急問'Why striking a match can absorb smell e.g. unpleasant sme

Striking a match to "absorb" smell is not quite a correct statement.
I would rather say the smell of the match cover the original smell.
Actually, the "head" of a match contain phosphorus that can be ignited upon striking. The combustion of the phosphorus-containing compound would generate odorous compounds that cover the original smell. Also, the flame itself helps to destroy the sulphur-containing molecules in the bad smell. Therefore, strikking a match could help to cover the smell.

The lower explosion limit of town gas is about 4.7%. When the air composes of 4.7% or above town gas, striking a match (or any occurence of flame) would result in explosion. The smell from town gas would likely to disappear as most of the town gas would be consumed in the explosion. Yet I do not recommend you to try this.