First comprehensive analysis of sulfur dioxide concentration in the stratosphere/10 years. Measurements on board of ENVISAT find no identifiable anthropogenic sources of sulfur dioxide.
Trace gases and aerosols are major factors influencing the climate. With the help of highly complex installations, such as MIPAS on board of the ENVISAT satellite, researchers try to better understand the processes in the upper atmosphere. They present the most comprehensive overview of sulfur dioxide measurements online in the Atmospheric Chemistry and Physics Discussions forum for review (doi:10.5194/acpd-13-12389-2013).
"Sulfur compounds up to 30 km altitude may have a cooling effect," Michael Höpfner, the KIT scientist responsible for the study, says. For example, sulfur dioxide (SO2) and water vapor react to sulfuric acid that forms small droplets, called aerosols, that reflect solar radiation back into universe. "To estimate such effects with computer models, however, the required measurement data have been lacking so far." MIPAS infrared spectrometer measurements, however, produced a rather comprehensive set of data on the distribution and development of sulfur dioxide over a period of ten years.
Based on these results, major contributions of the sulfur budget in the stratosphere can be analyzed directly. Among others, carbonyl sulfide (COS) gas produced by organisms ascends from the oceans, disintegrates at altitudes higher than 25 km, and provides for a basic concentration of sulfur dioxide. The increase in the stratospheric aerosol concentration observed in the past years is caused mainly by sulfur dioxide from a number of volcano eruptions. "Variation of the concentration is mainly due to volcanoes," Höpfner explains. Devastating volcano eruptions, such as those of the Pinatubo in 1991 and Tambora in 1815, had big a big effect on the climate. The present study also shows that smaller eruptions in the past ten years produced a measurable effect on sulfur dioxide concentration at altitudes between 20 and 30 km. "We can now exclude that anthropogenic sources, e.g. power plants in Asia, make a relevant contribution at this height," Höpfner says.
"The new measurement data help improve consideration of sulfur-containing substances in atmosphere models," Höpfner explains. "This is also important for discussing the risks and opportunities of climate engineering in a scientifically serious manner."
MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) was one of the main instruments on board of the European environmental satellite ENVISAT that supplied data from 2002 to 2012. MIPAS was designed by the KIT Institute of Meteorology and Climate Research. All around the clock, the instrument measured temperature and more than 30 atmospheric trace gases. It recorded more than 75 million infrared spectra. KIT researchers, together with colleagues from Forschungszentrum Jülich, have now developed the MIPAS successor GLORIA that may be the basis of a future satellite instrument for climate research.

Atmos. Chem. Phys. Discuss., 13, 12389-12436, 2013

Sulfur dioxide (SO2) as observed by MIPAS/Envisat: temporal development and spatial distribution at 15–45 km altitude

M. Höpfner1, N. Glatthor1, U. Grabowski1, S. Kellmann1, M. Kiefer1, A. Linden1, J. Orphal1, G. Stiller1, T. von Clarmann1, and B. Funke2
1Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
2Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain

Abstract. We present a climatology of monthly and 10° zonal mean profiles of sulfur dioxide (SO2) volume mixing ratios (vmr) derived from MIPAS/Envisat measurements in the altitude range 15–45 km from July 2002 until April 2012. The vertical resolution varies from 3.5–4 km in the lower stratosphere up to 6–10 km at the upper end of the profiles with estimated total errors of 5–20 pptv for single profiles of SO2. Comparisons with few available observations of SO2 up to high altitudes from ATMOS, for a volcanically perturbed situations from ACE-FTS and, at the lowest altitudes, with stratospheric in-situ observations reveal general consistency of the datasets. The observations are the first empirical confirmation of features of the stratospheric SO2 distribution which have only been shown by models up to now: (1) the local maximum of SO2 at around 25–30 km altitude which is explained by the conversion of carbonyl sulfide (COS) as the precursor of the Junge layer, and (2) the downwelling of SO2 rich air to altitudes of 25–30 km at high latitudes during winter and its subsequent depletion on availability of sunlight. This has been proposed as the reason for the sudden appearance of enhanced concentrations of condensation nuclei during Arctic and Antarctic spring. Further, the strong increase of SO2to values of 80–100 pptv in the upper stratosphere through photolysis of H2SO4 has been confirmed. Lower stratospheric variability of SO2 could mainly be explained by volcanic activity and no hint for a strong anthropogenic influence has been found. Regression analysis revealed a QBO (quasi-biennial oscillation) signal of the SO2 time series in the tropics at about 30–35 km, a SAO (semi-annual oscillation) signal at tropical and subtropical latitudes above 32 km and annual periodics predominantly at high latitudes. Further, the analysis indicates a correlation with the solar cycle in the tropics and southern subtropics above 30 km. Significant negative linear trends are found in the tropical lower stratosphere, probably due to reduced tropical volcanic activity and at southern mid-latitudes above 35 km. A positive trend is visible in the lower and middle stratosphere at polar to subtropical southern latitudes.

Citation: Höpfner, M., Glatthor, N., Grabowski, U., Kellmann, S., Kiefer, M., Linden, A., Orphal, J., Stiller, G., von Clarmann, T., and Funke, B.: Sulfur dioxide (SO2) as observed by MIPAS/Envisat: temporal development and spatial distribution at 15–45 km altitude, Atmos. Chem. Phys. Discuss., 13, 12389-12436, doi:10.5194/acpd-13-12389-2013, 2013.