NSRRC Activity Report 2023

Environmental and Earth Sciences 079 Fig. 1 : VUV photoelectron spectra of Lim-SOAs formed during ozonolysis of limonene aerosols at varying levels of ozone and water. (a) O 3 30 ppm, 0% water; (b) O 3 60 ppm, 0% water; (c) O 3 90 ppm, 0% water; (d) O 3 180 ppm, 0% water; (e) O 3 30 ppm, 5% water; (f) O 3 60 ppm, 5% water; (g) O 3 90 ppm, 5% water; (h) O 3 180 ppm, 5% water; (i) O 3 30 ppm, 15% water; (j) O 3 60 ppm, 15% water; (k) O 3 90 ppm, 15% water; (l) O 3 180 ppm, 15% water; (m) O 3 30 ppm, 25% water; (n) O 3 60 ppm, 25% water; (o) O 3 90 ppm, 25% water; (p) O 3 180 ppm, 25% water. Symbol notation: experiment, -◉-; spectral deconvolutions of Feature-I, orange curve; Feature-II, violet curve; Feature-III, pink curve; total fitted spectra at O 3 30 ppm, light magenta curve; at O 3 60 ppm, cyan curve; at O 3 90 ppm, yellow curve; O 3 180 ppm, green curve. [Reproduced from Ref. 2] Chia C. Wang (National Sun Yat-sen University), Yin-Yu Lee (NSRRC), and their research team recently utilized vacuum ultraviolet (VUV) radiation at TLS 21B2 as a photoionization source in aerosol VUV photoelectron spectroscopy to observe the valence electronic structures of limonene aerosols and the secondary organic aerosols (SOAs) generated during limonene ozonolysis for the first time. 2 Limonene is an important naturally occurring monoterpene with very high biogenic emission rates. About 8.6 billion kilograms of limonene are released into the atmosphere every year from natural sources alone, which accounts for about 9% of global monoterpene emissions. Limonene also has a variety of anthropogenic sources, as it is a key component of many household cleaning products, essential oils, air fresheners, and cosmetic products. When limonene-based cleaning products are used indoors, an increase in two orders of magnitude has been reported in the indoor air concentration of limonene compared to outdoor levels. Limonene has been considered one of the most important sources of indoor secondary organic aerosols in domestic environments. The team discovered that higher concentrations of water in limonene aerosols lead to generation of more SOAs. Wang and her research team combined VUV photoelectron spectroscopy, density functional theory quantum