Here in Missouri they used to have a hose that went into the tailpipe while the engine was running, this measured all of the emissions going out of the exhaust. It was given the nick name tailpipe sniffer
yes, here in the uk cars have to have a tailpipe emissions test every year as part of the 'mot' (roadworthyness/safety) test. the level of acceptable emissions gets lower as the vehicles get newer so pretty standard stuff i guess.
neil.