The assessment chapter provides an accessible entry into a problem of major global importance for both health and environmental sustainability.

As discussed in Larsen's chapter, there are a number of important challenges with setting targets related to HAP. Unfortunately, the technological solutions proposed do not properly address the issues because they may have undesirable side effects and because air quality and the costs and benefits of specific changes vary considerably across households and locations. Thus, it is puzzling that this important variation does not figure in the subsequent benefit-cost analysis of clean cooking interventions, which instead looks like an analysis based on hypothetical air quality (not technology-based) targets.

The most striking omission is a significant discussion of the role and implications of behavior. In practice, individual decisions to invest in preventive health or environmental improvements involve a rational trade-off with consumption of other goods and leisure. But people often make decisions that would seem to endanger their well-being, sometimes because they misunderstand the risks they face. Also, because of the nonlinear response to air pollution, a relatively large investment may not be enough to deliver substantial health benefits.

Existing work supports the idea that there is something households and individuals like about traditional stoves. The study also ignores the fact that strikingly few households who obtain a cleaner biomass stove end up using it exclusively. In fact, surprisingly little is known at this time about how to induce the behavior change that effectively delivers long-term benefits. As such, setting technology-based targets creates a risk that policies designed to reach them will repeat the hard failures of related domains (e.g., water and sanitation, and malaria prevention), which generally failed to incentivize the pursuit of locallyresponsive and desired solutions. Making prescriptive recommendations about the specific stoves that people should or should not own will likely result in dissemination of large numbers of stoves that households do not want or use.

Behavior may also change and reduce the costeffectiveness of interventions. In the case of clean stove promotion, one example of this type of behavioral feedback would be if household members increase the amount of time spent and cooking done indoors, thereby offsetting anticipated reductions in harmful exposures.