Air, which sorts and carries packages for DHL, says it plans to lay off an additional 1,000 workers at its operation in western Ohio by the end of August, reducing the air carrier’s presence there to about 1,300 employees. ABX and other businesses at the Wilmington Air Park have been laying off workers since DHL Express announced in May 2008 it was pulling out. About 8,000 workers were employed at the air park then.