3D simulations of tropospheric ozone depletion events using WRF-Chem

Abstract

Abstract. Tropospheric bromine release and ozone depletion events (ODEs) as they commonly occur in the Arctic spring are studied using the regional software WRF-Chem. For this purpose, the MOZART-MOSAIC chemical reaction mechanism is extended by bromine and chlorine reactions as well as an emission mechanism for reactive bromine via heterogeneous reactions on ice and snow surfaces. The simulation domain covers an area of 5,040 km x 4,960 km, centered north of Utqiagvik (formerly Barrow), Alaska, and the time interval from February through May, 2009. Several simulations for different strengths of the bromine emission are conducted and evaluated by comparison with in-situ and ozone-sonde measurements of ozone mixing ratios as well as by comparison with tropospheric BrO vertical column densities (VCDs) from the Global Ozone Monitoring Experiment–2 (GOME-2) satellite instrument. The base bromine emission scheme includes the direct emission of bromine due to bromide oxidation by ozone through the reactive surface ratio β of the ice/snow surface relative to a flat surface. 10 Results of simulations with β = 1.0 agree well with the observations, however, a value of 1.5 performs somewhat better. The bromine emission due to bromide oxidation by ozone is found to be important to provide an initial seed for the bromine explosion. Consideration of halogen chemistry substantially improves the prediction of the ozone mixing ratio with respect to the observations. Meteorological nudging is found to be essential for a good prediction of ODEs over the three months period.

Implementation and Impacts of Surface and Blowing Snow Sources of Arctic Bromine Activation Within WRF‐Chem 4.1.1

“…It also involves heterogeneous recycling on aerosols present within the atmosphere to sustain halogen activation. This mechanism has been tested in the 3D models GEM-AQ and EMAC (Toyota et al, 2011(Toyota et al, , 2014Falk & Sinnhuber, 2018), and very recently WRF-Chem (Herrmann et al, 2021).…”

“…These well-known ozone depletion events (ODEs) are tied to the presence of enhanced concentrations of reactive bromine in the atmosphere (Barrie et al, 1988), including species such as Br 2 , BrO, Br, HOBr, and BrNO 3 (Platt & Hönninger, 2003;Simpson et al, 2007b;Abbatt et al, 2012;Pratt et al, 2013;Simpson et al, 2015). Although the link between increased bromine in the atmosphere and ozone depletion events was discovered over three decades ago (Barrie, 1986), developing predictive model descriptions of bromine emissions and chemistry in polar regions remains a challenge (Yang et al, 2008;Toyota et al, 2011;Falk & Sinnhuber, 2018;Fernandez et al, 2019;Huang et al, 2020;Herrmann et al, 2021).…”