Unvented Rocket stove reduced PM2.5 by an average of 48% in field studies
Modelled 24-hour PM2.5 concentrations derived from field-based emissions rates of the rocket stove (which should be more comparable to observed levels of air pollution than laboratory-based rates), had a mode of around 500 μg/m3, a reduction of around 300 μg/m3, or nearly 40% compared to the traditional chulha. CO emissions were reduced from a mode of around 11 mg/m3 to 5 mg/m3, or by around 55%; this concentration of CO for the rocket stove (5 mg/m3) lies below the WHO 24-hour AQG.
The review of intervention impacts (see Review 6) found that this type of stove (Rocket) reduced PM2.5 by an average of 260 μg/m3 and CO by 3.41 ppm (3.9 mg/m3), with weighted mean percentage reductions of 48% and 39% respectively, and post intervention means of 410 μg/m3 and 6.6 ppm (7.6 mg/m3) respectively. Given the variability in data, devices, fuel used and other factors, these results can be considered consistent.
Chimneys: largest reductions in emission levels of all stoves and fuels
On average… it is expected that emissions entering the room from vented stoves are 75% lower than with unvented stoves. The review of intervention impacts (see Review 6) found that solid fuel stoves with chimneys (for which there were 23 and 22 estimates for PM2.5 and CO respectively) did indeed achieve a greater reduction of PM2.5 and CO than unvented stoves. This reduction was 63% for both pollutants, with post-intervention means of 370 μg/m3 and 4.2 ppm (4.8 mg/m3) for PM2.5 and CO respectively.
It should be noted, however, that several of the chimney-stove studies reported the largest reductions in emission levels of all stoves and fuels studied in the review (see Review 6). Three such studies reported PM2.5 levels of between 50 and 80 μg/m3 post-intervention, which are more consistent with the larger reductions predicted by the model.
These findings do not undermine the model but point towards reasons why this much better performance is not being achieved more widely. As discussed above, other sources in the home and AAP are likely to be responsible.
The WHO 2014 Indoor Air Quality Guidelines for Household Fuel Combustion may be downloaded here.