Perhaps you should try some spelling variations:
"5 ppm decrease" » "5 _ decrease" (Expand Search), "5 a decrease" (Expand Search), "5 nn decrease" (Expand Search)
"50 ng decrease" » "50 nn decrease" (Expand Search), "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 mg decrease" (Expand Search), "10 ng decrease" (Expand Search), "5 ng decrease" (Expand Search), "50 nsg decrease" (Expand Search), "50 μg decrease" (Expand Search), "50 _g decrease" (Expand Search)
"50 n decrease" » "50 nn decrease" (Expand Search), "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 ns 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: "((\"5 ppm decrease\") OR (((\"50 n decrease\") OR (\"50 ng decrease\"))))~".
• Removing quotes may allow a broader search: (( 5 ppm decrease ) OR ((( 50 n decrease ) OR ( 50 ng decrease ))))~.
• Adding a wildcard symbol may retrieve word variants: (("5 ppm decrease") OR ((("50 n decrease") OR ("50 ng decrease"))))*.