WHO GUIDELINES FOR INDOOR AIR QUALITY: HOUSEHOLD FUEL COMBUSTION, World Health Organization, Geneva, 2014
We contributed, along with many other participants, in the review and assessment of the HAP evidence base for developing guidelines for stove emissions for PM2.5 and CO such that the 2005 WHO Air Quality Guidelines can be maintained in households. These Indoor AQGs were released in November 2014, which marked the first time in human history, when it will no longer be possible to claim a stove is truly "improved" or "clean" without reference to authoritative global set of health-based guidelines.
This is the third, and last currently planned, volume from WHO on IAQ, the first two being on Selected Individual Pollutants and Dampness and Mold. It is the result of 3+ years of work by an international expert committee and many peer reviewers including a year-long internal WHO process of quality checking and reframing to be consistent with other WHO guideline documents,
This third volume is a bit different in its recommendations than most other WHO guidelines in that it does not develop new exposure/concentration guidelines for the critical pollutants themselves, but takes these for CO from the previous IAQ document on Selected Pollutants and for PM2.5 from the 2005 WHO Air Quality Guidelines (AQGs). In addition to extensive reviews of the literature, this new document presents recommended guidelines for indoor emissions limits that will keep a large fraction of households below the AQGs themselves for CO and PM2.5. As there are wide ranges of household sizes, ventilation rates, and cooking patterns, it specifies limits in a probabilistic manner using a Monte Carlo model, e.g., to keep 90% of household below the AQG, the emissions needs to be below X, for 50% they need to be below y.
Notably, this document formalizes what was only stated conceptually in the 2005 AQGs, which is that the guidelines should apply in every non-occupational micro-environment where people spend significant time -- indoor or outdoor.
The document also addresses chimney stoves as well as having sections on coal and kerosene as household fuels -- discouraging both because of apparent extra toxicities of their emissions.
The quantitative recommendations will be a challenge to the biomass stove community in that, in keeping with the health evidence, truly low emission rates of unvented stoves will be needed to protect health adequately. It is planned that the ongoing process of creating stove standards under the ISO process will adopt these recommendations, as was agreed previously. Newer evidence since 2005 on the health effects of combustion air pollution, as for example found in the latest Global Burden of Disease estimates, would indicate that when the next revision of the AQGs is done (as now planned), the limits will become even lower. The stove community thus should probably therefore consider what this document recommends as likely to tighten further over time.