Sat-J: A Satellite-Derived Dataset of Global Atmospheric Photolysis Rates

Photolysis—the breaking of chemical bonds by sunlight—is the primary driving force for reactive atmospheric chemistry. Photolysis reactions directly and indirectly control a host of air pollutants and greenhouse, particularly through the production of the hydroxyl radical (OH), the main oxidizing agent in the troposphere, by photolysis of ozone (O₃). Despite the critical importance of atmospheric photochemistry for understanding and predicting air pollution and greenhouse gas levels, the rates of photolysis reactions (J values) are highly uncertain. State-of-the-art air quality and climate models differ in their global-mean J values by a factor of 2, and likely much more on regional and seasonal scales. We describe a new, global, 3-D dataset of photolysis rates that is derived from satellite observations of clouds, aerosols, and trace gases, together with a computationally efficient photolysis code. This “Sat-J” product is validated against in situ observations from aircraft and used to evaluate a 3-D atmospheric chemistry model.