Final answer:
Skunk spray can be detected by humans at concentrations less than 10 ppb. Some animals, like moths, have a remarkable sensitivity to certain odors and can detect them from several miles away. Individual sensitivity to skunk spray may vary.
Step-by-step explanation:
The distance at which skunk spray can be detected by humans depends on various factors, such as wind direction and concentration of the spray. However, it has been estimated that skunk spray can be detected by humans at concentrations less than 10 parts per billion (ppb). This means that even at very low levels, skunk spray can be smelled by humans.
For comparison, it has been observed that some moths can detect certain odors from female moths over distances of many miles, such as 4,000 meters, if there is a gentle breeze blowing in the right direction. This demonstrates the remarkable sensitivity of certain animals' olfactory systems.
It's important to note that individual sensitivity to odors may vary, and some people may be more sensitive to skunk spray than others.