Southampton City Council's consultation on Clean Air Zone plans closed on the 13th September. Under the current proposals the CAZ would cover most of the city (see map below) though this will be refined if the proposal meets with approval.
The proposed charge per day for non-compliant HGVs is £100 with no charge currently proposed for non-compliant vans. However these charges are not final and may change before the target implementation date at the end of 2019.
The consultation document and comprehensive FAQs are available here.