Green’s Dictionary of Slang

1. (Aus.) a mixture of methylated sprits and lemondade.

1946

Truth (Sydney) 28 Apr. 21.1: Metho-Lemon Atom Bombo Blamed For Theft. Harold David Ireland (21) [...] has the next six months as a free guest of His Majesty’s gaolers [...] to consider the atomic properties of a 50-50 mixture of lemonade and methylated spirits.

2. (Aus.) strong, cheap wine; .

1947		Cessnock Eagle (NSW) 31 Oct. 9/2: They must serve out some of the real old ‘stingo,’ or atomic bombo, way down in old Junee.
1950		Biz (Sydney) 28 Sept. 13/2: ‘Spencer’ Wilson won a bottle of atomic bombo and gave a sip all round.
1952		Sun (Sydney) 25 Feb. 1/8: In a little wine shop in the heart of Surry Hills the proprietor has concocted a beaut snort that does the work of half a dozen drinks. [...] They call it the Atom-bombo! Just the thing for quick results.
1953		Baker Aus. Speaks.