ANCHORAGE, Alaska (AP) — Two Royal Dutch Shell PLC ships operating in the Arctic emitted excessive amounts of air pollution during drilling operations last summer off Alaska’s northern coastline, according to the Environmental Protection Agency.

The federal agency announced Thursday that it issued Shell notices of air quality violations coming from its drill rig and drill ship during what was a shortened Arctic drilling season of about two months. Shell’s drill rig Kulluk and drill ship Noble Discoverer emitted excessive amounts of nitrogen oxide. There were multiple violations for each ship, the agency said.