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