How to characterize emission factors?
Tami Bond, Bond Research Group, University of Illinois Urbana-Champaign February 2006
How to characterize emission factors? Short story:
- For traditional stoves, we have some, they vary a lot, and we don't always know why they vary. It's probably a combination of wood, moisture, and practice, and who knows what else.
- For improved stoves, we have a few from Aprovecho's work, from Kirk Smith's work, and a very few from our Honduras measurements. Trouble is, 'improved' means a whole lot of things, from a mud stove with a specific shape to a stove with insulated combustion chamber and chimney. There may be nearly as many improved stoves (and emission factors) as there are improvers... although with Internet dissemination, perhaps they will start converging to best practices.
- For stoves that have significantly altered the air flow (e.g.
gasification, controlled secondary air), there are very few measurements, and the ones Paul A. cites from Stoves camp are the only ones I know of.
We expect that this situation of few emission factors will change as measurements become more widely available. Aprovecho's lab is a start, but that needs to be replicated in more than one region. Tom Miles would perhaps like to see emission factors 'like industry'-- I hope that they can be *better*. In fact, emission factors from industry, vehicles, etc.
have a lot of uncertainty despite all the measurements (and money) that have supported them. This is not because they were done poorly; it's because practice makes quite a lot of difference. It's hard to get people (boiler owners, drivers, cooks) to replicate actual practice when you are watching, and to take a representative sample of that variable practice.
In addition to 'more measurements', gaps to be addressed include:
- Field versus lab. We're finding that the PM from traditional Honduran cookstoves is far higher than we expected. Is it the wood? Or more high-power use?
- We have so far measured only PM and CO. We have not focused on NOx, because NOx is (mainly) made by high-temperature applications, and we think stoves run at low temperature. As combustion gets better, that assumption may become worse, and NOx should be measured. We also need a way to measure methane and non-methane organic coumpounds in the field, if anyone wants to consider GHG credits or air quality benefits.
I might also ask why and how well we need to know emission factors. In general, we need to assure ourselves that interventions or improvements are really improvements, and that the benefit does not disappear if somebody operates the device incorrectly but reasonably, or uses a fuel that's widely available, and so on. For some purposes, it may be enough to know that you get a certain percentage reduction and that it is robust under reasonable conditions. For other purposes (like mine) one may want to know magnitudes from different stoves, regions and fuels.
All for now, but please continue the discussion.
Dept. of Civil & Environmental Engineering University of Illinois, Urbana-Champaign Newmark Civil Engineering Laboratory, MC-250
205 N. Mathews Ave.
Urbana, IL 61801
Reply to Frans:
Of course one can measure very small concentrations of methane or other hydrocarbons in the lab, with GCMS, FTIR and the like. But it is difficult to take these to the field, and they are not affordable for the average stove designer. We are working on providing measurements that many people can use. We have spent some time looking for sensors for methane and HC. The other end of your scale is occupied by people who measure methane in natural gas. These are the right price but not the right concentration for our purposes.
I agree with you that PAH (as we call in English) are hazardous. We think these can be measured in the lab-- for measurements we are working on, the main goal is to give stove designers, NGOs, etc tools to tell when they have reduced CO, PM and maybe total HC. We think that if they have done that, they have probably reduced total PAH as well.
I would let the others comment on electrostatic precipitators-- whether there is enough electricity to run them, and whether they could be cheap enough to install on a stove that needs to cost $5.