Day: August 15, 2025

A new study led by NOAA Research has confirmed that a substantial amount of groundwater contamination caused by perchlorates, a class of toxic chlorine-based chemicals, originates in a surprising place – the stratosphere. The study, led by researchers at NOAA’s Chemical Sciences Laboratory (CSL) and published in the journal Proceedings of the National Academies of Science, provides new evidence linking perchlorate formation to tiny airborne particles (aerosols) in the stratosphere, the layer of the atmosphere 7 to 30 miles above Earth’s surface.

The study analyzed detailed aerosol chemical measurements collected from high-altitude research aircraft in the lower stratosphere, where the vast majority of particles in the thin air are made of sulfur dioxide. But the scientists found perchlorates were almost entirely bound to aerosol particles originating from biomass burning and nitrogen-rich sources, which are transported into the stratosphere by atmospheric circulation and by towering plumes of wildfire smoke. While these particles make up only a small fraction of the total stratospheric aerosol population, they carry nearly all of its perchlorate load.