| Similarity | Rank | |
|---|---|---|
| sulphur | 0.902 | 6647 |
| carbon | 0.897 | 3195 |
| nitrogen | 0.878 | 6386 |
| monoxide | 0.848 | 12904 |
| emission | 0.820 | 3620 |
| hydrocarbon | 0.815 | 12320 |
| oxide | 0.813 | 7892 |
| co2 | 0.812 | 18793 |
| nitrous | 0.805 | 29606 |
| nox | 0.801 | 28969 |
| &sub2; | 0.800 | 34174 |
| tetrachloride | 0.794 | 38419 |
| methane | 0.794 | 11786 |
| particulate | 0.793 | 25930 |
| pollutant | 0.778 | 10281 |
| chlorine | 0.772 | 10537 |
| cfc | 0.771 | 9251 |
| nitric | 0.771 | 22052 |
| chlorofluorocarbon | 0.759 | 24061 |
| vocs | 0.758 | 67555 |
| photochemical | 0.755 | 30345 |
| ethane | 0.749 | 70857 |
| phosgene | 0.748 | 98640 |
| benzene | 0.748 | 21692 |
| ozone | 0.746 | 5037 |