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" » "5 _ decrease" (Expand Search), "5 a decrease" (Expand Search), "5 pa decreased" (Expand Search)
"50 nn decrease" » "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 mean decrease" (Expand Search), "50 ns decrease" (Expand Search), "50 ng decrease" (Expand Search), "50 n decrease" (Expand Search)
"50 c decrease" » "50 c decreased" (Expand Search), "50 _ decrease" (Expand Search), "50 a decrease" (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.

• Performing a fuzzy search may retrieve terms with similar spellings: (((((("50 ppm decrease") OR ("50 c decrease"))) OR ("5 ppm decrease"))) OR ("50 nn decrease"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((\"50 ppm decrease\") OR (\"50 c decrease\"))) OR (\"5 ppm decrease\"))) OR (\"50 nn decrease\"))*".
• Removing quotes may allow a broader search: (((((( 50 ppm decrease ) OR ( 50 c decrease ))) OR ( 5 ppm decrease ))) OR ( 50 nn decrease ))*.