Bingham Research Center, Utah State University, Vernal, Utah 84078, United States.
Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
Environ Sci Technol. 2022 Aug 16;56(16):11225-11235. doi: 10.1021/acs.est.2c02224. Epub 2022 Jul 25.
Mercury pollution is primarily emitted to the atmosphere, and atmospheric transport and chemical processes determine its fate in the environment, but scientific understanding of atmospheric mercury chemistry is clouded in uncertainty. Mercury oxidation by atomic bromine in the Arctic and the upper atmosphere is well established, but less is understood about oxidation pathways in conditions of anthropogenic photochemical smog. Many have observed rapid increases in oxidized mercury under polluted conditions, but it has not been clearly demonstrated that these increases are the result of local mercury oxidation. We measured elemental and oxidized mercury in an area that experienced abundant photochemical activity (ozone >100 ppb) during winter inversion (i.e., cold air pools) conditions that restricted entrainment of air from the oxidized mercury-rich upper atmosphere. Under these conditions, oxidized mercury concentrations decreased day-upon-day, even as ozone and other pollutants increased dramatically. A box model that incorporated rapid kinetics for reactions of elemental mercury with ozone and OH radical overestimated observed oxidized mercury, while incorporation of slower, more widely accepted reaction rates did not. Our results show that rapid gas-phase mercury oxidation by ozone and OH in photochemical smog is unlikely.
汞污染主要排放到大气中，而大气传输和化学过程决定了其在环境中的归宿，但大气汞化学的科学认识仍存在不确定性。在北极和高层大气中，原子溴对汞的氧化作用已得到充分证实，但在人为光化学烟雾条件下的氧化途径却知之甚少。许多人观察到在污染条件下氧化汞的迅速增加，但还没有明确证明这些增加是由于当地的汞氧化。我们在一个经历了丰富光化学反应（臭氧 >100 ppb）的地区测量了元素汞和氧化汞，在冬季逆温（即冷空气团）条件下，这限制了来自富氧化汞高层大气的空气的卷入。在这些条件下，即使臭氧和其他污染物急剧增加，氧化汞的浓度也逐日下降。一个包含了元素汞与臭氧和 OH 自由基快速反应动力学的箱式模型高估了观测到的氧化汞，而包含了更慢、更被广泛接受的反应速率则没有。我们的结果表明，光化学烟雾中臭氧和 OH 对汞的快速气相氧化不太可能发生。
