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To investigate the effect of high concentration of ozone (O 3 ) 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 O 3 concentration. The average O 3 concentration during P H . 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 -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 ( 59 CH 3 CO 2 - ) and glyoxal ( 73 C 2 HO 3 and enhancement of secondary species in single particles were due to the strong photochemical reactions during - ) were selected to represent the changing characteristics of aldehyde and ketone compounds in single-particle aerosols. The number concentration and peak area of 59 CH 3 CO 2 - and 73 C 2 HO 3 - 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 O 3 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 O 3 is beneficial to the oxidation of VOCs to 59 CH 3 CO 2 - and 73 C 2 HO 3 - . In summary, high concentration of O 3 and enhancement of secondary species in single particles were due to the strong photochemical reactions during P H .