deed longer than is possible to track with remote measurements.
Here we present detailed composition and aerosol microphysical information obtained from direct observations of pyroCb smoke in 2017. Findings drawn from their analysis are assessed in the context of in situ LS observations dating back to 2006 and are used to quantify the smoke’s average impact on LS composition. The NASA Atmospheric Tomography (ATom) mission (24), using the world’s largest atmospheric research aircraft fully outfitted with state-of-the-art instrumentation (measuring gases, particles, and meteorology), intercepted 2017 pyroCb smoke from the Pacific Northwest in the arctic LS. The aircraft conducted a series of repeated global-scale