Keel, I'm no scientist so I can only go by what I read. And I've read just about everything on the subject that I can find.
No; it's not carbon negative. It's "considered" carbon negative because you end up with charcoal. That does not mean that there was not a chemical reaction that released gasses and particulate matter. I'm not saying there is anything wrong with what you are doing (tilling carbon back in to your garden); but to say it results in less pollution is a bit misleading. There are still emissions related to the pyrolysis and I don't think tars, particulates, and methanes are things you want to be breathing in every day when you cook dinner.
"Design with the correct secondary air flow ensures
near-stoichiometric combustion that allows attainment of peak combustion temperatures with accompanying
high water boiling efficiencies (up to 50% for vessels of practical relevance) and very
low emissions (of carbon monoxide, particulate matter and oxides of nitrogen)."
"Paul’s TLUD stoves have been tested and shown to produce very low emissions of CO and particulates."
5 Gallon (22-liter) TLUD Stove for Biochar | BioEnergy Lists: BioChar (or Terra Preta)
"Recognized as a “carbon neutral” initiative; In fact would be "carbon negative
" when the charcoal is dumped back into the soil."
TLUD Gasifier Stoves - A wood stove with a difference | Servals Automation Pvt Ltd
This last site has a chart at the bottom that shows carbon monoxide and particulate matter emissions for various stoves, but it's so small I can't read it.
I don't mean to hijack this thread. But I think this is relevant and important. Perhaps less so for the developed world, but the technology could potentially save many lives in the third world. As well as improving crop yields and improving soil fertility and sustainability.
"Respiratory infections caused by smoke from indoor cooking fires common in the Third World could be reduced drastically through the use of inexpensive, more efficient stoves and modestly cleaner fuels, according to researchers at the University of California, Berkeley, and Princeton University who monitored illness and pollution levels for three years in a Kenyan village."
University of California - UC Newsroom | Reducing Respiratory Illness from Indoor Cooking Fires in Third World