1Institute of Environmental Physics, University of Bremen, Bremen,
2Centre for Atmospheric Chemistry, School of Chemistry, University of
Wollongong, Wollongong, Australia
3Colorado State University, Fort Collins, CO, USA
4Carnegie Institute of Washington, Stanford, CA, USA
5University of East Anglia, Norwich, UK
6Institute of Astrophysics and Geophysics, University of Liège,
7National Center for Atmospheric Research, Boulder, CO, USA
8Department of Physics, University of Toronto, Toronto, Canada
9University of California, Merced, CA, USA
10Princeton University, Princeton, NJ, USA
11Bodeker Scientific, Alexandra, New Zealand
Received: 03 Jul 2015 – Discussion started: 25 Sep 2015
Abstract. Understanding carbon dioxide (CO2) biospheric processes is of great importance because the terrestrial exchange drives the seasonal and interannual variability of CO2 in the atmosphere. Atmospheric inversions based on CO2 concentration measurements alone can only determine net biosphere fluxes, but not differentiate between photosynthesis (uptake) and respiration (production). Carbonyl sulfide (OCS) could provide an important additional constraint: it is also taken up by plants during photosynthesis but not emitted during respiration, and therefore is a potential means to differentiate between these processes. Solar absorption Fourier Transform InfraRed (FTIR) spectrometry allows for the retrievals of the atmospheric concentrations of both CO2 and OCS from measured solar absorption spectra. Here, we investigate co-located and quasi-simultaneous FTIR measurements of OCS and CO2 performed at five selected sites located in the Northern Hemisphere. These measurements are compared to simulations of OCS and CO2 using a chemical transport model (GEOS-Chem). The coupled biospheric fluxes of OCS and CO2 from the simple biosphere model (SiB) are used in the study. The CO2 simulation with SiB fluxes agrees with the measurements well, while the OCS simulation reproduced a weaker drawdown than FTIR measurements at selected sites, and a smaller latitudinal gradient in the Northern Hemisphere during growing season when comparing with HIPPO (HIAPER Pole-to-Pole Observations) data spanning both hemispheres. An offset in the timing of the seasonal cycle minimum between SiB simulation and measurements is also seen. Using OCS as a photosynthesis proxy can help to understand how the biospheric processes are reproduced in models and to further understand the carbon cycle in the real world.
Revised: 18 Jan 2016 – Accepted: 04 Feb 2016 – Published: 25 Feb 2016
Wang, Y., Deutscher, N. M., Palm, M., Warneke, T., Notholt, J., Baker, I., Berry, J., Suntharalingam, P., Jones, N., Mahieu, E., Lejeune, B., Hannigan, J., Conway, S., Mendonca, J., Strong, K., Campbell, J. E., Wolf, A., and Kremser, S.: Towards understanding the variability in biospheric CO2 fluxes: using FTIR spectrometry and a chemical transport model to investigate the sources and sinks of carbonyl sulfide and its link to CO2, Atmos. Chem. Phys., 16, 2123-2138, doi:10.5194/acp-16-2123-2016, 2016.