Complex sentence: The 2008 Euro V European emission standards set a limit on carbon monoxide from heavy-duty diesel engines of 1.5 g/kWh, which is one third that of the 1992 Euro I standard.
Split into simpler sentences: The 2008 Euro V European emission standards set a limit on carbon monoxide from heavy-duty diesel engines of 1.5 g/kWh. This is one third that of the 1992 Euro I standard.