Very interesting subject of course. Much work has been done on this subject in South Africa where the ash content of domestic coal if far higher than Nalaikh, for example. Nalaikh provides about 60% of domestic coal in UB. My point about SO2 is that it is an inherent emission, like uranium or thorium. If you burn less, you get less. Thus the thermal efficiency of the stoves is critical. Also, if a stove burns more constantly at a lower power, it feels the same to the occupant. This means a 5 kW stove that burns continuously feels the same as a 25 kW stove that roars then dies out rapidly. Recent developments on this score are very positive. It is possible to greatly reduce the amount of coal burned per ger-dweller with better stove technologies as has been demonstrated at the Stove Emissions and Efficiency Testing Laboratory in UB (SEET Lab). It is critical that those getting involved in stove emissions gain some depth before jumping in with advice about which emissions are dangerous and which are more dangerous. It is sometimes not obvious: If a stove produces 'lower SO2' it usually means it is making H2S instead which is the 'stink' of coal. It is caused by poor combustion of Sulphur. It is not usual to measure H2S in air quality assessments and major errors in technology selection can be made as a result. Perfect combustion produces SO2 not H2S. Nalaikh (in fact all Mongolian coals) have a very low Sulphur content which is a big plus. That is why people want to export it. Power stations scrub it out and sell it. Non-inherent emissions include the particulate matter(PM)produced by stoves which is a consequence of poor combustion, not coal composition, despite what is often said. PM we can do someting about. Stoves are now in use in UB that have 1/1000th of the PM emissions of a poor conditon traditional stove operated in a traditional manner. However the SO2 per kg may go up! This is because of the conversion of really dangerous H2S to much less dangerous SO2. The view must be holistic, as wisely stated above by Robin. Management of risk means all risks, not 'popular' ones. So, using a stove that uses 50% less coal, burned with >90% less PM makes a very big difference to the air quality problem. For those who want to look into the Radon problem (I thought it had been examined by NUM?) please keep two things in mind about the ger dwellers exposure. The air changes per hour rating for a ger is 50 ac/h - a gigantic turnover. A stove also pulls into the home about 50-100 cubic metres per hour and sends it up the chimney. This is a large and continuous ventilation often overlooked. I would like the conversation to include more numbers for exposure as tha above is pretty theoretical. There are people in UB who are well versed on this including the staff at NRC at NUM. The ac/h is very high by any standard. The experience of dealing with radon in Port Hope Ontario, Canada (major radon event) shows that ventilation (heat exchanging air ducting) reduces the exposure to international standards. A ger is very breezy all the time and most people overlook the stove as a ventilator. In winter the stove takes in more air and that air comes from the ger which comes from outside! Air quality inside the ger is reduced by outside air pulled in! The situation is that bad. I look forward to comparisons of modern buildings to gers. Concrete is radioactive at some level, particularly the aggregate. Granite is radioactive too... Regards Crispin Contact via ADB-UB.