Abstract: Aqueous reactions play an important role in the formation of secondary organic aerosols, and related research has become one of the hotspots in the field of atmospheric aerosols. The typical aqueous reaction system of glyoxal/ammonium sulfate was selected in this work. Based on a smog chamber simulation system, the particle size and composition of glyoxal/ammonium sulfate aqueous secondary organic aerosol were measured using a scanning mobility particle sizer and a vacuum ultraviolet photoionization time-of-flight mass spectrometer. By comparing with the reaction under dark conditions, the influence mechanism of ultraviolet light on the particle size and composition of glyoxal/ammonium sulfate aqueous secondary organic aerosol under different relative humidity was explored. It shows that ultraviolet light can induce the photolysis of light absorbing substances such as imidazole and imidazole-2- carboxaldehyde in the products of glyoxal/ammonium sulfate aqueous reaction, and relative humidity can affect their photolysis process. Under low and medium relative humidity conditions, the photolysis rate increases with the increase of relative humidity, while under high relative humidity, the photolysis phenomenon almost does not occur. These results are not only helpful to understand the optical properties of atmospheric secondary organic aerosols, but also provide an important reference for the modification of regional climate models.

Key words: glyoxal, ammonium sulfate, aqueous phase secondary organic aerosols, ultraviolet, particle size