Perhaps you should try some spelling variations:
ppm decrease » a decrease (Expand Search), pa decreased (Expand Search), 026 decrease (Expand Search)
nn decrease » a decrease (Expand Search), mean decrease (Expand Search), gy decreased (Expand Search)
c decrease » c decreased (Expand Search), a decrease (Expand Search), rc decreased (Expand Search)
_ decrease » _ decreased (Expand Search)
50 ppm » 5 ppm (Expand Search)
50 c » 5 c (Expand Search), 50 μ (Expand Search), 50 _ (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 ( 50 c decrease ))) OR ( 50 ((nn decrease) OR (_ decrease)) ))~".
• Adding a wildcard symbol may retrieve word variants: (((( 50 ppm decrease ) OR ( 50 c decrease ))) OR ( 50 ((nn decrease) OR (_ decrease)) ))*.