Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 a 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 a decrease" (Expand Search), "5 we decrease" (Expand Search), "5 mg decrease" (Expand Search), "5 g decrease" (Expand Search), "5 nm decrease" (Expand Search)
"50 n decrease" » "50 nn decrease" (Expand Search), "50 a decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 ns decrease" (Expand Search), "50 ng 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 n decrease\") OR (\"50 _ decrease\"))) OR (\"5 ng decrease\"))))~".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((((( 50 n decrease ) OR ( 50 _ decrease ))) OR ( 5 ng decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("50 ppm decrease") OR ((((("50 n decrease") OR ("50 _ decrease"))) OR ("5 ng decrease"))))*.