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 (PH) and a low ozone concentration period (PL) were defined according to the level of O3 concentration. The average O3 concentration during PH was 117 μg·m-3, and that of PL 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 PH (348085) was higher than in PL (224797), and the proportion of Sec particles (37.1%) in PH was significantly higher than in PL (27.8%), whereas the proportion of EC-aged particles in PH (32.1%) was lower than in PL (44.1%). The proportion of OC-aged particles in PH (13.5%) was slightly higher than in PL (10.4%). The concentration of particles containing nitrate and sulfate showed significant diurnal changes during PH, but no diurnal changes during PL. The peak area of nitrate and sulfate in the Sec particles and EC-aged particles in PH was higher than in PL, which indicates that the amount of nitrate and sulfate produced by the secondary reaction process in PH was more than in PL. 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 PH were significantly higher than those in PL, and showed significant diurnal variation characteristic during PH. The peak appeared 2 h after the peak of O3 concentration. In PL, 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 PH.