Could Breath THC Be in Vapor as Well as Aerosol? What a Physical Model Shows

THC in exhaled breath may need to be considered in both vapor and particle-associated forms. A physical-chemistry study measured cannabinoid vapor pressures and used a model to predict gas–particle partitioning. It did not directly establish which phase dominates in every person’s breath or validate a breathalyzer for impairment.

What was measured directly

Beuning and colleagues measured vapor pressures of delta-9-THC, CBD and CBN using a gas-saturation approach. The experimental temperatures were 364 to 424 kelvin, substantially above ordinary exhaled-breath temperatures.

The measurements supply physical-property data relevant to how these compounds might distribute between air and aerosols. They are laboratory measurements of substances, not a clinical study involving cannabis users or a comparison with observed driving behavior.

What the breath model predicted

The researchers extrapolated the temperature-dependent measurements and modeled partitioning under conditions relevant to breath. Their analysis predicted a substantial, and under the modeled conditions predominant, vapor-phase contribution. Temperature and aerosol concentration were important to that prediction.

A prediction based on physical properties should be reported as a prediction. It is not a direct count of vapor-phase THC in fresh human breath. Extrapolation beyond the experimental temperature range and uncertainty in actual breath conditions affect how confidently the model can be applied.

Why collection design matters

A device designed to collect particles may not capture a vapor component in the same way. Conversely, finding THC on a filter does not resolve how much was originally present in each phase. A complete collection validation needs to address what the device captures, what it misses and how temperature changes during sampling.

This physical study therefore raises a measurement question rather than supplying a fixed detection window. A captured THC amount still needs separate evidence before it can be interpreted as recent use or impairment.

Our discussion of edible and vaporized cannabis timing addresses human exposure and performance. The physical model supplies a different piece of the evidence: understanding the form of the material being collected before drawing conclusions from its absence or presence.

Primary research

Vapor pressure measurements on Δ9-tetrahydrocannabinol, cannabidiol, and cannabinol to inform cannabis breathalyzer development. DOI: 10.1088/1752-7163/ae3794.