Hydrogen sulfide gas is also known as "sewer gas"...

English as a Second Language English Vocabulary, Grammar and Idioms
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idph.state.il.us/envhealth/f … ulfide.htm
Hydrogen sulfide gas is [color=red]also known as “sewer gas” because it is often produced by the breakdown of waste material. At low levels, hydrogen sulfide gas has a strong odor similar to rotten eggs. You can smell hydrogen sulfide gas at lower levels than may cause health effects, so smelling the gas does not always mean that it will make you sick. However, at higher levels, your nose can become overwhelmed by the gas and you cannot smell it. At higher levels, hydrogen sulfide gas can make you sick and could be fatal.

Is the “also” necessary?

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It is not “necessary,” but it is very helpful.

“Also” indicates that both names may be known to some considerable extent. If I say something, such as a person, is known as something else, it implies the first title may be obscure.

Norma Jeane Mortenson was known as Marylin Monroe.
Stefani Joanne Germanotta is known as Lady Gaga.

That works well because, in either case, the real name is not well-known.

Edward Kennedy was also known as Ted Kennedy.

Both his names are well-known, so I would use “also” to clear things up.

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Thank you, Mordant.