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.