Heterogeneous processes play an important role in atmospheric mercury (Hg) reaction; however, the Hg uptake induced by mixed components remains unknown. Here, we developed an integrated approach combining a coated-wall flow tube reactor system with theoretical calculations to investigate the gaseous elemental mercury (Hg (g) 0 ) uptake on the surface of metallic oxides and sodium chloride (NaCl). The mixture of titanium dioxide (TiO 2 ) and NaCl was found to be vital for Hg (g) 0 uptake. This uptake can be enhanced significantly under light irradiation across a range of relative humidity (RH) levels, overcoming the inhibitory effect of higher RH that occurs with TiO 2 alone. The uptake coefficients for the mixture of TiO 2 + NaCl range from 2.10 × 10 –5 to 1.21 × 10 –4 over RH values from 10% to 85%, with the maximum value observed at RH = 25%. In contrast, the uptake on TiO 2 alone was only observed at RH ≤ 55%. Integrated with density functional theory calculations, our results reveal that the synergistically enhanced mechanism of Hg (g) 0 uptake on TiO 2 + NaCl transitions from air–solid to air–liquid interfacial dominate as humidity increases, a process aided by the formation and migration of chloride radicals. These findings highlight a critical, previously overlooked pathway for atmospheric Hg transformation driven by heterogeneous chemistry. Incorporating these effects into global models is essential for improving the accuracy of Hg deposition and associated risk assessments.
Fang et al. (Mon,) studied this question.
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