There is also a direct a/c bus from Beijing to the Tianjin Airport, without going through TJ city. It leaves from Dawang Lu (Bawangfen long distance bus station, not too far south of Jianguomen, near the river). But it only operates during the daytime, is not incredibly frequent, and probably still takes 2 hours..though I think it's pretty cheap and the bus quality is good. This bus also runs in the opposite direction, from TSN to Beijing Bawangfen. Might be an option to/from those heading for Beijing SE part of city and CBD.

TSN is also an international airport and can sometimes be a useful backdoor if PEK flights are full or priced sky-high, though you'll likely need to route via NRT or ICN.