Photochemical Transformation Mechanism Of HNO₃ With Benzene And Anisole On Atmospheric Mineral Particle （SiO₂、α-Fe₂O₃ And α-FeOOH） Surfaces

308 nm photochemical reaction of gaseous nitric acid (HNO3) and benzene or anisole in the gas phase and on mineral particle (SiO2, α-FezO3 and α-FeOOH) surfaces were studied by using Fourier transform infrared spectroscopy (FT-IR) and high performance liquid chromatography (HPLC). The influences of reaction time, benzene or anisole, relative humidity (RH), temperature, particle size and ultraviolet (UV) light wavelength on photochemical reactions were systematically investigated, respectively. Moreover, the reaction mechanism of photochemical reactions on particle surfaces was also studied. The knowledge on photochemical reaction had the important theoretical significance for understanding the formation mechanism of secondary organic aerosol in the atmosphere. The main results were described blew.No nitrophenol product was formed in the dark reaction of gaseous HNO3 and benzene in the gas phase and on particle surfaces. Under 308 nm irradiation, the main product was p-nitrophenol (p-NP). The concentration of p-NP increased with the increase of illumination time, benzene, relative humidity and temperature. In order of the concentration of p-NP formed from photochemical reaction of HNO3 and benzene on particle surfaces, it goes:α-FeOOH> α-Fe2O3>SiO2> gas phase. When HNO3 was 400 Pa, benzene was 300 Pa and irradiation was 100 min, the concentration of p-NP formed from photochemical reaction of gaseous HNO3 and benzene on SiO2, α-Fe2O3 and α-FeOOH surfaces were 2.26×1013,3.45×1013 and 3.57×1013 molecule/cm3, and they were about 2.02,3.08 and 3.19 times higher than those in the gas phase, respectively. When benzene was 600 Pa, the concentration of p-NP produced from photochemical reaction of HNO3 and benzene on three kind of particle surfaces were about 1.86,3.16 and 3.41 times higher than those in the gas phase, respectively. In the presence of water vapor, HONO was formed in the reaction. When relative humidity was 70%, the concentration of p-NP produced from photochemical reaction of HNO3 and benzene on three kind of particle surfaces were about 2.01,3.41 and 3.67 times higher than those in the gas phase, respectively. The concentration of HONO on three kinds of particle surfaces was about 2.71,3.55 and 3.63 times higher than those in the gas phase, respectively.The primary product was p-NP in the dark reaction and photochemical reaction of HNO3 and anisole in the gas phase and on mineral particle surfaces, and the concentration of p-NP formed in the photochemical reaction was significantly larger than dark reaction. Meanwhile, the concentration of p-NP increased with increasing irradiation time, anisole and temperature. However, the concentration of p-NP decreased with the increase of relative humidity. In order of the concentration of p-NP formed from photochemical reaction of HNO3 and anisole on particle surfaces, it goes: α-FeOOH>α-Fe2O3>SiO2>gas phase. When HNO3 was 400 Pa, anisole was 300 Pa and illumination time was 100 min, the concentration of p-NP formed on SiO2, α-Fe2O3 and α-FeOOH surfaces were 14.60×1013,18.23×1013 and 20.16×1013 molecule/cm3, and they were about 2.39,2.98 and 3.30 times higher than those in the gas phase, respectively. When relative humidity was 70%, the concentration of p-NP produced on three kind of particle surfaces were about 2.39,2.98 and 3.28 times higher than those in the gas phase, respectively.According to the in-cloud oxidation model in atmosphere environment, the rate of p-NP formed from the photochemical reactions of HNO3 and benzene or anisole increased with increasing liquid water concentration. And the rate of p-NP formed on particle surfaces significantly larger than that in the gas phase. Surfaces effect played the leading role in the photochemical reaction of gaseous HNO3 and benzene or anisole on mineral particle surfaces.