Effects of SO₂ and NH₃ on SA formation from unburned gasoline vapor were investigated in a 30 m³ smog chamber. With the increase in SO₂ and NH₃ concentrations, formation of SA and each of its chemical species was promoted. Meanwhile, NPF and particle size growth were also significantly enhanced. This work indicates that gasoline evaporation emissions will be a significant source of SA and sulfur- and nitrogen-containing organics, especially in the presence of high concentrations of SO₂ and NH₃.