| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 101 === Aerosol particles play an important role in precipitation by acting as ice and cloud condensation nuclei, which also affect atmospheric radiation, and make impact on the ecosystem. There are many sources of aerosol formation. It can either be produced by human activities, or formed through nature processes. The particle size distribution depends on the nucleation, condensation and coagulation processes. With the presence of existing particles, the nucleation process might be alternated due to the condensation of gas phase chemical species which can contribute to the nucleation process. Besides, the collision between the existing particles with the nucleated particles can also affect the overall aerosol size distribution.
In this study, the new particle formation via moisture air exposed to ultraviolet radiation is quantified and the impact of the existing particles on such particle nucleation process is investigated. Two types of existing particles are studies; ammonium sulfate and commercial black carbon representing as soluble and insoluble particles, respectively. The observed particles generated from the moisture air exposed to ultraviolet radiation are mainly in the nuclei mode with mode size of 7 nm and the total number concentration is dependent on the relative humidity of the air flow. The total number concentration of nucleated particles is more significantly decreased with the presence of ammonium sulfate particles than that of black carbon particles. With further model study, the existing particles can affect the new particles formation mainly by the condensation process than the coagulation process (less than 1%) for this study. As to the mechanism for the new particle formation under ultraviolet radiation, the simulated concentration of hydrogen peroxide for the given experimental condition is too low to formed particles by binary nucleation with water, which suggests there are other mechanisms or species such as other reactive trace gases involved in the process.
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