Earlier quoted context omitted.
Note that, for emmesions, heating up the car in stationary is actually positive. It prevents driving a car with a cold engine. Cold engines cause horrible inefficiency in cars. It's one of the reasons why city driving is worse for mileage and emissions than highway driving. Shorter trips.
I am unable to find a source for this. Until now I thought heating up stationary is bad concerning all possible aspects, including emissions.
“Vehicles fitted with catalytic converters emit most of their total pollution during the first five minutes of engine operation; for example, before the catalytic converter has warmed up sufficiently to be fully effective.”