Mario Molina, ozone, air pollution and climate

Photo: México Desconocido

On 7 October, the day that the 2020 Nobel Prize in chemistry was announced, the world lost Mario Molina. I lost an influential teacher. 

Mario Molina was the only Mexican ever to receive the Nobel Prize in chemistry, which he was awarded in 1995 together with his postdoctoral adviser at the University of California,  Irvine, F. Sherwood Rowland, and their Dutch colleague Paul Crutzen.    

The 1995 Nobel chemistry prize honoured their discovery of the role played by anthropogenic chemicals in destroying ozone in the upper atmospheric layer called the stratosphere. Since the 1920s people had been using chlorofluorocarbons (CFCs) as refrigerants and propellants. 

Designed in the laboratory, CFCs were nontoxic, nonflammable and considered completely safe. Little did people know that new unintended dangers were hidden in their refrigerators, air conditioners and spray cans. 

Mario Molina receiving the CCAC's Climate and Clean Air award in San Francisco in September 2018. Photo: ARNICO PANDAY

In the 1970s Molina and Rowland realised that CFCs could reach the stratosphere, where the sun would break them apart, releasing reactive chlorine radicals that would attack ozone. Ozone in the stratosphere plays a key role, blocking ultraviolet rays (UV) from the sun. 

Without sufficient ozone in the stratosphere, dangerous amounts of UV could reach the earth’s surface, damaging plants and causing skin cancer. In the mid-1980s alarmingly low levels of ozone were discovered in the stratosphere over Antarctica. Mario Molina, together with his then wife Luisa Molina, provided the winning explanation of what caused the Antarctic Ozone Hole.

In 1987 the world’s nations signed the Montreal Protocol on Substances that Deplete the Ozone Layer, agreeing to a rapid phasing out of CFCs and similar gases. In the decades that followed, the stratospheric ozone layer has repaired itself. 

The Montreal Protocol is still considered to be one of the most successful international environmental agreements. Driven by scientific results showing that the world was heading in a dangerous direction, world leaders came together to remove from use the substances that were responsible. The Montreal Protocol is seen as a model, or at least an inspiration, for dealing with greenhouse gases that are driving global climate change. 

I had the good fortune of having Mario Molina as my teacher. In Spring 2000 he taught atmospheric chemistry to me and four other first-year doctoral students at the Massachusetts Institute of Technology (MIT). He was one of the most humble and self-effacing teachers I have ever had. 

No student question was too stupid for him, and he was passionate about making us understand. One time he spent more than three hours, late into the evening, standing at the board in his office, helping me navigate a particularly difficult homework set.  

While my primary doctoral advisor at MIT was Ronald Prinn, the New Zealander whose global AGAGE network monitored atmospheric levels of CFCs and other gases at remote locations around the world, Mario was an influential second advisor on my doctoral committee. I spent countless hours talking to Mario about my research and about my plans in life. 

Mario had come to the US for his PhD, had settled and risen to stardom in the US, and only started advising the government in his home country Mexico after he won the Nobel Prize. I was passionate about returning to and contributing to Nepal without waiting as long.

While I worked on my doctoral field research on air pollution in the Kathmandu Valley, Mario led international teams of researchers studying the air pollution problem in Mexico City – a bowl shaped valley that once had the world’s worst air pollution. 

They provided policy relevant scientific answers that helped drive the massive cleaning up of Mexico City’s air over the past two decades, providing inspiration to my work on air pollution since my return to Nepal.  

While I never managed to get Mario to visit Nepal, I was lucky to see him again in recent years at international meetings around the world. He was a member of the Climate and Clean Air Coalition (CCAC)’s Scientific Advisory Panel, while I served on the CCAC’s Steering Committee. 

The last time I saw him was at the Global Climate Action Summit in San Francisco in September 2018.  Like all great scientists, Mario was a life-long learner. He moved from topic to topic, while speaking out on issues that mattered.  At the CCAC we worked on promoting an integrated approach to reducing both air pollution and climate change globally.  


Arnico Panday is the CEO of Ullens Education Foundation. Previously he served as Regional Programme Manager of the Atmosphere Programme at ICIMOD.

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