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

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 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 ( ⁵⁹ CH ₃ CO ₂ ^- ) and glyoxal ( ⁷³ C ₂ HO ₃ ^- ) 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 .