Need events to expire in a custom WP Loop

I am using a carousel on my front page to display current events and I’m trying to use a WP Loop, I need the filter by event date so that old events won’t show up in the carousel.

http://mcofest.org/

I wanted to use the meta_key and meta_compare parameters, I just need to know what the key is.

I’m trying to use something like this:

<?php
                $today = date("Ymd")-1;
                $args = array(
                    'post_type' => 'ai1ec_event'
                    'showposts' => -1,
                    'suppress_filters' => true,
                    'meta_key'  => '???' ,
                    'meta_compare'  => '>=' ,
                    'meta_value'  => $today,
                    'orderby'  => 'meta_value',
                    'order'  => 'ASC'
                );
                query_posts( $args );?>
. . .

I did a query on meta keys and I wasn’t able to pull up any for the event date but it must come from somewhere?

http://wordpress.org/extend/plugins/all-in-one-event-calendar/