Carbon emissions at sea have received more attention over the last decade. Ports, especially, can have a negative impact on air quality in the populated areas that surround them. The many emissions sources at ports include ships, trucks, trains, and cargo-handling equipment. Harbor-crafts also contribute a significant portion of total port emissions. These include tugboats, ferries, fishing boats, and dredge vessels. Recently, the Ports of Los Angeles and Long Beach have started using a hybrid electric tugboat. A new study by the University of California (UC) Riverside has shown that this has been effective at reducing emissions.