Sensitivity of aerosol distribution and climate response to stratospheric SO₂ injection locations

Injection of SO₂ into the stratosphere has been proposed as a method to, in part, counteract anthropogenic climate change. So far, most studies investigated injections at the equator or in a region in the tropics. Here we use Community Earth System Model version 1 Whole Atmosphere Community Climate Model (CESM1(WACCM)) to explore the impact of continuous single grid point SO₂ injections at seven different latitudes and two altitudes in the stratosphere on aerosol distribution and climate. For each of the 14 locations, 3 different constant SO₂ emission rates were tested to identify linearity in aerosol burden, aerosol optical depth, and climate effects. We found that injections at 15^∘N and 15^∘S and at 25 km altitude have equal or greater effect on radiation and surface temperature than injections at the equator. Nonequatorial injections transport SO₂ and sulfate aerosols more efficiently into middle and high latitudes and result in particles of smaller effective radius and larger aerosol burden in middle and high latitudes. Injections at 15^∘S produce the largest increase in global average aerosol optical depth and increase the change in radiative forcing per Tg SO₂ /yr by about 15% compared to equatorial injections. High-altitude injections at 15^∘N produce the largest reduction in global average temperature of 0.2^∘ per Tg S/yr for the last 7 years of a 10 year experiment. Injections at higher altitude are generally more efficient at reducing surface temperature, with the exception of large equatorial injections of at least 12 Tg SO₂ /yr. These findings have important implications for designing a strategy to counteract global climate change.