Triplet-State Photochemistry of Dissolved Organic Matter: Triplet-State Energy Distribution and Surface Electric Charge Conditions

Abstract

Excited triplet states of chromophoric dissolved organic matter (3CDOM*) are highly reactive species in sunlit surface waters and play a critical role in reactive oxygen species (ROS) formation and pollutant attenuation. In the present study, a series of chemical probes, including sorbic acid, sorbic alcohol, sorbic amine, trimethylphenol, and furfuryl alcohol, were employed to quantitatively determine 3CDOM* and 1O2 in various organic matters. Using a high concentration of sorbic alcohol as high-energy triplet states quencher, 3CDOM* can be first distinguished as high-energy triplet states (>250 kJ mol–1) and low-energy triplet states (<250 kJ mol–1). The terrestrial-origin natural organic matter (NOM) was found to mainly consist of low-energy triplet states, while high-energy triplet states were predominant in autochthonous-origin NOM and effluent/wastewater organic matter (EfOM/WWOM). The 1O2 quantum yields and electron transfer quantum yield coefficients (f TMP) generated from low-energy triplet states remained constant in all tested organic matters. External phenolic compound showed quenching effects on triplet-state formation and tended to have a higher quenching efficiency for aromatic ketone triplet states, which are the main high-energy triplet states. In comparison with terrestrial-origin NOM, autochthonous-origin NOM and EfOM/WWOM presented lower reaction rate constants for sorbic amines and higher reaction rate constants for sorbic acid, and these differences are likely due to dissimilar surface electric charge conditions. Understanding the triplet-state photochemistry of CDOM is essential for providing useful insights into their photochemical effects in aquatic systems.

Photooxidants from brown carbon and other chromophores in illuminated particle extracts

“…This is nearly 260 times higher than the average quantum yield of q OH. Our quantum yields for singlet oxygen formation in PM extracts are similar to values previously reported for surface water organics (e.g., 2 %-5 % in Zhou et al (2019).…”

“…The average (±1σ ) oxidizing triplet quantum yield in standard extracts is (2.4 ± 1.0) % (Table S13), approximately 2 times lower than the value for 1 O 2 * (Table S7) but 150 times higher than for q OH (Table S3). Our triplet quantum yields are within the wide range of values that has been reported for surface waters, approximately 0.4 %-7 % (Zepp et al, 1985;Grebel et al, 2011;Zhou et al, 2019).…”

Triplet State Formation of Chromophoric Dissolved Organic Matter in Atmospheric Aerosols: Characteristics and Implications

“…Lin et al (2014) showed the reaction ability and transformation mechanism of 3 CDOM* formed by humic acid using the TMP probe. Zhou et al (2019) has reported the 3 CDOM* energy distribution using TMP and SA probes. Compared with other chemical probes, TMP contains methyl-substituted groups that can be used as electron donors for 3 CDOM* reactions; thus, TMP has a higher reactivity (Canonica & Freiburghaus, 2001).…”

“…The energy levels of different 3 CDOM* is different. TMP, as a triplet-state probe used in this study, has remarkable electron transfer characteristics and is related to the energy of 3 CDOM* (Zhou et al, 2019). Approximately 70% of high-energy 3 CDOM* https://doi.org/10.5194/acp-2019-1032 Preprint.…”

“…Previous studies on 3 CDOM* are mainly about the water environment, such as sewers, terrestrial natural waters and oceans (Bodhipaksha et al, 2015;Erickson et al, 2018;Zhou et al, 2019), few studies have explored the atmospheric environment. In recent years, the CDOM in atmospheric aerosols, atmospheric fog water and rainfall has been widely found to have a strong photochemical reactivity.…”