Perhaps you should try some spelling variations:
photon emissions » photon emission, phonon emission, photo emission
down emissions » von emissions, dioxin emissions
voc emissions » bvoc emissions, vocal emissions, bvocs emissions
voc emission » ion emission, vocal emissions, 7 emission

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( ((voc emissions) OR (voc emission)) ) OR ( ((down emissions) OR (photon emissions)) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( ((voc emissions) or (voc emission)) ) or ( ((down emissions) OR (photon emissions)) ))".
• Adding a wildcard symbol may retrieve word variants: (( ((voc emissions) or (voc emission)) ) or ( ((down emissions) OR (photon emissions)) ))*.