Marijuana odor perception: studies modeled from probable cause cases.

The 4th Amendment of the United States Constitution protects American citizens against unreasonable search and seizure without probable cause. Although law enforcement officials routinely rely solely on the sense of smell to justify probable cause when entering vehicles and dwellings to search for illicit drugs, the accuracy of their perception in this regard has rarely been questioned and, to our knowledge, never tested. In this paper, we present data from two empirical studies based upon actual legal cases in which the odor of marijuana was used as probable cause for search. In the first, we simulated a situation in which, during a routine traffic stop, the odor of packaged marijuana located in the trunk of an automobile was said to be detected through the driver's window. In the second, we investigated a report that marijuana odor was discernable from a considerable distance from the chimney effluence of diesel exhaust emanating from an illicit California grow room. Our findings suggest that the odor of marijuana was not reliably discernable by persons with an excellent sense of smell in either case. These studies are the first to examine the ability of humans to detect marijuana in simulated real-life situations encountered by law enforcement officials, and are particularly relevant to the issue of probable cause.

Comparison of detection threshold values determined using glass sniff bottles and plastic squeeze bottles.

Olfactory threshold measures are influenced by such factors as odorant species, diluent type, psychophysical paradigm, and stimulus-presentation procedure. In this study, we compared phenyl ethyl alcohol odor-detection thresholds obtained using 120-ml glass sniff bottles to those obtained using 120-ml plastic squeeze bottles. Although these presentation media are commonly employed in published studies, there has never been a formal comparison of values obtained using them. 10 male and 10 female subjects were tested on two threshold test sessions, one for each type of bottle. Order of sessions was systematically counterbalanced and completed on the same day for a given subject, with a minimum of 30 min. elapsing between sessions. A seven-reversal, single-staircase threshold procedure was employed. Although the threshold values were similar for the two procedures, slightly lower thresholds were obtained using the glass sniff bottles [respective M (SEM) log vol/vol values = -6.61 (.20) and -6.13 (.24)]. These data suggest that, while threshold values using these two presentation procedures can be roughly compared across studies, accurate comparisons may require a slight mathematical adjustment.