Perhaps you should try some spelling variations:
dioxin emissions » dioxide emission, down emissions, toxic emissions
focal emissions » vocal emissions, coal emissions, vocal emission
voc emissions » bvoc emissions, voc emission, vocal emissions

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 (focal emissions)) ) OR ( ((dioxin emissions) OR (dioxide emissions)) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( ((voc emissions) or (focal emissions)) ) or ( ((dioxin emissions) OR (dioxide emissions)) ))".
• Adding a wildcard symbol may retrieve word variants: (( ((voc emissions) or (focal emissions)) ) or ( ((dioxin emissions) OR (dioxide emissions)) ))*.