As someone who lives next to the port of Oakland, allow me to say that ships are indeed an issue in urban environments, and they do cause large amounts of pollution. And besides the ships, there are usually a number of diesel trucks that are coming to ship goods to and from the port.

Recent state and federal regulations have made this less a problem.

Have you ever been to Long Beach CA? Take a look at the (frequently) dozens of containter and tanker ships idling just offshore. Any major port city will have the same issue, transport ships waiting, for various reasons, just outside of a port with their engines running. Any refrigerated cargo needs to be cools, which requires power, which means that they run 24x7 while sitting around.

there was a push to improve shore-power options for these ships a while back, but i'm not sure where it went. probably deemed to costly or intrusive by the shippers.