[Krosan]

Here is a 2018 article from Nature saying:

“The process does not have to be wildly expensive; in a report last month, the Intergovernmental Panel on Climate Change suggested that a fleet of high-flying aircraft could deposit enough sulfur to offset roughly 1.5 °C of warming for around $1 billion to $10 billion per year.”

https://www.nature.com/articles/d41586-018-07533-4

[lepton]

Here is a paper from 2010: https://www.pnas.org/content/107/38/16428

I’m thinking of something going back into the possibly early 1990s. Oppenheimer/Teller...one of the A-Bomb folks.