Carbonyl Sulfide (OCS) at the UTLS: Global Observations by MIPAS/Envisat and EMAC Model Results

Abstract:

Carbonyl sulfide (OCS) is an important trace gas in the Earth’s atmosphere. As the predominant long-lived sulfur-containing species in the troposphere it serves as main contributor to the stratospheric aerosol-layer and, thus, indirectly contributes to radiative cooling of the atmosphere. However, the relative contribution of OCS and SO₂ to the Junge-layer is still in debate. Further, OCS can be used as proxy for the photosynthetic uptake of CO₂ due to its similar diffusion pathways into leaves but – in contrast to CO₂ - irreversible uptake. Thus, understanding of global OCS fluxes may contribute to assess gross primary productivity in the biosphere.

In this paper we will present observations of globally and temporally resolved distributions of OCS in the region of the upper troposphere and lower stratosphere over the period 2002-2012 by MIPAS/Envisat. In this dataset various features indicating sources and sinks can be observed for the first time: a region of low OCS concentrations over central S-America and Africa exhibiting an annual cycle, elevated values at the tropopause above the monsoon region and enhanced values in the upper troposphere above the maritime continent in spring. Further, the OCS dataset is correlated with biomass burning tracers from MIPAS, like HCN, to investigate the related emissions of OCS. To interpret the observations and constrain global and regional OCS fluxes, the MIPAS OCS distributions in the UTLS are compared to various simulations with the chemistry transport model EMAC on basis of different emission scenarios