Clean Cookstove Emissions: How Are They Now and How Low Do They Need To Go?

Improved cookstoves offer potential reductions in fuel use and pollutants’ health and climate impacts. This talk presents evidence that most current ‘improvements’ are insufficient to provide the promised health and climate benefits. A simple, extensible analytical framework is used to compare stove options across multiple impacts (health; climate) and quantify the potential co-benefits from upgraded fuel and stove combinations. The stove-fuel types considered include basic ‘unimproved’ use of biomass and coal, improved biomass cookstoves ranging from basic to more advanced models with and without chimneys, and stoves using ‘modern’ fuels like LPG and kerosene. Health impacts are quantified via estimated personal PM intake and a recently proposed log-linear intake-response relationship applicable to PM concentrations well above typical urban levels. Climate impacts are estimated using the global warming commitment on a 100 year time horizon (GWC), which gives a conservative (low) estimate of the short-term climate impacts of stove emissions. The results indicate that health and climate impacts span 2 orders of magnitude among the technologies considered. Indoor air pollution is heavily impacted by combustion performance and ventilation; climate impacts are influenced by combustion performance and fuel properties including biomass renewability. Emission components not included in current carbon trading schemes, such as black carbon particles and carbon monoxide, contribute a large proportion of the total climate impact.  Multiple ‘improved’ stove options analyzed in this paper yield roughly equivalent climate benefits but have different impacts on indoor air pollution. Improvements to biomass stoves can reduce indoor air pollution, which nonetheless remains significantly higher than for stoves that use liquid and gaseous hydrocarbons.  LPG- and kerosene-fueled stoves have unrivaled air quality benefits and their climate impacts are also lower than all but the cleanest stoves using renewable biomass. This analysis is bolstered with recent data from in-use emission testing of traditional and improved (‘Rocket’-type) stoves with and without chimneys in rural India. For the promised benefits of cookstove programs to be realized, stove technologies and programs must take approaches that drop emission levels and exposures to match those currently only attainable with ‘modern’ fuels. Global efforts need to move forward based on honest assessments of what current approaches can achieve and set goals based on data, not wishful thinking.