Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search), "50 nn decrease" (Expand Search), "50 pa decreased" (Expand Search), "5 ppm decrease" (Expand Search)
"5 nm decrease" » "5 nn decrease" (Expand Search), "5 _ decrease" (Expand Search), "5 we decrease" (Expand Search), "5 mm decrease" (Expand Search), "5 cm decrease" (Expand Search)
"5 a decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ decreases" (Expand Search)
"50 c decrease" » "50 c decreased" (Expand Search), "50 _ decrease" (Expand Search), "50 rc decreased" (Expand Search), "5 c decrease" (Expand Search), "50 μ decrease" (Expand Search)

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"50 ppm decrease\") OR (((((\"5 a decrease\") OR (\"50 c decrease\"))) OR (\"5 nm decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 5 a decrease ) OR ( 50 c decrease ))) OR ( 5 nm decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("5 a decrease") OR ("50 c decrease"))) OR ("5 nm decrease"))))*.