Intercontinental Transport of Peroxyacyl Nitrates (PANs) from CrIS Observations

Peroxyacyl Nitrates (PANs) are an important family of photochemically produced trace gasses that serve as the principal reservoir species for tropospheric nitrogen dioxide radicals (NO_x = NO + NO₂). PANs are formed through the oxidation of non-methane volatile organic compounds (NMVOCs) in the presence of NO_x and allow NO_x to be transported long distances to facilitate efficient production of ozone (O₃) downwind of NO_x source regions. Consistent long-term in-situ observations over the oceans are generally limited, so we leverage new global satellite observations of PANs from the Cross-track Infrared Sounder (CrIS) on the Suomi National Polar-orbiting Partnership (S-NPP) satellite to evaluate the seasonal and interannual variations of intercontinental transport in the Northern Hemisphere since 2016. We find there are pronounced seasonal cycles in the abundance of PANs over both ocean basins, where April and July are dominant months for transpacific transport of PANs and summer months (June, July and August) are dominant months for transatlantic transport. Some of the interannual variability in monthly mean observed PANs over the North Pacific can be explained by wildfire activity in Siberia. CrIS is used to further explore changes to the intercontinental transport of PANs associated with major decreases in precursor emissions in response to COVID-19. Preliminary analysis indicates decreases in the abundance of PANs over mid-latitudes during some months of 2020. Our analysis demonstrates that space-based observations provided by CrIS can advance understanding of pollutant transport across ocean basins.