One of the greatest travesties I think in nose work is the term “scent cone”. Why? Because it’s not a “cone” at all! It’s a PLUME! As a result of this unfortunate visual, nosework handlers all over the world picture an ice cream cone or a traffic cone when trying to visualize odor. This may be seen of no consequence, however it distinctly affects our understanding of odor movement and in the end, our capabilities as nosework handlers. If we can understand scent as a PLUME, we will be in much better shape when trying to picture scent movement.
Smoke plumes mimic odor movement and are a closer representation
Why not an Ice Cream Cone?
This is your typical visualization of a scent cone:
This is a common way to visualize a Scent Cone. Although directionally correct, it is simplistic and only somewhat accurate
The typical thought process in the sport of Nose work is to think of odor as “cones” of odor. This is highly simplistic and only a little true. It neglects the aspects of buoyancy, temperature differentials, gravity, air momentum and directionality. All of these forces act on the odor, and the result is the shape of the actual “scent cone” and scent cone behavior. If you can understand these forces you will be in a much better position to read your dog.
Scent cones actually come in innumerable shapes, and the size of the scent cone is determined by the wind speed and the length of time the source odor has been available (wind speed and aging). Ultimately, the shape of the scent cone comes down to air flow and the density of the scent particles compared to air. Scent particles are heavier than air but are still light enough to be easily carried on air currents, especially when we are targeting essential oils! Essential oils are extremely volatile, meaning that the air particles escape easily into the air.
Meet the REAL Scent Cone
The REAL Scent Cone is a plume. It’s wispy in nature and changes directions seemingly randomly at times. Have you ever stood in the wind and realized that wind direction and speed shifts constantly? Well so does a scent cone! This is one reason why one dog may come into a room and quickly find a hide where the next dog may “miss” catching the scent cone. To some extent the dog has to be in the right place at the right time. This means that hunting for the scent cone is a critical skill of the detection dog. Scent cones are NOT static and they DO move and shift.
The basic shape of the scent cone is dictated primarily by air movement. Air movement is driven by the Ideal Gas Laws which describe the relationship between pressure, volume and temperature. Essentially, you need to know two things. First of all, air will move from an area of high pressure to an area of low pressure (picture squeezing a balloon). Secondly, hot air rises and cool air sinks. These are the two primary forces driving air movement, both indoors and out!
A dry ice plume gives us a decent (although still not entirely accurate) visual of a scent plume. Keep in mind that the dry ice vapor will be colder than the air temperature, and the plume will therefore fall in relation to the air. However, it helps us to understand the volatile wispy nature of the scent cone.
What about Buoyancy and Temperature?
The rise or fall of a scent cone is affected by two things… (1) buyoancy and (2) temperature differentials. Temperature differentials make air rise or fall. Air in warmer areas such as in the sun, rise, causing more air to backfill the volume left by the rising air. Then when the air encounters cooler temperatures such as in the shade, the air falls. Scent cones will ride the temperature differentials causing the scent profile to change. An example of this is air flowing in a convection current.
An example of a Convection Current. A Scent cone from a hide on the window would lift and fall on the other side of the room.
Buoyancy is affected by temperature and density to a great degree. Because target odor is at the same temperature as the surrounding environment, temperature is taken out of the equation. Therefore, lift (or fall) of odor depends on density and something called reduced gravity. Essentially odor is heavier than air, therefore it will fall at a slow rate. When you combine this with air flow, you determine the scent cone shape.
For example, with a high hide, the tendency of the shape of the scent cone will be to fall gradually. This affects how we search for high hides and explains why the dog may need to be farther away from source in order to solve the puzzle rather than close in.
When a scent cone develops from an elevated hide, the scent drops slowly at an angle to the ground.
Overall, learning the true shape of a scent cone will make a handler more powerful by providing a new perspective on visualizing scent movement.
Learning More
This term, I’m teaching an online class that covers helping your dog to understand multiple overlapping scent cones, or rather Converging Odor. NW241 Nosework Challenges Series 2 is available at Fenzi Dog Sports Academy.
This is the BEST explanation of air/scent movement ! Everyone who does NW should read this! Maybe we should change the term “Scent cone” to “Scent Plume”…..
Scent cone is a term associated more commonly with live find SAR using a very large odor source with directional wind. If it has become common language in scent sports, that’s too bad since, as you point out, it is not a cone. I use odor pool, plume as also a good term. I hope instructors are educating themselves on scent theory so they can be passing this knowledge to their students. Dog’s arent magic..they have the very difficult job of acquiring odor and then trying to interpret and follow, some times tendrils, of odor back to source.
Hi Jen… I completely agree… I’m assuming you do Live Find SAR? You’ll find in scent sports that the term “Scent Cone” is common vernacular. And I think understanding of scent theory is variable. This variability of one of the many reasons why I wrote this blog.
The term scent cone is use to describe where in police work , while doing a Track or Area Scout that the item or human subject that is being Tracked, or one where the item human subject is contained, with the help of wind direction depending on time and wind speed, working into the wind you can see where the dog pocks up the odor narrows their search pattern and follows to source. The same thing when searching for Narcotics and or explosives. With cadaver same rules applie unless they are buried or under water, dept age if it is whole or particial, many factors play into the scet be it indoors or out. The cone has been used to describe scent flow forever, it much easier to explain when instructing, back in the day you wsed a lit cigerite to demonstrate odor and it movement determined with the air.
Thank you Richard… yes, the term “Scent Cone” has been around forever… it’s just unfortunate for scent sports that the word “cone” is pretty inaccurate when it comes down to the actual shape of the odor. This article was written in order to bring light to the actual shape as that seems to be a great source of confusion for a great number of competitors, especially those that are new to the sport 🙂
Good terminology
Reminds me a lot of the chaos theory in physics. Great explanation, very helpful.
You say odor is heavier than air, therefore it will fall at a slow rate. Shouldn’t something heavier fall faster?
It WILL fall however because it’s also very light, it will fall slowly (susceptible to upward air drafts)… picture a feather falling rather than a stone. A stone will fall quickly while a feather will float down. You can also picture odor as fat snowflakes… again, heavier than air but still susceptible to upward air drafts. Does that make sense?
Makes perfect sense. Best article I’ve read on scentwork. Thanks.
Good write, I like that.
As a tracking judge I have seen this work all the time. This is important information for all tracking judges to learn and understand. In Urban tracking knowing what the scent will do if extremely important to plot good tracks and for handlers to understand where the scent is while handling their dogs in training and a test. Great article.