Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 pa decreased" (Expand Search), "5 ppm decrease" (Expand Search)
"50 nn decrease" » "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 mean decrease" (Expand Search), "50 n_ decrease" (Expand Search), "50 na decrease" (Expand Search), "50 n_ decreased" (Expand Search), "50 ns decrease" (Expand Search), "50 ng decrease" (Expand Search), "59 nn decrease" (Expand Search), "50 nsn decrease" (Expand Search), "50 ngn decrease" (Expand Search), "50 μn decrease" (Expand Search)
"50 n decrease" » "50 _ 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.

• Performing a fuzzy search may retrieve terms with similar spellings: (("50 ppm decrease") OR ((("50 n decrease") OR ("50 nn decrease"))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"50 ppm decrease\") OR (((\"50 n decrease\") OR (\"50 nn decrease\"))))*".
• Removing quotes may allow a broader search: (( 50 ppm decrease ) OR ((( 50 n decrease ) OR ( 50 nn decrease ))))*.