My goodness, some of the chemicals they are mentioning are completely tenuous in the context of spray tan solutions... MSG is monosodium glutamate, which is a flavour enhancer; you're more likely to find it in a bag of crisps or a Chinese takeaway than in a bottle of spray tan solution!
Tartrazine is a yellow/green dye found in cheap sweets and fizzy pop; I guess it's feasible that it might turn up in a bottle of "el cheapo" spray tan solution, perhaps as one of the constituents of the guide colour, but it's not going to have much effect (if any at all) at browning your skin.
Benzophenone-3 is a sunscreen...
Oxybenzone - Wikipedia, the free encyclopedia - so I guess it would have some use in protecting the skin from UV if present in tanning solutions.
Sulphur Dioxide would probably be present, if at all, as a preservative. But there are other substances that I'd expect to see in spray tan solutions rather than sulphur dioxide; the parabens, for example, or DMDM-Hydantoin.
However, none of the above chemicals are what I'd consider essential ingredients in tanning solutions; the key ingredients in tanning solutions being DHA (dihydroxyacetone), which they did mention in the article - but which is pretty harmless (you could quite happily eat it without much if any in the way of ill effects, as it would be processed by your body as a sugar) - likewise with erythulose, which is a 4-carbon sugar (whereas DHA is a 3-carbon sugar). Then some tanning solutions might possibly contain juglone (walnut oil) or lawsone (from henna), which stain the skin brown via a process called Michael addition - which I think off the top of my head is different chemically from the Maillard reaction where DHA and erythulose react with amino acids in the skin. While I'd be less inclined to want to risk eating juglone or lawsone (versus DHA or erythulose), I'd consider neither to be a particularly nasty chemical when applied to the skin by a trained professional in accordance with the product's instructions.
