Yellow gas is generated during the discharge of the mixed acid

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I would like to ask fellow sailors: our company has encountered a strange issue recently. The mixed acid waste in barrels that we acquired from other companies (mainly a mixture of phosphoric acid and sulfuric acid generated from anodizing in the electronics industry) – when this acid was poured into the trench by gravity, during the pouring of the third barrel of acid, a pale yellow, irritating gas with a sulfur smell suddenly emerged from the trench. The first bucket contained 52.3% phosphoric acid and 8% sulfuric acid, respectively; the second bucket had 22% phosphoric acid and 24% sulfuric acid, respectively; the third bucket contained 51% phosphoric acid and 5% sulfuric acid, respectively. Apart from phosphoric acid and sulfuric acid, most of the rest in the spent acid is water. At first, we suspected that it was the chlorides that, through a reaction, displaced chlorine gas. But it still hasn’t been determined yet; it’s not clear how the yellow gas is produced. Please help analyze this; I’m waiting online. Thank you