While searching for cosmic dust and debris from nuclear bomb tests, Christian Junge discovered in 1960 a layer of microscopic aerosol particles between the tropopause and about 18 miles (30 km) altitude. These particles are composed of sulfuric acid and water and are formed by the chemical transformation of sulfur-containing gases . This layer is called the Junge Layer or the Stratospheric Aerosol Layer (http://www.albany.edu/faculty/rgk/atm101/junge.htm). According to Solomon et al. (2011; Science) recent measurements demonstrate that the "background” stratospheric aerosol layer is persistently variable rather than constant, even in the absence of major volcanic eruptions. Several independent data sets show that stratospheric aerosols have increased in abundance since 2000. Near-global satellite aerosol data imply a negative radiative forcing due to stratospheric aerosol changes over this period of about –0.1 watt per square meter, reducing the recent global warming that would otherwise have occurred. Observations from earlier periods are limited but suggest an additional negative radiative forcing of about –0.1 watt per square meter from 1960 to 1990. Climate model projections neglecting these changes would continue to overestimate the radiative forcing and global warming in coming decades if these aerosols remain present at current values or increase.
There is a paper in press discussing that here:
Kremser and 34 others, in press, "Stratospheric aerosol - Observations, processes, and impact on climate"
http://orbi.ulg.ac.be/bitstream/2268/195878/1/Kremser_et_al-2016-Reviews_of_Geophysics.pdf
Indeed, the Kremser et al paper is highly recommended, more insights into dynamical mechanisms you'll find in my 2015 ACP paper:
http://www.atmos-chem-phys.net/15/5557/2015/
Very interesting work Mr. McDonald. One of the most crucial issues which are discussed is that the non-sulfate contributions to the stratospheric aerosol are not accounted for in most chemistry-climate models to date, but they could play an important role in heterogeneous chemical reactions and for the nucleation/condensation of saturated gaseous compounds. I think that it is very difficult to estimate non-sulfate contributions to the stratospheric aerosols. Will we estimate those in the future?
Hi George,
Glad to hear you found Kremser et al useful. However, I am not an active researcher in that field. Perhaps Dr Hommel will be kind enough to answer your question.
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