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