When I wrote the
achemso class for submissions to American Chemical Society journals, I did my best to get the style of each journal correct. Of course, this is not easy as there are a lot of journals and they are not necessarily consistent in applying the style rules! One issue that comes up a lot is section numbering. Most of the journals do not number sections, most of the time. However, sometimes authors want to include section numbers. I need to look at this again for version 3.2, but in version 3.1 you need to do:
\makeatletter \acs@restsecnums \makeatother
somewhere in the preamble to restore numbering.