Global Observations of Acetyl Peroxynitrate (PAN) in the Remote Troposphere

We present global airborne observations of acetyl peroxynitrate (CH 3 C(O)OONO 2 , PAN) in the remote troposphere from the Atmospheric Tomography (ATom) campaign. These observations show that biomass burning is the dominant source of PAN in the Southern Hemisphere (SH). In the Northern Hemisphere, anthropogenic emissions from Asia and Europe also contribute significantly to PAN over the Pacific and Atlantic Oceans. Model simulations underestimate PAN in the lower troposphere, in part, due to the underestimation of local production driven by acetaldehyde oxidation and (the ratio of acetyl peroxy radicals reacting with NO 2 relative to other pathways). The significant impacts of biomass burning evident in the ATom PAN observations suggest that improving model treatment of plume transport and the conversion of NO x to PAN in biomass burning plumes is a viable focus for better simulating PAN. Global observations of PAN provide a benchmark for the evaluation of satellite observations and model simulations of PAN.