First things first, make sure that you are setup as the online chairperson for your event. There are certain permissions that you need to be granted on the website before you can send mass emails and regular participants can't access the menu that you need.

Once you've verified that you have those permissions (if you don't, talk to your ACS staff member), log in to your website and click on "event management." There is an email section within the event management screen and you can select whatever groups that you want.. including past participants broken down by year.

As online chairperson, you should have gotten a binder or a packet of information that walks you through the email process and other important functions. Without the administrator access to the site, however, that information won't help much. ;-)

Hope that helps! When all else fails, ask your ACS staff member. They are a wonderful resource.

Good luck!