Huh?
There is no way you could have known that the other cars emissions were different, unless you have some kind of gas-analyzer built into your eyes there Mr. Cyclops LOL...

No seriously, it's because of the outside temperature and the humidity that some cars' emissions may "look" different. Indeed they are different, in the amounts of NOx and CO and CO2 being emitted, but it is because the car may have just been started and the exhaust system is still very cold. This will cause condensation to occur, making it look as if it is polluting more than other cars with hot exhaust systems.

It is totally normal, so no worry. Unless of course you have CEL's which are a totally different story. Could be a number of things, post your codes and we can help from there.