Check with your airline for the most accurate answer in terms of his being able to leave the transit area based on his ticket and regulations.
With only 8-hours, you may just want to consider this
http://en.bcia.com.c...ce/lounge.shtml (see pricing and booking here
http://en.bcia-shopp.../store/844.html)
Don't take me or anyone else's words about this unless they have just recently done it but ... As best I am aware a transit visa is not needed if he is from the US but a transit visa doesn't allow you to leave the airport and instead he would have to get what I believe is called a temporary landing permit and it may be available at some airports / cities in China and not others.
But again, 8-hours is not a lot of time to deal with the hassles of leaving and returning and their might even be issues with any checked bags and which the airline could also tell you about.