Explicit calculation of indirect global warming potentials for halons using atmospheric models

Abstract

Abstract. The concept of Global Warming Potentials (GWPs) has been extensively used in policy consideration as a relative index for comparing the climate impact of an emitted greenhouse gas (GHG), relative to carbon dioxide with equal mass emissions. Ozone depletion due to emission of chlorinated or brominated halocarbons leads to cooling of the climate system in the opposite direction to the direct warming contribution by halocarbons as GHGs. This cooling is a key indirect effect of the halocarbons on climatic radiative forcing, which is accounted for by indirect GWPs. With respect to climate, it is critical to understand net influences considering direct warming and indirect cooling effects especially for Halons due to the greater ozone-depleting efficiency of bromine over chlorine. Until now, the indirect GWPs have been calculated using a parameterized approach based on the concept of Equivalent Effective Stratospheric Chlorine (EESC) and the observed ozone depletion over the last few decades. As a step towards obtaining indirect GWPs through a more robust approach, we use atmospheric models to explicitly calculate the indirect GWPs of Halon-1211 and Halon-1301 for a 100-year time horizon. State-of-theart global chemistry-transport models (CTMs) were used as the computational tools to derive more realistic ozone depletion changes caused by an added pulse emission of the two major Halons at the surface. The radiative forcings on climate from the ozone changes have been calculated for indirect GWPs using an atmospheric radiative transfer model (RTM). The simulated temporal variations of global average total column Halons after a pulse perturbation follow an exponential decay with an e-folding time which is consistent with the expected chemical lifetimes of the Halons. Our cal-

Potential impact of iodinated replacement compounds CF<sub>3</sub>I and CH<sub>3</sub>I on atmospheric ozone: a three-dimensional modeling study

“…The larger CF 3 I ODPs for tropical emissions can be explained by the rapid vertical transport due to convective activities in equatorial regions that is more effective in the vertical transport of total halogens since the transport timescale in convection events (hours) is shorter than chemical loss or washout removal timescale. Youn et al (2009) showed that the differences between time variations of Halon perturbations and ozone changes, simulated by both the 2-D and 3-D models, were found not to give significantly different values for both the direct and indirect GWPs. Trace gas changes in perturbed model atmosphere for the calculation of ODP are determined with two steady-state (perturbed and baseline) model atmospheres for each scenario so that the limitation of the 2-D model mostly related to zonally-asymmetric features such as tropospheric circulation and stratospheric ozone hole does not signify in this study of evaluating potential impacts on global ozone using the two simulations.…”

“…However, the 2-D model runs in this study of evaluating the impact of VSL compounds on atmospheric ozone were conducted in more detailed integration with a time step of 20 min due to extremely short lifetimes of the source and product gases although the above-mentioned limitations exist. The 2-D model still has the advantage of being much more computationally efficient compared to 3-D models, and thus can provide a quick reference to the slower 3-D simulations (Youn et al, 2009). …”

“…The UIUC 2-D CRT model (see Youn et al, 2006Youn et al, , 2009Guillas et al, 2006) updated from the version used in Li et al (2006) is also used. The UIUC 2-D CRT model includes a 3-D representation of the propagation of low wave-number planetary waves, and thus is called as "2.5-D model" in the sense that transport and diffusion effects due to the breaking of the waves are self-consistently handled with the zonal wind and the residual mean meridional circulation (mass transport circulation).…”

“…The UIUC 2-D CRT model includes a 3-D representation of the propagation of low wave-number planetary waves, and thus is called as "2.5-D model" in the sense that transport and diffusion effects due to the breaking of the waves are self-consistently handled with the zonal wind and the residual mean meridional circulation (mass transport circulation). Wave propagation properties and the residual circulation, calculated with climatological data from United Kingdom Meteorological Office (UKMO) data assimilation system for the specific years 1992-2002, are computed self-consistently with the zonal wind, and tracers are transported in the zonal-mean plane by the residual circulation and the diffusion due to the wave breaking (Choi and Youn, 2001;Youn et al, 2009). …”

Aviation 2006 NO<sub>x</sub>-induced effects on atmospheric ozone and HO<sub>x</sub> in Community Earth System Model (CESM)

“…Earlier versions of the UIUC RTM have been used in previous research (e.g., Jain et al, 2000;Naik et al, 2000;Youn et al, 2009;Patten et al, 2011). The UIUC RTM calculates the flux of solar and terrestrial radiation across the tropopause.…”