Dr. Milton is a pioneer of the modern science of airborne transmission of respiratory viruses. Starting in the late 1990s, he proposed that monitoring carbon dioxide concentrations indoors could be used as a marker for risk of respiratory virus transmission. The idea initially met with derision. His original paper demonstrating a mathematical model illustrating the concept was rejected at Science and other journals before being published by Indoor Air in 2003. He supported this concept with epidemiologic studies published in several journals between 1998 and 2004. Today, his idea has gained wide acceptance and is now promoted by many scientists and public health experts as a means of identifying high risk environments for the spread of COVID-19. His work also provided a key piece of the scientific basis for masks mandates that are now common throughout the world including the publication of a key paper April 1, 2020 that was downloaded over two million times during the first year of the pandemic.