| Clue | Source | Date |
|---|---|---|
| Pollutant in engine exhaust | Newsday | 08 Dec 2018 |
| Explosive information: made energy absorbing one cow's smelly gas | The Telegraph Toughie | 13 Mar 2018 |
| Sharp-smelling air pollutant | LA Times Daily | 19 Jul 2017 |
| Sharp-smelling air pollutant | The Washington Post | 19 Jul 2017 |
| Sharp-smelling air pollutant | ||
| Smog component |