| the stratosphere | 0.61 |
| the atmosphere | 0.52 |
| the air | 0.39 |
| two layers of the atmos… | 0.31 |
| higher altitude | 0.25 |
| an ozone transport regi… | 0.25 |
| consist of three oxygen… | 0.61 |
| occur in nature | 0.59 |
| kill bacteria | 0.56 |
| disinfect water | 0.53 |
| form layer | 0.51 |
| protect the earth | 0.48 |
| aggravate asthma | 0.48 |
| deplete formaldehyde | 0.47 |
| deplete chemical flame … | 0.47 |
| revert to oxygen | 0.46 |
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| irritation | 0.47 |
| air pollution | 0.33 |
| damage | 0.33 |
| breathing problems | 0.32 |
| headache | 0.31 |
| chest pain | 0.26 |
| shortness of breath | 0.25 |
| cough | 0.24 |
| chemical reactions | 0.58 |
| passing oxygen | 0.42 |
| lightning | 0.41 |
| sun's ultra-violet rays | 0.33 |
| volatile organic compou… | 0.30 |
| waterfall | 0.25 |
| short life | 0.41 |
| effect | 0.38 |
| short half-life | 0.38 |
| same chemical structure | 0.28 |
| negative effects | 0.26 |
| proven benefits | 0.25 |
| minimum concentration | 0.25 |
| maximum | 0.25 |
| many advantages | 0.24 |
| greater disinfection ef… | 0.23 |
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| gas | 0.62 |
| a greenhouse gas | 0.51 |
| molecule | 0.51 |
| colorless gas | 0.47 |
| occurring substance | 0.41 |
| an allotrope of oxygen | 0.40 |
| triatomic molecule | 0.39 |
| three oxygen molecules | 0.38 |
| triatomic form of oxygen | 0.38 |
| unstable form of oxygen | 0.38 |
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| generated on site | 0.67 |
| used as disinfectant | 0.62 |
| produced | 0.62 |
| formed | 0.59 |
| created in nature | 0.58 |
| produced in the stratos… | 0.55 |
| destroyed | 0.54 |
| used in water treatment | 0.53 |
| produced in upper atmos… | 0.53 |
| formed in the troposphe… | 0.52 |
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