The European Union's environmental agency says air pollution is slowly improving across the continent but still exceeds the bloc's limits and guidelines from the U.N. health agency.

The European Environment Agency on Monday issued its 2018 report on air quality and said emissions from road traffic, agriculture, energy production, industry and households are churning out pollutants like particulate matter, nitrogen dioxide and ground-level ozone.

Agency head Hans Bruyninckx said: "Air pollution is an invisible killer and we need to step up our efforts to address the causes."

He said Europe must "redouble its efforts to reduce emissions caused by transport, energy and agriculture and invest in making them cleaner and more sustainable."

The report was based on more than 2,500 monitoring stations across Europe in 2016, the latest available data.