Hydrosulfuric acid in this paper is thought to be better at radiation management over sulfates and other methods, in a manner similar to that of the Mt. Pinatubo eruption (aerosol injection event) of 1992. It is found that on average, the radius of H2SO4 engineered aerosols is smaller than SO2 or on par with non-engineered environments.

The result is that less sulfur is needed to cool -4 W m-2 by H2SO4 than SO2. Ozone reduction is still strongly suspected in the lower stratosphere, but on the surface (pun most definitely intended), this method seems to be a viable alternative to stratospheric aerosol enhancement via SO2. The Harvard Project’s calcite experiments came 6 years after the Pierce paper was published in 2010; CaCO3 is a much sexier option because it actually promotes ozone formation, claims a “10-fold less” radiative heating of the lower stratosphere compared to an effective load of sulfate aerosol, and is a non-toxic chemical found in tap water, often a neutralizing agent.

Still I’m left wondering which communities elected to be a part of these experiments; the equator crosses countries in South America, Africa, and Southeast Asian Island nations. Latitude degrees between 30 °S and 30 °N also cover dozens of more countries including the United States. Practically speaking, researchers likely chose a longitude across a body of water such as the Atlantic or Pacific- but let’s also assume that the plane flown needs to be relatively close to land to refuel. Were communities within a 100 mile radius informed of the potential spike in sulfur content of their water or warned of the smell… I understand how unlikely it is for nearly any of these particles to fall back onto earth’s surface but NASA should really be more careful about what chemicals it let’s fly into our atmosphere (which is a large but sensitive ecosystem).

One data point I would have liked to see in this paper is the carbon footprint of the aircraft(s) used in the experiment. An independent study, using data from the US Department of Transportation, claims that commercial airliners produce as much as 53 lbs of CO2 per mile. How many miles did each aircraft travel in each of these experiments? The world may never know…..

https://doi.org/10.1029/2010GL043975

https://blueskymodel.org/air-mile