The City with No Smells

We all know that air pollution is a real threat, both to ourselves and our planet. And we all know that automobiles and electricity generated by fossil fuels are the major contributors to this pollution, and mostly because they are visible (except that they’re really not visible – the plumes you see exhausting from tailpipes and smokestacks tend to be water vapor; the polluting parts are invisibly microscopic.)

But there's another suspect out there which goes largely ignored, and as it would, because it's largely invisible to us.

We're not talking about cow farts, but cooking grease. To be more scientific, it is called organic aerosols, and it comes from the oils and organic matter that are heated in the process of cooking, and ejected out of the kitchen and into our urban environments.

As science starts to zero-in on atmospheric offenders, the local sources of pollution become more apparent. You will be way more exposed to the particulate matter exhausting from a tailpipe if you're driving right behind one, as opposed to watching it from your apartment window. But you are also more exposed to the organic aerosols exhausted from your local taqueria as you walk around your neighborhood, as compared to a pollution meter stationed on the roof of your 4-story apartment building.

So although global pollution is a problem for sure, local pollution is a problem even moreso, and one that needs to be managed in order to raise the quality of life for ever-increasing urban populations.

Thing is, although organic aerosols may be invisible, they are smellable. And although there are plenty of examples of restaurants "polluting" our urban environment with rancid reminders of why Yelp is still in business, there are just as many examples of locale-defining odor profiles marking your travels about your home neighborhood, or your favorite tourist destination.

Popcorn at the movie theater* is an obvious example, but there are plenty more of these olfactory advertisements to enjoy, and which even help to define a neighborhood. It's interesting to think of a historic preservation society that adds to their list of cornices and cobblestones a particular plume that really defines a place – a specific combination of cultural cuisine that can only be found in that little nook where the Polish krautmakers and Indian currystirrers all live together.

That being said, it’s not hard to imagine a future where everything that smells is bad for you and hence ridden. A city with no smells. Very healthy, very uninspiring.

*I was recently informed by a friend that, to him, "popcorn smells like vomit," which does make sense IF the butter is rancid, because isovaleric acid is a primary constituent of rancid butter, and is the smell of vomit and fermented feet sweat.

Notes:

Eating out, breathing in

Nov 2018, phys.org

Post Script:

Good smells aside, when you roast things like nuts, popcorn or coffee, some of the compounds released are called diacetyls, which can cause serious respiratory problems for workers exposed to it in high amount.

Image source – link

The Japanese Aesthetic

 Reading a bit about urban planning lately, and this one comes up a lot:

Around the year 2000, Japan’s Ministry of the Environment decided to establish protection for 100 sites around their country because they smell good. Yup – here in the US, we’re having trouble protecting our own damn water supply, and Japan is thinking about their national smellscape. I’ve read about this more than once now, but an internet search makes it seem like it’s not real.

And I keep coming across the same passage:

…sea mist of Kushiro to the Nanbu rice cracker of Morioka, not to mention the distinct smell of glue that hangs in the air around the doll craftsmen’s homes in Koriyama, all now have protected status...

-seems to have been written by Victoria Henshaw in her book Urban Smellscapes, 2013.

But here’s another one:

…vegetation (‘a hundred thousand peach blossoms at a glance’), food (‘rice cracker of Morioka’), and urban odours (‘streets of used bookstores’)

And since we’re talking about Japan, we can’t forget that really important thing about how smell is regarded differently across cultures. In Japan, and other Eastern countries, fragrance is not something that you wear on your body, but something that is in the environment around you. Maybe, or probably, this has something to do with the fact that the Japanese, and other Asian cultures, have no body odor. If you don’t believe me, you might want to ride the subway in Tokyo during rush hour.

Local Odor Vocab

Curren's SCAQMD Urban Odor Dictionary

link to google fusion graph

You’re looking at a smell network based on the work of UCLA post-grad named Jane Curren. She took all the words used in odor complaints in southern California, and found the source of those complaints. These odor sources can be anything from a hidden garbage dump to a local restaurant. The size of the blue nodes doesn’t indicate smelliness; it indicates more descriptors. Restaurants have more descriptors because they have 1. More people near them and 2. A greater diversity of things that smell. (I’m guessing this.) What this chart does show is the most common odor complaints in the middle of the cluster – we smell burnt things a lot. Also rotten eggs/sulfur/natural gas.

Below, Curren went further and found the specific chemical source of these smells, and I listed them below. Next time you smell something funny, check this list. (And the next time you’re in New Jersey, take a tour of the New Jersey Turnpike mobile museum of olfactory delights, you’ll smell firsthand many of the odors on this list!)

Curren's Urban Odor Lexicon

               

Descriptor                           Odorant

solvent                                 2-butanone

petroleum                          2-methyl-1-propene

pungent                               2-pentanone

sweet                                   2-pentanone

lemon                                   acetaldehyde

alcohol                                  acetaldehyde

acrid                                      acrolein

pungent                               ammonia

sweet solvent                   benzene

sweet                                   dichloromethane

decayed cabbage             ethyl mercaptan

pungent                               formaldehyde

rotten egg                           hydrogen sulfide

woody                                  m-cresol

resinous                               m-cresol

medical                                                m-cresol

woody                                  o-cresol

resinous                               o-cresol

medical                                                o-cresol

woody                                  p-cresol

resinous                               p-cresol

medical                                                p-cresol

medical                                                phenol

sweet                                   phenol

irritating                               propanal

fruity                                     propanal

empyreumatic                  pyridinec

irritating                               sulfurdioxide

aromatic                              toluenec

fishy                                      trimethylamine

pungent                               trimethylamine

sweet                                   acetone

minty                                    acetone

sweet solvent                   benzene

woody                                  cresol

resinous                               cresol

medicinal                             cresol

sour                                       dimethyl disulfide

onion                                    dimethyl disulfide

decayed cabbage             dimethyl sulfide

decayed cabbage             ethyl mercaptan

garlic                                      ethyl mercaptan

aromatic                              ethylbenzene

pungent                               formaldehyde

rotten eggs                         hydrogen sulfide

skunk                                    i-propyl mercaptan

sour                                       methyl mercaptan

garlic                                      methyl mercaptan

decayed cabbage             methyl mercaptan

skunk                                    n-butyl mercaptan

skunk                                    n-propyl mercaptan

medicinal                             phenol

sweet                                   phenol

irritating                               propanal

sweet                                   p-xylene

sharp                                     thiophene

skunk                                    thiophene

rubber                                  toluene

moth balls                           toluene

aromatic                              1,2,4-trimethylbenzene

aromatic                              1,3,5-trimethylbenzene

vinegar                                 acetic acid

sour                                       acetic acid

chemical                              acetone

sweet                                   acetone

acrid                                      acrolien

pungent                               ammonia

sweet                                   a-pinene

pine                                       a-pinene

sweet solvent                   benzene

malty                                     butanal

burnt                                     butanal

rancid                                    butyric acid

sour                                       butyric acid

perspiration                       butyric acid

fruity                                     butyl acetate

dead body                          cadaverine

disagreeable sweet        carbon disulfide

almond                                 chlorobenzene

sweet                                   chloroform

ethereal                               chloroform

pungent                               crotonaledehyde

gasoline                               decane

ethereal                               dichloromethane

sour                                       dimethyl disulfide

onion                                    dimethyl disulfide

decaying vegetation       dimethyl sulfide

aromatic                              ethylbenzene

oily                                         heptanal

musty                                   heptanal

woody                                  heptanal

fatty                                      hexanal

green                                    hexanal

rotten egg                           hydrogen sulfide

sharp                                     isopropyl benzene

aromatic                              isopropyl benzene

sharp                                     cumene

aromatic                              cumene

lemon                                   limonene

decayed cabbage             methyl mercaptan

moth balls                           naphthalene

tar                                          naphthalene

sweet                                   m-xylene

gasoline                               octane

sweet                                   o-xylene

pungent                               pentanal

sharp                                     propanal

vinegar                                 propanoic acid

sour                                       propanoic acid

sweet                                   p-xylene

solvent                                 styrene

rubber                                  styrene

sweet                                   tetrachloroethene

rubber                                  toluene

moth balls                           toluene

sweet                                   tricholoroethane

fishy                                      trimethylamine

fecal                                      valeric acid

sour                                       valeric acid

sweet                                   vinyl acetate

Suffet and Rosenfeld's Urban Odor Lexicon

*much of Curren’s work came from Suffet and Rosenfeld, so I added their leftover terms here

Descriptor                           Odorant

Coffee                                  Furfruryl Thiopropionate

earthy                                   Geosmin

musty                                   2-Methyl isoborneol

moldy                                   2,4,6-Trichloroanisole

grassy                                   Cis-3-hexen-1-ol

dead animal                       Putresine

rotten vegetable              Dimethyl Trisulfide

fishy                                      Dimethyl Amine

fishy                                      Methyl Amine

plastic                                   Methyl Methacrylate

fecal                                      Indole

manure                                  Skatole

burnt                                     Guiaicol

Primary document: Curren, J. 2012. Characterization of Odor Nuisance. UCLA.

http://www.wcsawma.org/wp-content/uploads/2012/11/JMC-dissertation.pdf

Supporting document: Suffet, I.H., and P.E. Rosenfeld (2007). The Anatomy of Odour Wheels for Odors of Drinking Water, Wastewater, Compost and the Urban Environment, Water Science and Technology 55(5), 335-344.

Research note: The descriptor names come from the above source and supporting documents, whereas the odor causing compounds were matched against varying sources which will not be listed here; see instead the source document for those references

Constructing an Urban Smell Map

Must be something in the air. Over the past few years, many artists/scientists have been making smell maps of their cities. Victoria Henshaw is the most popular, with her “smellwalks” and her book Urban Smellscapes. But there’s others, like Kate McLean’s Sensory Maps, and Jason Logan’s handscrawled Scents and the City (seen above).

I think it’s just that maps are becoming a big deal. Something about big data, social media, and GIS interface. Maybe that Snapchat debacle too. The smell map we’re looking at today wraps up all three of these, and makes a very ambitious project into a neat interactive plaything. I wasn’t satisfied with the map, however, and was way more interested in the Urban Smell Dictionary they created in order to make their map I the first place. I was suspicious, so I went through their full report.

So here goes:

First they conducted smellwalks in each of the cities to be mapped (London and Barcelona), and along with some previous literature on the subject, they used the words generated on these smellwalks to support their lexicon. Then they collected geo-referenced picture tags from Flickr (530K), Instagram (35K), and Twitter (113K). Those tags and tweets were matched with the words in the smell dictionary, and voila!

The lexicon, in detail:

First they did some co-occurrence modeling, so that smell-words that appear in the same post/tweet are related. Then they used network analysis software, also called a community structure detection algorithm. InfoMap is the one they used, but they did further partitioning with another program.

The result?

Urban Smellscape Aroma Wheel

Who did it?

University of Turin computer science professor Rossano Schifanella, and Bell Labs researchers Luca Maria Aiello and Daniele Quercia.

Image source: “I Smell NY” Smell Map by Jason Logan

Notes:

Quercia, Daniele, Rossano Schifanella, Luca Maria Aiello, and Kate McLean. 2015. “Smelly Maps: The Digital Life of Urban Smellscapes.” In Proceedings of the Ninth International AAAI Conference on Web and Social Media (ICWSM 2015). Palo Alto, CA: AAAI Publications. 327-336. Accessed November 28, 2016.

http://www.aaai.org/ocs/index.php/ICWSM/ICWSM15/paper/view/10572

Full pdf:

https://www.aaai.org/ocs/index.php/ICWSM/ICWSM15/paper/view/10572/10516

Post Script:

There was a really cool observation made during their report which I’d like to explain here. In the remarks they make about “base notes,” there's some good entropy data in there somewhere, about smells, awareness, and the amount of time you spend in a place/some measure of odor-attenuation.

Let's start with their explanation of "notes" (and I’ll just quote from the paper)

“When a new perfume is created, different top, middle, and base note ingredients are combined to make the new fragrance. Those notes differ in terms of their tenacity. Top notes are those perceived immediately (e.g., citrus fruits, aromatic herbs) and, since they are intense, they are also volatile and evaporate quickly. By contrast, base notes are those adding depth and stay on the skin for hours (e.g., wood, moss, amber, and vanilla). Middle notes sit somewhere in between (e.g., flowers, spices, berries).”

Now they explain the urban smellscape:

“Base notes. The macro-level base notes for the urban smellscape are those that are likely smelled by a city’s first-timer visitors. That is because known odors are unconsciously processed by people, while only unfamiliar or strong odors are brought to people’s attention (as potential threats or sources of pleasure). As a result, residents are not likely to pay attention to their city’s base notes, while visitors would be able to consciously process them.

“Mid-level notes. As one moves through the city, the base notes blend with dominant smells that are localized in specific areas (e.g., factories, fish markets).

“High notes. Finally, the micro-level high notes are shortlived odors (e.g., goods from a leather shop). These are emitted in points that are very localized in space and time. … High notes are likely to go undetected because of data sparsity and because of our spatial unit of analysis being a street segment.”

And one more thing, I’m like how do you say this and not cite it??

 “Air pollutants also have been found to reduce the ability of floral scent trails to travel through air.”

-I’ve never heard this, and they provide no citation