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The tropospheric ozone depletion event (ODE), first observed at Barrow (now known as Utqiaġvik), Alaska, is a phenomenon that frequently occurs during the springtime in the Arctic. In this study, we performed a three-dimensional model study on ODEs occurring at Barrow and its surrounding areas between 28 March and 6 April 2019 using a 3-D multi-scale air quality model, CMAQ (Community Multiscale Air Quality Modeling System). Several ODEs observed at Barrow were captured, and two of them were thoroughly analyzed using the process analysis method to estimate contributions of horizontal transport, vertical transport, dry deposition, and the overall chemical process to the variations in ozone and bromine species during ODEs. We found that the ODE occurring between 30 and 31 March 2019 (referred to as ODE1) was primarily caused by the horizontal transport of low-ozone air from the Beaufort Sea to Barrow. The formation of this low-ozone air over the sea was largely attributed to a release of sea-salt aerosols from the Bering Strait under strong wind conditions, stemming from a cyclone generated on the Chukotka Peninsula. It was also discovered that the surface ozone dropped to less than 5 ppb over the Beaufort Sea, and the overall chemical process contributed up to 10 ppb to the ozone loss. Moreover, BrO over the sea reached a maximum of approximately 80 ppt. This low-ozone air over the sea was then horizontally transported to Barrow, leading to the occurrence of ODE1. Regarding another ODE on 2 April (ODE2), we found that its occurrence was also dominated by the horizontal transport from the sea, but under the control of an anticyclone. The termination of this ODE was mainly attributed to the replenishment of ozone-rich air from the free troposphere by a strong vertical transport. [ABSTRACT FROM AUTHOR]

Accurate meteorological simulations are important in response to the rapid climate change and insufficient meteorological observations in the Arctic. In this study, we assessed the performance of the Weather Research and Forecasting (WRF) model in simulating meteorological parameters at two Arctic stations (Barrow and Summit) in April 2019, by using measurements and statistical parameters. Sensitivity tests for different planetary boundary layer (PBL) schemes, four-dimensional data assimilation (FDDA) and sea surface temperature (SST) were also performed to reveal their impacts on the accuracy of model simulations. The results demonstrated that the WRF model performs the best in predicting the surface pressure but the worst in predicting the winds at these two stations. The sensitivity tests showed that among the four tested PBL schemes (ACM2, MYJ, BL and YSU), the model equipping with the MYJ scheme behaves the best in predicting the meteorological parameters especially the winds at these two Arctic stations. Applying FDDA nudging methods can also significantly increase the accuracy of simulations. In addition, we found that updating a time-varying SST in the model may bring a two-sided influence on meteorological simulations in the Arctic, especially at coastal stations. • MYJ scheme was found to perform the best in predicting the winds at the two Arctic stations. • Applying FDDA nudging methods decrease the deviations in simulations of meteorological parameters, especially the winds. • Updating the SST exerts a stronger impact on simulations at the coastal station than at the inland station. [ABSTRACT FROM AUTHOR]

Ozone depletion events (ODEs) in the springtime of the Arctic have been frequently observed since the early 1980s, and the correlation between the ozone mixing ratio during the ODEs and the nitrogen oxides (NOx) concentration is still unclear. In the present study, the role of the background level of NOx in ODEs was investigated by using a box model implementing a chemical reaction mechanism containing 49 chemical species and 141 related reactions. A concentration sensitivity analysis was also applied to discover the dependence of the ozone mixing ratio during the ODEs on each constituent of the initial air composition. The simulation results showed that a critical value of the NOx background level exists, with which the ozone depletion rate is independent of the initial concentration of NOx, and the critical value was found to be approximately 55 ppt (ppt = part per trillion, 10−12 mol/mol) in the present study. The concentration sensitivity analysis also showed that the existence of NOx has a two-sided impact on the depletion of ozone, depending on the initial amount of NOx. With a low background level of NOx (less than 55 ppt), the increase of the initial NOx can advance the ozone depletion. On the contrary, with a high initial NOx level (more than 55 ppt), NOx would delay the consumption of ozone during the ODEs. [ABSTRACT FROM AUTHOR]