2023, Min, Ning, Yao, Jun, Li, Hao, Chen, Zhihui, Pang, Wancheng, Zhu, Junjie, Kümmel, Steffen, Schaefer, Thomas, Herrmann, Hartmut, Richnow, Hans Hermann

The photosensitized transformation of organic chemicals is an important degradation mechanism in natural surface waters, aerosols, and water films on surfaces. Dissolved organic matter including humic-like substances (HS), acting as photosensitizers that participate in electron transfer reactions, can generate a variety of reactive species, such as OH radicals and excited triplet-state HS (3HS*), which promote the degradation of organic compounds. We use phthalate esters, which are important contaminants found in wastewaters, landfills, soils, rivers, lakes, groundwaters, and mine tailings. We use phthalate esters as probes to study the reactivity of HS irradiated with artificial sunlight. Phthalate esters with different side-chain lengths were used as probes for elucidation of reaction mechanisms using 2H and 13C isotope fractionation. Reference experiments with the artificial photosensitizers 4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein (Rose Bengal), 3-methoxy-acetophenone (3-MAP), and 4-methoxybenzaldehyde (4-MBA) yielded characteristic fractionation factors (−4 ± 1, −4 ± 2, and −4 ± 1‰ for 2H; 0.7 ± 0.2, 1.0 ± 0.4, and 0.8 ± 0.2‰ for 13C), allowing interpretation of reaction mechanisms of humic substances with phthalate esters. The correlation of 2H and 13C fractions can be used diagnostically to determine photosensitized reactions in the environment and to differentiate among biodegradation, hydrolysis, and photosensitized HS reaction.

2022, Guo, Jia, Zhang, Xiaoshan, Gao, Yi, Wang, Zhangwei, Zhang, Meigen, Xue, Wenbo, Herrmann, Hartmut, Brasseur, Guy Pierre, Wang, Tao, Wang, Zhe

Increasing surface ozone (O3) concentrations has emerged as a key air pollution problem in many urban regions worldwide in the last decade. A longstanding major issue in tackling ozone pollution is the identification of the O3 formation regime and its sensitivity to precursor emissions. In this work, we propose a new transformed empirical kinetic modeling approach (EKMA) to diagnose the O3 formation regime using regulatory O3 and NO2 observation datasets, which are easily accessible. We demonstrate that mapping of monitored O3 and NO2 data on the modeled regional O3-NO2 relationship diagram can illustrate the ozone formation regime and historical evolution of O3 precursors of the region. By applying this new approach, we show that for most urban regions of China, the O3 formation is currently associated with a volatile organic compound (VOC)-limited regime, which is located within the zone of daytime-produced O3 (DPO3) to an 8h-NO2 concentration ratio below 8.3 ([DPO3]/[8h-NO2] ≤ 8.3). The ozone production and controlling effects of VOCs and NOx in different cities of China were compared according to their historical O3-NO2 evolution routes. The approach developed herein may have broad application potential for evaluating the efficiency of precursor controls and further mitigating O3 pollution, in particular, for regions where comprehensive photochemical studies are unavailable.

2022, Shen, Jiali, Scholz, Wiebke, He, Xu-Cheng, Zhou, Putian, Marie, Guillaume, Wang, Mingyi, Marten, Ruby, Surdu, Mihnea, Rörup, Birte, Baalbaki, Rima, Amorim, Antonio, Ataei, Farnoush, Bell, David M., Bertozzi, Barbara, Brasseur, Zoé, Caudillo, Lucía, Chen, Dexian, Chu, Biwu, Dada, Lubna, Duplissy, Jonathan, Finkenzeller, Henning, Granzin, Manuel, Guida, Roberto, Heinritzi, Martin, Hofbauer, Victoria, Iyer, Siddharth, Kemppainen, Deniz, Kong, Weimeng, Krechmer, Jordan E., Kürten, Andreas, Lamkaddam, Houssni, Lee, Chuan Ping, Lopez, Brandon, Mahfouz, Naser G. A., Manninen, Hanna E., Massabò, Dario, Mauldin, Roy L., Mentler, Bernhard, Müller, Tatjana, Pfeifer, Joschka, Philippov, Maxim, Piedehierro, Ana A., Roldin, Pontus, Schobesberger, Siegfried, Simon, Mario, Stolzenburg, Dominik, Tham, Yee Jun, Tomé, António, Umo, Nsikanabasi Silas, Wang, Dongyu, Wang, Yonghong, Weber, Stefan K., Welti, André, Wollesen de Jonge, Robin, Wu, Yusheng, Zauner-Wieczorek, Marcel, Zust, Felix, Baltensperger, Urs, Curtius, Joachim, Flagan, Richard C., Hansel, Armin, Möhler, Ottmar, Petäjä, Tuukka, Volkamer, Rainer, Kulmala, Markku, Lehtipalo, Katrianne, Rissanen, Matti, Kirkby, Jasper, El-Haddad, Imad, Bianchi, Federico, Sipilä, Mikko, Donahue, Neil M., Worsnop, Douglas R.

Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements.