I've followed up with a little more research into atmospheric aerosols, black carbon in particular, and find references that seem to indicate a mean particle size of under one micron for BC particles (0.2 microns) that are lofted into the atmosphere and thus can be transported long distances. I want to make sure I understand the context of this issue.
http://www.pnas.org/content/100/11/6319.full#xref-ref-13-1 http://www.agu.org/pubs/crossref/2000/2000JD900240.shtml In our biochar preparation procedure, we aim for a particle size of about 2 millimeters. There are some smaller particles mixed in, but we certainly don't micronize the char. Some feedstock materials will produce smaller particles, but they certainly won't have a mean size of less than one micron. Once the char enters the soil, it has been demonstrated that it tends to break down into smaller particles, but as I indicated earlier, these tend to form aggregates in a similar manner that organic carbon forms aggregates in soil. I've seen this happen, and worked the clumpy textured material, very much like good black soil, in my hands. Soil dust also has a radiative forcing, and it originates particularly in arid areas of the world like the Sahara desert. Biochar will be added to agricultural soils, not to deserts. Although wind erosion lifts some agricultural soil aloft, it seems likely that this is not the main source of dust in the atmosphere. It also seems logical that because the amount of biochar added to soil is of such a low percentage, the (aggregated) char mixed into any soil dust that ends up in the atmosphere will not increase the radiative forcing of soil dust. Simply put, if our agricultural soils were dry enough and exposed enough to be major contributors to atmospheric soil dust, we couldn't grow any food on them. On a practical basis, we find moist char much easier to work with. Quenching keeps the hot char from igniting as it comes out of the kiln, which is much easier than keeping it from being exposed to oxygen. The dust that can occur from working with the char is a health hazard. I can personally attest to the fact that even a single day's exposure to char dust is a significant challenge for the lungs to deal with. What am I missing that would indicate that biochar production and incorporation may be likely to cause an increase in atmospheric black carbon content? I don't see it. In fact, the opposite seems more plausible to me: Agricultural productivity increases from biochar could cause a decrease in slash and burn shifting agriculture. The use of biochar producing cookstoves, such as that from WorldStove, could cause a decrease in open fire biomass burning. The energy derived from large scale pyrolysis systems could displace fossil fuel use. Reduced fertilizer usage could reduce the fossil fuels used to produce and transport them. The burning of agricultural waste because it is deemed the most economical way to deal with it is replaced by the production of biochar and energy from pyrolysis because it provides an income stream, all of which would likely cause a decrease in atmospheric BC levels, perhaps a very significant decrease if adopted at a large scale. Again, I could be missing an important detail. Please let me know if you see something I've glossed over. Kind regards, Nando Nando M. Breiter The CarbonZero Project CP 234 6934 Bioggio Switzerland +41 91 600 0335 [email protected] www.carbonzero.ch -- 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.
