Evolution of PAN in wildfire smoke plumes detected by the Cross-Track Infrared Sounder (CrIS) over the western US during summer 2018.

We calculate peroxyacetyl nitrate (PAN) excess mixing ratios normalized by CO (NEMRs) in fresh smoke plumes from fires and follow the evolution as these plumes are transported several hours to days downwind. We utilize data from the Cross-Track Infrared Sounder (CrIS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite, which continues the thermal infrared peroxyacetyl nitrate (PAN) satellite record established by the Tropospheric Emission Spectrometer (TES) onboard the Aura satellite. CrIS provides improved spatial resolution, allowing for improved analysis opportunities. Here we present an analysis of CrIS PAN retrievals over the western US during the summer 2018 wildfire season. The analysis period coincides with the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) which collected a comprehensive suite of gas and aerosol phase measurements in more than 20 fresh smoke plumes. CrIS is capable of detecting PAN and CO enhancements from smoke plumes sampled during WE-CAN, especially those that became active before the satellite overpass or burned for several days ( e.g., Carr Fire, Mendocino Complex Fire). This analysis shows that elevated PAN within smoke plumes can impact atmospheric photochemistry up to several states downwind from the fire source. The combination of high CrIS spatial resolution and favorable background conditions on 13 September 2018 permits detecting chemical changes within the Pole Creek smoke plume in Utah. In this plume, CrIS PAN NEMRs increase from less than 1% to 3.5% within 3 - 4 hours of physical aging. These results are within the range observed in fresh plumes sampled during WE-CAN, where PAN NEMRs increased from 1.5% to 4% within 4 hours of physical aging.