A Study of New Particle Formation from Ozonolysis of α-Pinene

• Main Authors: Hao-Wei Peng, 彭浩維
• Other Authors: 洪惠敏
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/b7hquq

碩士 === 國立臺灣大學 === 大氣科學研究所 === 105 === In this study, the new particle formation from the ozonolysis of α-pinene as a function of initial ozone concentration ([O3]i) and relative humidity (RH) was studied using a scanning mobility particle sizer spectrometer (SMPS) to monitor the size distribution of submicrometer particles at room temperature. How the radicals produced from the chemical reactions and the impact of the addition of anthropogenic emissions (SO2) on the particle formation were investigated. The applied initial concentration of α-pinene (19.3 ppm and 15.4 ppm) was much higher than [O3]i (0.04 - 0.12 ppm), and RH was controlled at < 1 %, 36 % and 54 %. A box model was constructed to simulate the concentration of products with possible chemical reactions while a particle spectral model was applied to simulate the particle size distribution, with the adjustment of physical processes and chemical kinetic parameters of the products such as the saturation vapor pressure, nucleation and condensation rate of products. The results showed a positive correlation of the produced SOA to [O3]i in both number and mass concentration for [O3]i in the range of 0.05 - 0.12 ppm. It is likely due to the produced low-volatility products reaching the saturation point at [O3]i = 0.05 ppm. The saturation vapor pressure was estimated to be 3.7 × 10^-10 - 1.6 × 10^-8 bar by model simulation. For a given [O3]i, SOA mass concentration showed a decreasing trend with RH. It is surmised that water vapor may react with HO2 to form HO2•H2O, which decreases the overall oxidation of α-pinene-O3 system. With the addition of 3900 ppm of methanol vapor, a scavenger of OH, the new particle formation was then almost inhibited. By simulations, it was estimated that at most 27 % of HO2 radical and 79 % of OH radical were consumed by water and methanol vapor, respectively. With the addition of 6.3 ppm of SO2, one of the major anthropogenic emissions, a significant enhancement of smaller particles in number and mass concentration was observed likely due to the formation of H2SO4 from the reaction of SO2¬ with OH radical. By model simulation, it was estimated to have 0.35 ppb of H2SO4, which might lead to significant nucleation rate. A significant faster nucleation rate from our experimental system than that of H2SO4-H2O binary system with the same concentration of H2SO4 and H2O might suggest the importance of the produced organic species for the multi-component nucleation of H2SO4-H2O-organic system. This study illustrated the new particle formation from the ozonolysis of α-pinene at different environments and suggested the importance of radicals, which might be extended to other organic compound systems. The nucleation and condensation processes from the model simulations might provide other regional models the possible physical and chemical parameters required to estimate the number and mass concentration of aerosols formed in such processes in real atmosphere.