Mario Molina
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Obituary Mario Molina (1943–2020) Ozone-hole Nobel winner, Montreal Protocol advocate, presidents’ adviser. n the mid-1970s, Mario Molina helped to be much less efficient than is observed in the predict that global emissions of chloro- lab or in the environment. Molina suggested fluorocarbons (CFCs) could deplete strat- that the difference might be due to a disordered ospheric ozone. A decade later, scientists surface layer, or quasi- liquid layer, on ice. At the at the British Antarctic Survey reported Massachusetts Institute of Technology (MIT) in Ithat a vast hole had appeared in the ozone Cambridge, his research group did experiments layer over the South Pole. Molina’s tireless confirming that hydrogen chloride at low strat- advocacy and scientific diplomacy helped to ospheric temperatures induced such disorder, bring about the 1987 Montreal Protocol on and that it played a part in activating chlorine. Substances that Deplete the Ozone Layer, an While he was institute professor at MIT international agreement to phase out CFCs between 1989 and 2004, Molina and his and other ozone-depleting chemicals. Molina then-wife and long-time collaborator, Luisa shared the 1995 Nobel Prize in Chemistry with Tan Molina, began work on air quality in his former adviser F. Sherwood Rowland and mega cities (broadly, those with more than the Dutch chemist Paul Crutzen for their ten million inhabitants) in the global south. work on stratospheric chemistry. He died on To steer policy, the Mexico City Project com- 7 October, aged 77. bined unprecedented large-scale field studies The Montreal Protocol, the first United of atmospheric chemistry in urban neighbour- Nations treaty to achieve universal ratification, hoods, involving hundreds of international reduced stratospheric chlorine and bromine, scientists, with in-depth analysis and stake- and the ozone hole has begun to recover. In holder engagement. This work improved the MONIER/GAMMA-RAPHO/GETTY LOUIS 2003, former UN secretary-general Kofi Annan ozone hole, and concluded with the Montreal air quality in his beloved home city. described the treaty as “perhaps the single most Protocol. However, basic questions remained In 2004, Molina relocated to UC San Diego successful international agreement to date”. Its unanswered: why was the ozone hole localized and founded the Mario Molina Center for implementation, and Molina’s later work on air over the South Pole, and seasonal? Strategic Studies on Energy and the Environ- quality in megacities, and on climate change, Molina found the answer in the surface chem- ment, a think tank based in Mexico City. In his improved the quality of life for millions world- istry of ice particles that make up the beautiful last decades, he spent increasing time in Mexico, wide. A treasured public figure in the United ‘mother of pearl’ polar stratospheric clouds but remained an inspirational faculty member at States and Mexico, he was a trusted adviser to (PSCs) observed during the winter over the UC San Diego. In 2014, he spearheaded a major US president Barack Obama. South Pole. During the dark, cold polar winter, public-outreach initiative on climate change, Born in Mexico City, the son of a diplomat, stratospheric chlorine is stored in the relatively ‘What we know’, for the American Association Molina went to boarding school in Switzerland. for the Advancement of Science. He studied chemical engineering at the National “His work on air quality Molina could communicate the essence of Autonomous University of Mexico, in his home a technical issue to anyone, with gentle diplo- city, and applied chemistry at the University of in megacities improved macy and scientific credibility. He served as Freiburg, Germany. Doctoral studies in physical the quality of life for a scientific adviser to several presidents of chemistry at the University of California (UC), millions worldwide.” Mexico, and, as a member of the Vatican’s Berkeley, brought him to the United States, Pontifical Academy of Sciences, he advised where he built his career. three popes and co- authored the 2017 report At UC Irvine, he and Rowland calculated the inert forms of gas-phase chlorine nitrate, ‘Well Under 2 Degrees Celsius: Fast Action threat posed by CFCs to the atmosphere (see hypochlorous acid and hydrogen chloride. Policies to Protect People and the Planet from M. Molina and F. Rowland Nature 249, 810–812; Molina and his research group, then at Extreme Climate Change’ (see go.nature. 1974). The chemical inertness that made CFCs the Jet Propulsion Laboratory in Pasadena, com/2hzsB1). In his final months, he advocated valuable as refrigerants and propellants also California, did creative experiments to mimic passionately for mask-wearing to reduce the prevents oxidation removing them from the PSC particles: reactions between ice surfaces transmission of SARS-CoV-2 in Mexico. atmosphere, where they become a Trojan horse and chlorine compounds led to the release of for introducing chlorine to the stratosphere. chlorine. The winter build-up of the gas in the V. Faye McNeill is a professor in the There the gas can catalyse the destruction of Antarctic polar vortex due to such reactions departments of chemical engineering and ozone, allowing harmful high-energy ultravi- leads to intense ozone depletion when sunlight environmental science at Columbia University, olet (UVB) light to penetrate to Earth’s surface. returns in the polar spring. New York. Molina was her PhD adviser at Communicating this work to the media A mystery remained as to why ice should be MIT from 2000 to 2004. She co-organized and policymakers was Molina’s initiation into such an efficient catalyst for these stratospheric a symposium in his honour in 2014, and in scientific diplomacy. These efforts created processes. Calculations based on the reactions 2015 co-edited his Festschrift special issue in momentum for the phasing out of CFCs in aer- of hydrogen chloride with a crystalline ice sur- The Journal of Physical Chemistry A. osol cans, accelerated by the discovery of the face predicted that chlorine activation would e-mail: [email protected] Nature | Vol 587 | 12 November 2020 | 193 ©2020 Spri nger Nature Li mited. All rights reserved. .