Global observations of acetyl peroxynitrate (PAN) in the remote troposphere

We present global airborne observations of acetyl peroxynitrate (CH3C(O)OONO2, 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 βNO2 (the ratio of acetyl peroxy radicals reacting with NO2 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 NOx 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. Plain Language Summary We report the global airborne observations of acetyl peroxynitrate (PAN) from the Atmospheric Tomography (ATom) campaign. Biomass burning is the dominant source of PAN over the remote oceans in the Southern Hemisphere. Anthropogenic emissions from Asia and Europe significantly contribute to PAN levels over the Pacific and Atlantic Oceans, alongside biomass burning. Model simulations underestimate PAN in the lower oceanic troposphere, partly due to an underestimation in local production driven by acetaldehyde. Our observations show strong evidence of the persistent biomass burning influence on PAN throughout the remote troposphere, particularly over the Southern Hemispheric oceans. This work provides a valuable data set to improve understanding of the global distribution of PAN.