Breathing zone and plume zone. Credit: ACS, Kar et al. Click to enlarge.

Abhishek Kar, Hafeez Rehman, Jennifer Burney and colleagues from The Energy and Resources Institute, New Delhi; Scripps Institution of Oceanography, University of California, San Diego; and the Center for Embedded Sensor Networking, University of California, Los Angeles, explain that hundreds of millions of people in developing countries in South Asia, Africa and South America are exposed to soot from mud stoves and 3-stone fires used for cooking, heating and light. The particles can be inhaled deeply into the lungs and have been linked to health problems similar to those associated with cigarette smoking.

In addition, black soot released into the atmosphere is a major factor in global warming. Aid agencies and governments have been seeking replacements for traditional cookstoves and fires to remedy those problems, with ICs as one of the leading hopes. Until now, however, there have been little real-world data on the actual performance of ICs.

ICs encompass a range of technologies, they noted, including natural draft (ND) stoves, which feature structural modifications to enhance air flow, and forced draft (FD) stoves, which additionally employ an external fan to force air into the combustion chamber.

Comparison of BC concentrations for hardwood and mixed fuel tests in (left) the breathing zone, and (right) the plume zone. In this plot, a red star under the boxes means that the mean values for hardwood and mixed fuel tests are statistically different for that stove technology class (at the 95% confidence level, p < 0.05). Credit: ACS, Kar et al. Click to enlarge.

The researchers measured black carbon concentrations from five commercial IC models and a traditional mud cookstove. They did the test in real homes as part of Project Surya, which quantifies the impacts of cleaner cooking technologies in a village in India. These experiments revealed four significant findings about the tested stoves, the authors said:

1. FD stoves emerge as the superior IC technology, reducing plume zone BC concentration by a factor of 4 (compared to 1.5 for ND). Indoor cooking-time BC concentrations, which varied from 50 to 1000 μg m⁻³ for the traditional mud cookstove, were reduced to 5−100 μg m⁻³ by the top-performing FD stove.

2. BC reductions from IC models in the same technology category vary significantly: for example, some ND models occasionally emit more BC than a traditional cookstove. Within the ND class, only microgasification stoves were effective in reducing BC.

3. BC concentration varies significantly for repeated cooking cycles with same stove (standard deviation up to 50% of mean concentration) even in a standardized setup, highlighting inherent uncertainties in cookstove performance.

4. Use of mixed fuel (reflective of local practices) increases plume zone BC concentration (compared to hardwood) by a factor of 2 to 3 across ICs.

The variation in performance among the five ICs tested in this study should raise caution about IC assumptions and terminology, particularly as some so-called “improved” stoves in the natural draft category may at times perform even worse than a traditional mud cookstove. Across metrics, FD stoves outperform ND stoves in terms of reduction in BC concentrations. FD stoves should be considered for dissemination as improved cookstove programs worldwide begin to consider climate metrics as selection criteria.

...Our results also have significant implications for health and climate impact studies, as impact estimates based on ND stoves would underestimate the BC reduction potential from ICs. In this regard, this study highlights the need for repeated tests to confirm statistical significance of mitigation potential.

—Kar et al.

The researchers acknowledge funding from private donors, the National Science Foundation, the Swedish International Development Agency, the United Nations Environment Programme, the Vetlesen Foundation and the Alderson Foundation.

Resources

• Abhishek Kar, Ibrahim H. Rehman, Jennifer Burney, S. Praveen Puppala, Ramasubramanyaiyer Suresh, Lokendra Singh, Vivek K. Singh, Tanveer Ahmed, Nithya Ramanathan, and Veerabhadran Ramanathan (2012) Real-Time Assessment of Black Carbon Pollution in Indian Households Due to Traditional and Improved Biomass Cookstoves. Environmental Science & Technology 46 (5), 2993-3000 doi: 10.1021/es203388g