UV/Vis Stratospheric Air Mass Factors considering photochemistry at Marambio and Belgrano Antarctic stations

Nitrogen dioxide (NO₂), ozone (O₃), chlorine dioxide (OClO), and bromine monoxide (BrO) are key constituents in stratospheric ozone chemistry and have been routinely observed for several decades using Differential Optical Absorption Spectroscopy (DOAS). To convert DOAS differential slant column densities (dSCDs) into geometry-independent vertical column densities (VCDs), accurate Air Mass Factors (AMFs) are required.In this study, stratospheric AMFs for these four trace gases were calculated with the fully spherical radiative transfer model MYSTIC [Mayer, 2009] for the Antarctic stations Belgrano (78°S) and Marambio (64°S). Twilight photochemical effects were taken into account through a photochemical box model coupled to the TOMCAT/SLIMCAT three-dimensional model [Chipperfield et al., 2006]. Vertical concentration profiles generated by this model, were averaged along the corresponding light paths using a ray-tracing approach and subsequently implemented in the spherical radiative transfer calculations.For validation, the derived AMFs and SCDs were evaluated against results from a pseudo-spherical radiative transfer model and against observed slant column densities of NO₂, O₃, OClO, and BrO measured by INTA MAX-DOAS instruments at both Antarctic sites. The modelled SCDs successfully reproduce the measurements within the error bars for NO₂, O₃ and OClO. In the case of BrO, its tropospheric contribution, not considered in the photochemical model, has to be taken into account to find a good agreement.ReferencesMayer, B.: Radiative transfer code in the cloudy atmosphere, European Phys. J. Conferences, 1, 75–99, doi: 10.1140/epjconf/e2009-00912-1, 2009.Chipperfield, M. P.: New version of the TOMCAT/SLIMCAT offline chemical transport model: intercomparison of stratospheric tracer experiments, Q. J. Roy. Meteor. Soc., 132, 1179–1203, doi:10.1256/qj.05.51, 2006.