (12) Hellman, T. M., and Small, F. H., J. AirPolluf. Contr Aaaoc., 24,979 (1974). (13) Cain, W. S., and Moscowitz, H. R, "Human Heapone4a to Envkanmenfsl Odors," New IEdiiors: Turk.A.. Johnston. J. W.. J L s n d M0ulton.D. . G.l.Aesd.miePreaa. . ~ m k1974. , pp: 1 2 2 . (14) Dravnieka, A , and O'NeiU, H. J., Amen I n d Hyg. Aasae. J., 40.85 (1979). (15) Drsvnieka. A,, Bock, F. C.,andJarkk,F. H . . " O Structure." (Editors. Mmcowilz, H. R. and Warren. C. B.). ACS Symp. Ser. 148, Amer. Chem. Soe.. Wsshington,DC. 1981,pp.7941.
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