Even though the particles, droplets, whatever do range in size from about 0.1 to 1 microns, the ones larger than 0.6 are generally already in the troposphere and don't matter as far as scattering effectiveness. Between 65,000 and 90,000 ft, they range from 0.6 to 0.2-0.4 with the largest ones over the equator at 65,000 ft. So, I don't think this would be a problem, but if it turned out this way, we would be dealing with essentially Pinatubo-sized aerosol and the quantities would be larger than required for the background type aerosol. I can't think of any practical way to ionize the aerosol or even the gas once it is dispersed. Bear in mind, this is a model and not necessarily how a precursor gas would actually perform, whether OCS or SO2 or H2S. ----- Original Message ----- From: Ken Caldeira To: [EMAIL PROTECTED] Cc: [email protected] Sent: Tuesday, December 09, 2008 11:27 AM Subject: [geo] Re: Carbonyl Sulfide, the Forgotten Precursor
While it is not brought out very strongly in the poster, the real contribution of this work seems to me to be the more detailed treatment of particle aggregation. Even though they are starting out with a well distributed gas, the sulfate particles grow in size to a few tenths of a micron effective radius (and some exceed 1 micron). An obvious area for innovation is developing strategies to avoid particle aggregation. (Is there a way to maintain a charge on the particles?) ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [EMAIL PROTECTED]; [EMAIL PROTECTED] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Tue, Dec 9, 2008 at 6:33 AM, Alvia Gaskill <[EMAIL PROTECTED]> wrote: http://ei.colorado.edu/siteadmin/images/files/file_155.pdf Poster examines the impact of using carbonyl sulfide as a source of sulfate aerosols on stratospheric ozone depletion. Problem is, there is no such source available or possible. The decline in halogen gases in the stratosphere over time is also ignored and only the impact on offsetting a doubling of CO2 is considered as if that was required today. The poster does in one panel do a good job of explaining the differences in the sulfur loadings postulated by Crutzen in 2006 and by Rasch, Crutzen and Coleman in 2008. It is important to understand these differences as they get blurred and confused by people trying to interpret the requirements of a stratospheric aerosol program. In his 2006 paper, Crutzen assumed that the aerosol formed would have the same radius as that from Mt. Pinatubo's aerosol. This was around 0.47 micron. In that case, 1-2Tg of sulfur added per year would accumulate to produce a level of 1.9Tg which would be enough to offset the loss in tropospheric aerosol from SO2 pollution. To offset a doubling of CO2, he calculated that 4Tg would have to be added per year, accumulating to a stable level of 5.3Tg. The increase to a larger level than the amount added per year is due to the fact that not all of the aerosol exits the stratosphere in 12 months. It tends to follow what is known as an e-folding pattern in which 63% leaves after 1 year and 63% of what remains leaves after the second year, etc. Of course, the altitude and latitude of the aerosol will also determine the lifetime, so these figures are estimates, not guarantees. In the 2008 Rasch et al. paper, the aerosol was assumed to be more like the background aerosol, 0.17 micron in radius and would therefore, require much less precursor to be added each year as it would have a longer lifespan and would also be more efficient at scattering sunlight. To offset a doubling of CO2, 1.5Tg would have to be added per year, resulting in a stratospheric level of 2.4-5.5Tg. I don't remember the reason for the range, except it may have been because as the stratospheric burden gets large enough, the aerosol starts absorbing significant amounts of IR from the surface and thus more is required to maintain the radiative offset. If the background sized aerosol could be produced, this would greatly reduce the quantities of precursor required for transport to the stratosphere. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
