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 ng decrease" » "5 nn decrease" (Expand Search), "5 _ decrease" (Expand Search), "5 we decrease" (Expand Search), "5 mg decrease" (Expand Search), "5 g decrease" (Expand Search), "5 nm decrease" (Expand Search)
"50 a decrease" » "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 _ decreases" (Expand Search), "50 μ decrease" (Expand Search), "5 a decrease" (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 (\"50 a decrease\"))) OR (((\"50 c decrease\") OR (\"5 ng decrease\"))))~".
• Removing quotes may allow a broader search: (((( 50 ppm decrease ) OR ( 50 a decrease ))) OR ((( 50 c decrease ) OR ( 5 ng decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (((("50 ppm decrease") OR ("50 a decrease"))) OR ((("50 c decrease") OR ("5 ng decrease"))))*.