Contribution of liquid, NAT and ice particles to chlorine activation and ozone depletion in Antarctic winter and spring

Abstract

Abstract. Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and ozone depletion, but the relative roles of different types of polar stratospheric clouds (PSCs) in chlorine activation is an open question. We use multi-year simulations of the chemistryclimate model ECHAM5/MESSy for Atmospheric Chemistry (EMAC) to investigate the impact that the various types of PSCs have on Antarctic chlorine activation and ozone loss.One standard and three sensitivity EMAC simulations have been performed. In all simulations a Newtonian relaxation technique using the ERA-Interim reanalysis was applied to simulate realistic synoptic conditions. In the three sensitivity simulations, we only changed the heterogeneous chemistry on PSC particles by switching the chemistry on liquid, nitric acid trihydrate (NAT) and ice particles on and off. The results of these simulations show that the significance of heterogeneous reactions on NAT and ice particles for chlorine activation and ozone depletion in Antarctic winter and spring is small in comparison to the significance of heterogeneous reactions on liquid particles. Liquid particles alone are sufficient to activate almost all of the available chlorine, with the exception of the upper PSC regions between 10 and 30 hPa, where temporarily ice particles show a relevant contribution. Shortly after the first PSC occurrence, NAT particles contribute a small fraction to chlorine activation.Heterogeneous chemistry on liquid particles is responsible for more than 90 % of the ozone depletion in Antarctic spring in the model simulations. In high southern latitudes, heterogeneous chemistry on ice particles causes only up to 5 DU of additional ozone depletion in the column and heterogeneous chemistry on NAT particles less than 0.5 DU.The simulated HNO 3 , ClO and O 3 results agree closely with observations from the Microwave Limb Sounder (MLS) onboard NASA's Aura satellite.

Comparison of ECHAM5/MESSy Atmospheric Chemistry (EMAC) simulations of the Arctic winter 2009/2010 and 2010/2011 with Envisat/MIPAS and Aura/MLS observations

“…Previous similar but more limited studies focused on the Antarctic. In the study by Kirner et al (2015), for example, only qualitative comparisons of ClO, O 3 , and HNO 3 to Aura/MLS measurements were performed mainly based on multi-year averages. Our study is the first to perform an extensive assessment, both qualitative and quantitative, of the EMAC performance in the Arctic.…”

“…Here, we compare simulations of the Arctic winter stratosphere made with the submodel MSBM (Multi-phase Stratospheric Box Model, formerly PSC; Kirner et al, 2011Kirner et al, , 2015 of the chemistry-climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC; Jöckel et al, 2006Jöckel et al, , 2010 with observations from the Michelson Interferometer for Passive Atmospheric Soundings (Envisat/MIPAS) (Fischer and Oelhaf, 1996;Fischer et al, 2008) and the Aura Microwave Limb Sounder (Aura/MLS) (Waters et al, 2006). The submodel MSBM has been tested and optimized for the simulations of PSCs in the Antarctic (Kirner et al, 2011(Kirner et al, , 2015. EMAC simulation results of stratospheric nitrogen compounds and ozone were evaluated with Envisat/MIPAS observations by Brühl et al (2007) for the Antarctic winter 2002.…”

A climatology of polar stratospheric cloud composition between 2002 and 2012 based on MIPAS/Envisat observations

“…For example, liquid PSC particles alone are sufficient to simulate nearly all of the ozone loss using current model chemistry (Wohltmann et al, 2013;Kirner et al, 2015;Solomon et al, 2015). However, which type of PSs is present at the top of the ozone loss region (between 10 and 30 hPa) is important, as shown for Antarctica by Kirner et al (2015).…”

“…For example, liquid PSC particles alone are sufficient to simulate nearly all of the ozone loss using current model chemistry (Wohltmann et al, 2013;Kirner et al, 2015;Solomon et al, 2015). However, which type of PSs is present at the top of the ozone loss region (between 10 and 30 hPa) is important, as shown for Antarctica by Kirner et al (2015). Further, in the Arctic polar vortex of the 2009/2010 winter 75 the initial activation occurred in PSCs covering only a small portion of the vortex; under such conditions the type of PSC present can be decisive (Wegner et al, 2016).…”

Variability of water vapour in the Arctic stratosphere

“…According to a model study by Kirner et al (2015), 90 % of the ozone depletion in the Antarctic spring is caused by halogen activation on liquid particles. In a model study of the Arctic winter of 2009/2010, Wohltmann et al (2013) showed that chlorine activation on liquid aerosols alone explained the observed changes in the ozone column to within 10 %.…”