Smells contribute to urban identities ^1–3. They are memory activators ^{4, 5} and, as the neuroscientist André Holley points out, they have striking emotional power. Nevertheless, the link between their hedonic aspect and the nature of the emotions generated is not direct. I will argue that to understand the workings of the sense of smell, temporal data is as important as spatial data, and that mental images, including olfactory ones, participate in the overall sensory apprehension ³. In other words, because an odour is an object of interpretation, its rejection or acceptance does not rest on its sensory characteristics only. Drawing on diversified personal field work and research ^{3, 6–9} about smells as they deploy themselves in inhabited spaces, and on publications in different disciplinary fields, this paper seeks to explore the relationships of cities to emotions generated by smells. Firstly, it will offer explanations about how urban odours may shape emotions, the importance of various characteristics of the sense of smell will be weighed underlining the importance of smell references in urban’s odour generated emotions. It will then consider how liking and disliking smells might shape urban experience. Because odour-generated emotions may contribute to the indispensable readability of the places in which we live, the conclusion will draw attention to the necessity of taking smells into account in urban planning.

Urban odours that shape emotions

Breathing odorous air

An odour is a sensation generated by the encounter between specific chemical compounds and a particular organ, which provokes a sensation. It is subject to interpretation on multiple, entangled levels: hedonic, semantic, reminiscent, and emotional. Even if the smelled odour is labelled as “good,” its meaning may lead to negative interpretation or emotion, and vice-versa. For example, some inhabitants of the Huchette district in Paris no longer tolerate the smell of grilled meat from the Greek restaurants. It penetrates all the dwellings on the street a every night and day. Even if these smells are considered as positive in French culture, their pervasive and recurring presence seems, here, to provoke a negative interpretation ².

In this sense, the standard classification of smells as “good” or “bad”, automatically generating pleasant or unpleasant corporal and emotional states, does not necessarily work. Extreme intensities excepted ¹⁰, the hedonistic interpretation of odour does not rest exclusively on the nature of the chemical signal itself. When urban odours shape emotions, the nature of the chemical compounds is only a part of it. Different elements, in the context of the act of smelling, may intervene: notably the habituation phenomenon, social and cultural contexts, imagination and associative learning.

Habituation is a phenomenon of sensory fatigue common to all sensory modalities. However, as we will see here, its olfactory specificities have important consequences in ordinary daily odorous encounters ¹¹ and for the construction of emotional-olfactory urban images and attachments. Habituation, or immobility in a stable (or very slowly changing) volume of odorous air results in a very low level of olfactory perception, or no perception at all, provided that a new odorant event does not occur – such as a sudden increase in the odour’s intensity or the appearance of a new odour. While emerging from the odorous volume allows us to smell a new air, a period of time of a length related to the previous time-period of exposure is necessary in order to regain sensitivity, thus allowing us to to re-evaluate the air we were previously accustomed to. Recovery after habituation can then be linked to the spatial scale of the subject’s movement: the greater the distance (temporal and/or spatial) from a familiar air, and the greater the chances of smelling the air again upon return to a familiar place. Put differently, it is the ‘scale’ of the journey that makes it possible to go beyond the threshold of personal habituation and make a renewed discovery of the smell. In interviews about ordinary smell experiences of places ³, people regularly evoked the (re-) discovery of “unsmelled” odours, be it after shorter or longer periods of time; for example coming back into a classroom after a few minutes or into one’s own home after days or weeks.

The global context of the act of smelling, the “conjugation of the senses,” as David Le Breton ¹² calls it, is also of importance. The nature of the source of odour and the way it is considered in a certain place and time, its social and cultural contexts, weigh on the interpretation of the olfactory sensation. Melanie Kiechle ¹³ reports, for example, the destiny of the ailanthus (Ailanthus altissima, now known in Europe as an invasive tree) that had been erased from New York City at the end of the 19^th century because of its supposed toxicity, a consequence of its pungent smell ^14–16. The idea of odour as a nuisance is therefore at the crossroads of several societal, technical and symbolic issues and, as Constance Classen and her colleagues ¹⁶ express it, when there is a smell conflict, “it is often a question of applying vague laws to a poorly understood problem.” Valid reservations such as theirs aside, it can be said that emotion takes place within the body. Social and cultural contexts do not account for the whole emotional impact of particular, situated odour.

Associative learning is a process by which distinct events are linked through their perceptual simultaneity. This Pavlovian conditioning phenomenon involves an emotional variant in which a neutral stimulus acquires the affective valence of another stimulus. It is called evaluative conditioning, and it explains how a neutral odour may acquire a positive or negative valence, depending on whether it is associated with pleasant or unpleasant events. Gesualdo Zucco ¹⁷ points out that unlike the classical form of Pavlovian conditioning, in the case of odour this emotional conditioning: a) can be established from a single occurrence, b) is particularly resistant to the phenomenon of extinction, and c) the relation between emotion and odour (or the whole chemical context) often escapes awareness. Such a phenomenon may be linked to Antonio Damasio’s reflections ¹⁸ on the entrenchment of emotional states – and decision-making – in bodily states. These somatic markers could explain how odours previously associated with happy or unfortunate events may trigger physiological reactions even before consciousness emerges. Jacqueline Blanc Mouchet, a specialist of odour staging in cultural or marketing contexts, reported to me ³ that an odorized phone booth with a sea scent triggered a panic reaction from a user. This person had had a childhood experience of drowning.

These specificities of associative learning when it comes to smells may also explain why, in public places, smells can easily be considered with suspicion, given the awareness that it is possible to manipulate or to introduce odours into a space¹⁹ . Furthermore, evaluative conditioning would be implemented much easily for negative events. Franck Baeyen ²⁰ and his colleagues see this phenomenon as a predisposition of humans to effortlessly acquire adverse or harmful associations compared to positive or harmless ones. They name it emotional asymmetry. Thus, smell depreciations are often vehemently expressed, and many urban studies on odours focus on negative smells or “olfactory pollution”, forgetting that even those can contribute to urban olfactory identities and attachments.

On the importance of cities’ olfactory images of reference

Because of the habituation phenomenon, the modalities of smell encounters are specific. They depend on the environments smelt previously in the smeller’s life, i.e. their status regarding the whole smell-place situation. Thus, the ordinary experience of odours in the city cannot be reduced to lists of sources of odorous compounds and to their perceived intensity. To describe these explicitly or implicitly expected smells in daily smells encounters ⁶, based both on interviews about smell-spaces and on smell walks in public places, I suggested the concept of olfactory image of reference. In any ordinary smell experience, the odour is compared with an olfactory mental image of the places, moments, and events. The fondness felt for “normal” odours of places is then built on the repetition of localized smell encounters, leading to the elaboration of olfactory images of reference. On the contrary, when the odour does not “fit” – what Egon Köster and his colleagues call an olfactory misfit, in their MISCORP theory ²¹ – it may lead to a negative evaluation of the whole olfactory situation. The divergence between the reference and what is smelled in the moment can generate a feeling of unease because, as an interviewee said, “it doesn’t match”.

These olfactory images of reference are not only linked to spaces but also to moments in time; the attachment to urban olfactory identities is tie to specific moments. When they are generalized in space and punctual in time, the odours become the period’s identity for this given town. These can be ecosystemic events, such as large tides or massive blossoms, or anthropogenic events, such as a widely shared odorous activity – simultaneous combustions of burning the same heat source or industrial process of significant intensity. The intertwining of odours from human activities and those from over biotopes can define time-situated urban olfactory identities.

Typically, food is at the heart of the encounter between a territory (often a place of production) and a city (a place of consumption). Despite the “coca-colonization” ²² and other globalization processes, locally consumed foods often remain associated with local cultural and biological frameworks. The olfactory rhythms of food are at the crossroads of natural and constructed times. With their local and temporal characteristics, cooking smells are likely to participate in cities’ affective odour-related identities, to be considered fondly familiar elements with both spatial and temporal specificity: when the same dishes are simultaneously cooked all over the city, the smell lends definition to a space and a moment. The Chicago Barbecue Festival, the Feria of Nîmes (and its paellas and grills) are examples of such temporal olfactory identities. One could also mention the Chimaek Festival of Daegu in South Korea, or its Chinese equivalent in Ningo, where hundreds of thousands of people consume fried chicken drizzled with beer. Apart from festive times, this type of temporal marking can be linked to the seasonal availability of certain foods and the traditions of consumption, also seasonal. Bak ²³ reports, for example, that at the beginning of winter, public transportation in Seoul have a smell related to the many boxes of kimchi (cabbage fermented with chili) that circulate within families for their annual consumption.

As the act of smelling takes place in a context, the olfactory identities of places depend not only on specific mixture of odorous compounds but also on their distribution in space and time. More specifically, these distributions’ spatial and temporal scales condition these identities. The repetition of olfactory encounters constructs reference olfactory images of cities and their olfactory cycles. They impregnate bodies with emotions in implicit or explicit loops. Nevertheless, if the odours of cities have the ability to shape emotions, we may wonder whether, in turn, the emotions generated by smells should be considered a necessary parameter for urban design.

Odour emotions shaping the urban?

Accepted or rejected odours sources

Wanted, accepted, tolerated, or rejected odours shape affective relationships with cities because they convey memories and mental images. Even before the Covid-19 pandemic, the air had an anxiogenic power, linked to the idea of the invisible menace ^14,24. At some point, odour became an expression of this menace. Even if later on the idea of illness conveyed by smell was debunked, or pasteurized to use Corbin ³ expression, the idea of odour as a sign of danger still seems real. ³ Pamela Dalton ²⁵ points out that growing public concern about health risks from odour exposures can “amplify vigilance and attention to even low-intensity, neutral odours.” It would explain why many contemporary concerns crystallize around exposure to odours, including those of perfumed products ^{26, 27}.

It should also be stressed that the perception of air quality as healthy or unhealthy is not entirely detached from its perceived smell; event in the WHO health definition, the notion of discomfort is considered a definer air quality. Thus, for the WHO, if more than 2% of the population feels discomfort with an odour, then it can be considered as a nuisance that will have health impacts. The feeling itself of being exposed to a health hazard can, it seems, have physiological consequences.

The recurring presence of smells, whatever their origins, may disturb activities and upset the sense of safety. It is then necessary to consider further the contexts of the notion of olfactory nuisance. First, the very definition of “olfactory pollution” needs to be questioned, especially outside strong intensities. Concerning “bad smells”, Constance Classen, David Howes, and Anthony Synnott ¹⁶ distinguish different kinds of “urban domains”. In industrial areas, unpleasant or repugnant odours are considered legitimate. Though there are exceptions, for example for food odours, in general in public spaces such as residential areas, commercial and recreational, the olfactory regime tends to neutrality because odours considered negatively are usually banned from them by local regulations. Thus the interest of the FIDOL approach (Frequency, Intensity, Duration, Offensiveness, Location), used to address the acceptability of odours in recent olfactory nuisance studies: an odour is likely to be considered a nuisance if it is sufficiently frequent, intense, present for a long time, very unpleasant qualitatively, and in contradiction with expectations for the place in question. The distribution of economic activity concentrations can be a factor with respect to smell identities at all scales: notably industrial areas with multiple sites, as well as places in which there is a density and frequency of other particular land uses. Similarly, the smell’s symbolic significance should be taken into account. There are different examples of industrial activities’ smells positively considered by their neighbourhoods as signs of economic prosperity (paper pulp, fertilizer).

Nonetheless, the hypothesis of an urban organization controlled by olfactory nuisances, promoted by authors such as Robert Dulau ²⁹, remains to be proven. Historical research such Nathalie Poiret’s ³⁰ on the urban evolution of the city of Grenoble, cites sources that evoking the city’s most intense odours to affirm that there was no correlation there between the two. On the contrary, Melanie Kiechle^13,31 points out some New York City urban planning changes were linked to industrial odours and exhaust fumes at the end of the 19^th century. More research of this kind would be needed to prove or to temper the assertion that, in the past, urban planning developments were dictated mainly by odours. Some additional research would also be warranted to test the hypothesis of John Urry ³², according to which the advent of skyscrapers in Chicago was linked to their usefulness in escaping the smells of the city’s meat industry. New historical sources concerning odour and air quality would probably be required in order verify that we are not confusing our own understanding with those of the past. Let us not forget that these original skyscrapers are contemporary with the first air-conditioning systems, at a time when it was considered that air-cooling was equivalent to air renewal ^{33, 34}.

Urban olfactory identities

If odours can be a source of anxiety or discomfort, they can also generate pleasant emotions, not only when they summon pleasant memories but also when they appear in adequation with a given time and place, i.e., when they correspond to reference olfactory images. The attachment to olfactory identities of cities is then built on the spatial and temporal repetitions of smell encounters, leading to positive reference olfactory images. Regarding the construction of these urban olfactory identities, three essential elements should be considered: space (the size of the smell zone), time (the duration of the odour and its evolution). In addition, the status of the smeller with respect to the place must be considered: the scale of his or her movement affects the possibility of smelling – the farther away a smeller travels from his or her usual territory, the more differences will be perceived.

The larger spatial, olfactory scale, that is what Lucienne Roubin ³⁵ calls “odorant territory” and what Victoria Henshaw ¹ calls “macro-level smellscape” constitutes a permanent background, present always and everywhere within the area corresponding to this scale, an example of which would be the smell of vehicle exhaust pipes throughout a city. However, at this macro level, the background could be widely present without being all-encompassing – more episodic, such as the smell of the tide in a port city or that of a factory, whose processes that generate odours are limited to weekdays. This scale of a global smell identity is something that its permanent inhabitants barely notice. They recognize and evaluate them only after long periods of time away. It is the dimension of almost continuous immersion, which leads to what I have called over-habituation ¹¹, namely the difficulty in perceiving the odorant compounds in which one is immersed over long periods. Paradoxically, an attachment toward the smell-identity of a city can only be formed on the condition of leaving it and returning to it regularly. For example, a woman said during a field survey that she felt like she had arrived in Provence at the very instant as she rolled down the windows of her car at the toll station on the highway, smelling the characteristic air of the place. Another example involves the association of an industrial smell (that of viscose production) with the town she used to go to for her dental appointments as a child.

Closest to the smellers’ bodies is the proximity level that Henshaw calls micro-level smellscape. It corresponds to odorous events accessible, if only potentially by sight, or that are “within range.” When the odour scale of a given source is small but very stable over time, such as a bakery open seven days a week, the result is an odorous “punctuation.” In this case, it is likely to become a spatial landmark tied to the scale of the movements within the urban area in question. The idea of a cross-section representation that Henshaw uses to describe certain odorous phenomena is noteworthy, especially at the scale of the body. The height of emission of the odour can, in some cases, be crucial. Topography and street profiles can significantly affect encounters with smells. At this level, the odours’ sources are easy to identify and to name. The attachment in such a case is tied to odour cycles. For example, the odorous zone may, when it comes to the tide, depend on corresponding weather conditions, and for an industrial plant, on variations in the production processes.

Between the odorant territory and this micro-level lies an intermediate one, or medium-level smellscape ¹, articulating these two spatial scales. At this middle scale, typical smells are associated with a somewhat broader area, and the odour experience is considered vary over time. Smells are perceived as intermingled and thus components of the temporal and spatial identity of the city. Highly frequented spaces thus present particular challenges. In them, larger and smaller spatial levels meet: the odorous territory and the sphere of proximity. For this reason, the olfactory organization of public spaces should be thought out as carefully as possible.

If such spatial distinctions make it possible to think through the olfactory dimension of lived environments at various scales, including those of urban planning or architecture, it should be stressed that these scales are intertwined, and that spatial thinking cannot remain focused on a single spatial or temporal scale.

Conclusion: toward an affective smell design for cities?

The olfactory identity of a town is a unique combination of multiple sources arranged in specific spatial patterns of space and time. Through these, urban odours contribute to the attachment of people to the places they live in. They are parts of each city’s sensory identity, and they can shape emotions. They constitute spatial and temporal landmarks, helping their inhabitants recognize where they are and what time it is. They thus offer a kind of handle on the reality of the city. Reciprocally, smells that are liked and disliked shape the urban smell environment, typically in the relegation of the least tolerated smells to the edges of cities. For all these reasons, Odour-generated emotions should be taken into account in urban planning.

Much exploration still needs to be done about smell as an environmental component of places and, inversely, about places as material configurations more or less favourable to smelling. Olfactory considerations tend to be limited to global strategies seeking to limit discomfort and do address cities’ and territories’ olfactory identities. Nevertheless, these identities are regularly evoked, for example, as touristic assets. Odours contribute greatly to the sense of place. Inversely, rethinking space by smell can be a way of reinterpreting forms of spatiality. These are linked to the scales of movement that condition olfactory encounters, ranging from familiar and (re)cognizable to the unexpected or even the novel. Similarly, reference olfactory images, whether associated with places, moments, or events, may constitute points of support – or counterpoints – in the conception of the olfactory identities of cities.

The contemporary stakes of such a “spatial-olfactory” approach go far beyond issues relating to habitual anxieties concerning air quality with which smells are rightly or wrongly associated. For us today, it is more a question of how “readable” or comprehensible urban spaces are to inhabitants in their daily lives. How they contribute to the creation of a reassuring sense of place, appealing to all of our senses in order to the greatest possible definition to our common urban life.
 
 
 
 

Notes
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Suzel Balez is a Ph.D. architect, researcher at the Ambiances, Architectures, Urbanités research center (UMR CNRS 1536). She is currently a professor at the École Nationale Supérieure d’Architecture de Paris la Villette (ENSAPLV), teaching mainly environmental stakes and ambiances perception and design, especially regarding public spaces. Her research focuses on the aerial and more specifically olfactory forms of ordinary sensory experience. This sensory experience is now at the heart of her concerns, particularly regarding ecological transformations and more specifically in public spaces. She has just supported her accreditation to direct research on the olfactory apprehension in places (currently being published).

Volume 5, no. 2 Jun-Dec 2022