This sequence of chemical equations describes the series of reactions that can be triggered by the presence of hydrocarbons in the atmosphere, in this case methane. Type the formula for the correct species into each gap in the sequence.

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| + | CH4 | → | CH3 | + | H2O | (1) |
| + | CH3 | → | CH3O2 | | | (2) |
| + | CH3O2 | → | CH3O | + | | (3) |
| + | CH3O | → | HO2 | + | | (4) |
| + | HO2 | → | OH | + | | (5) |