Influence of air mass histories on radical species during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission

Abstract

The Goddard trajectory chemistry model was used with ER‐2 aircraft data to test our current knowledge of radical photochemistry during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaign. The results of the trajectory chemistry model with and without trajectories are used to identify cases where steady state does not accurately describe the measurements. Over the entire mission, using trajectory chemistry reduces the variability in the modeled NOx comparisons to data by 25% with respect to the same model simulating steady state. Although the variability is reduced, NOx/NOy trajectory model results were found to be systematically low relative to the observations by 20–30% as seen in previous studies. Using new rate constants for reactions important in NOy partitioning improves the agreement of NOx/NOy with the observations but a 5–10% bias still exists. OH and HO2 individually are underpredicted by 15% of the standard steady state model and worsen with the new rate constants. Trajectory chemistry model results of OH/HO2 were systematically low by 10–20% but improve using the new rates constants because of the explicit dependence on NO. This suggests that our understanding of NOx is accurate to the 20% level and HOx chemistry is accurate to the 30% level in the lower stratosphere or better for the POLARIS regime. The behavior of the NOx and HOx comparisons to data using steady state versus trajectory chemistry and with updated rate coefficients is discussed in terms of known chemical mechanisms and lifetimes.