[Impact of Differents in the Concentrations of Ozone on the Chemical Composition of Single Particles]

To investigate the effect of high concentration of ozone (O₃) on the aerosol formation and aging process, this study made observations using a single-particle aerosol mass spectrometer (SPAMS) at Heshan Atmospheric Environment Supervision Station in Guangdong Province in October 2018. During the observation period, a high ozone concentration period (P_H) and a low ozone concentration period (P_L) were defined according to the level of O₃ concentration. The average O₃ concentration during P_H was 117 μg·m^-3, and that of P_L was 25 μg·m^-3. According to the difference in chemical composition, single particles mainly included aging element carbon particles (EC-aged), secondary particles (Sec), and aging organic carbon particles (OC-aged) during the observation period. The total number of single particles in P_H (348085) was higher than in P_L (224797), and the proportion of Sec particles (37.1%) in P_H was significantly higher than in P_L (27.8%), whereas the proportion of EC-aged particles in P_H (32.1%) was lower than in P_L (44.1%). The proportion of OC-aged particles in P_H (13.5%) was slightly higher than in P_L (10.4%). The concentration of particles containing nitrate and sulfate showed significant diurnal changes during P_H, but no diurnal changes during P_L. The peak area of nitrate and sulfate in the Sec particles and EC-aged particles in P_H was higher than in P_L, which indicates that the amount of nitrate and sulfate produced by the secondary reaction process in P_H was more than in P_L. In addition, the peak areas of nitrate and sulfate in the Sec particles were significantly higher than those in the EC-aged particles, indicating that the age of the Sec particles was greater. In this study, acetate (⁵⁹CH₃CO₂^-) and glyoxal (⁷³C₂HO₃^-) were selected to represent the changing characteristics of aldehyde and ketone compounds in single-particle aerosols. The number concentration and peak area of ⁵⁹CH₃CO₂^- and ⁷³C₂HO₃^- in Sec and OC-aged particles in P_H were significantly higher than those in P_L, and showed significant diurnal variation characteristic during P_H. The peak appeared 2 h after the peak of O₃ concentration. In P_L, the peak value was significantly reduced, and the change trend was the same as that of the number concentration of Sec and OC-aged particles, indicating that high concentration of O₃ is beneficial to the oxidation of VOCs to ⁵⁹CH₃CO₂^- and ⁷³C₂HO₃^-. In summary, high concentration of O₃ and enhancement of secondary species in single particles were due to the strong photochemical reactions during P_H.