Sulfur Exposure for Airplane Passengers From Stratospheric Aerosol Injection

Injection of sulfur dioxide to create a stratospheric sulfate aerosol cloud is the most studied method of climate intervention. It has been suggested that airplanes be used at high latitudes to create such a cloud at lower altitudes. Commercial airplanes routinely fly at altitudes of 11 km in the Arctic, and therefore passengers could be exposed to sulfur from the clouds. We show here, based on calculations from three Earth system models, UKESM1, CESM2-WACCM6, and E3SMv3, simulating 6 Tg SO₂ injections in each hemisphere per year that the resulting sulfuric acid concentration would be about 5–45 μg H₂SO₄/m³ inside the cabin on the average, but could be much higher on some flights. As the air quality exposure guideline is 50 μg H₂SO₄/m³ for an 8-hr exposure, the potential hazard requires further research. The hazard would depend on the injection scenario, with more massive injections producing more hazardous conditions.