I searched through my “Perry’s” which was the chemical engineer’s bible in my day. A close organic compound to your anise oil in terms of boiling point was nicotine. Nicotine boils at 247C and anise oil boils at 238C (460F). The vapor pressure/temperature profile for nicotine follows as (vapor pressure in mmHg/temp degrees C): 1/62, 5/92, 10/107, 20/124, 40/142, 60/155, 100/170, 200/194, 400/220, 760/247. Normal graph paper is useless for plotting this for your temperature range so I would try semi-log paper which I do not have. Maybe you could extrapolate down to your temperature region to guess at the change in vapor pressure between 77F (25C) and 32F (0C).
I also looked at organic compounds that had vapor pressure data for your temperature range; that is, from 25C down to 0C. Here is that data:
Degrees C Degrees C Degrees C
V.P. mmHg N-nonane N-butyl Pentachloro-
Ketone ethane
1 1.4 -1.4 1.0
5 25.8 19.7 27.2
It appears that many organic compounds undergo a 5-fold drop in vapor pressure between 25C and zero C. If I were working your problem I might conclude I had to increase the concentration of anise oil 5-fold to get the same vapor pressure at zero C as at 25C.
I sure am glad I no longer have to earn my living by my expertise in chemistry and vapor pressures. Good luck.
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