Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search)
"50 c decrease" » "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 _ decreases" (Expand Search), "50 i decrease" (Expand Search)
"50 a decrease" » "50 _ decrease" (Expand Search), "50 _ decreased" (Expand Search), "50 _ decreases" (Expand Search), "50 i decrease" (Expand Search)
"5 a decrease" » "5 _ decrease" (Expand Search), "5 _ decreased" (Expand Search), "5 _ decreases" (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 c decrease\") OR (((\"50 a decrease\") OR (\"5 a decrease\"))))) OR (\"50 ppm decrease\"))~".
• Removing quotes may allow a broader search: (((( 50 c decrease ) OR ((( 50 a decrease ) OR ( 5 a decrease ))))) OR ( 50 ppm decrease ))~.
• Adding a wildcard symbol may retrieve word variants: (((("50 c decrease") OR ((("50 a decrease") OR ("5 a decrease"))))) OR ("50 ppm decrease"))*.