Eliminating any turbulent effects, you would need to calculate the molar mass of the two compounds that creates the smell. Then by simply applying Graham’s law,
\(\large \frac{Diffusion \ Rate \ 1}{Diffusion \ Rate \ 2} = \large \sqrt {\frac {Molar \ Mass \ 2}{Molar \ Mass \ 1}}\)
you can find which the faster smell is. Still, it won’t be that accurate.
Also, if you are so curious, you can analyze the diffusion co-efficient using the formula from the wiki I linked above.
