Getting rid of odors in the men's washrooms

I feel kinda silly for asking this, as I'm probably missing something obvious....I light-duty clean an office building where most employees are male. The men's washrooms have a urine odor every day, though they are cleaned daily. When I have extra time, I try to do things I'm not normally expected to do on a daily basis - washing walls and baseboards, eg. - and I apply an acid based bowl cleaner when scale builds up in the urinals.

All that being said, why the perma-stench and how can I take measures to eliminate it?

UPDATE: Thanks to everyone who commented! At the recommendations of most commenters, I went and used a locally manufactured enzyme-based solution last evening. Checking in today, the odors are significantly reduced or almost gone! Very pleased indeed