Perhaps you should try some spelling variations:
"dioxide emission" » "dioxide emissions", "oxide emissions"
"voc emissions" » "bvoc emissions", "voc emission", "bvocs emissions"
"vocal emissions" » "local emissions", "focal 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 ("vocal emissions"))) OR ("dioxide emission")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"voc emissions\") OR (\"vocal emissions\"))) or (\"dioxide emission\"))".
• Removing quotes may allow a broader search: (((( voc emissions ) OR ( vocal emissions ))) or ( dioxide emission )).
• Adding a wildcard symbol may retrieve word variants: (((("voc emissions") OR ("vocal emissions"))) or ("dioxide emission"))*.