308 nm photochemical reaction of gaseous HNO3 and benzene on α-Fe2O3 surfaces

•p-NP was the predominant product of the photochemical reaction of HNO3 and benzene.•p-NP produced from α-Fe2O3 surface was much higher than that in the gas phase.•Photochemical reaction on particle surface was an important source to form SOA.

The 308 nm photochemical reactions of nitric acid (HNO3) and benzene in the gas phase and on α-Fe2O3 surface at 298 K was investigated by using Fourier transform infrared spectroscopy (FT-IR) combined with high performance liquid chromatography (HPLC). The concentration and yield of HONO and p-nitrophenol (p-NP) had been examined as a function of reaction time, benzene initial concentration and relative humidity on photochemical reaction. The results showed that gaseous HNO3 did not directly react with benzene in the dark, and p-NP was formed irradiation under 308 nm UV light. When HNO3 initial concentration was 400 Pa and benzene was 300 Pa, the illumination time was 100 min, the concentration of p-NP produced from the photochemical reaction of HNO3 and benzene on α-Fe2O3 surface was about 3.08 times higher than that in the gas phase. In the meantime, while reaction time was 40 min and relative humidity was 70%, the concentration of HONO and p-NP formed on α-Fe2O3 surface were about 3.55 and 2.51 times higher than those in the gas phase, and the yield of p-NP was 3.74% and 2.99%, respectively. Surfaces effect played a leading role in photochemical reaction of HNO3 and benzene on α-Fe2O3 surface.