A laboratory comparison of the global warming impact of five major types of biomass cooking stoves Nordica MacCarty, Damon Ogle, and Dean Still Aprovecho Research Center, 79093 Highway 99, Cottage Grove, OR, USA E-mail (MacCarty): nordica.maccarty@gmail.com Tami Bond and Christoph Roden Department of Civil and Environmental Engineering, University of Illinois, Urbana-Champaign Newmark Civil Engineering Laboratory, MC-250, 205 N. Mathews Ave., Urbana, IL 61801, USA With over 2 billion of the world’s population living in families using biomass to cook every day, the possibility of improved stoves helping to mitigate climate change is generating increasing at- tention. With their emissions of CO2, methane, and black carbon, among other substances, is there a cleaner, practical option to provide to the families that will need to continue to use biomass for cooking? This study served to help quantify the relative emissions from five common types of biomass combustion in order to investigate if there are cleaner options. The laboratory results showed that for situations of sustainable harvesting where CO2 emissions are considered neutral, some improved stoves with rocket-type combustion or fan assistance can reduce overall warming impact from the products of incomplete combustion (PICs) by as much as 50-95%. In non-sustainable situations where fuel and CO2 savings are of greater importance, three types of improved combustion methods were shown to potentially reduce warming by 40-60%. Charcoal-burning may emit less CO2 than traditional wood-burning, but the PIC emissions are significantly greater. Key-words: improved cookstoves, global warming, carbon dioxide, methane, soot, black carbon, products of incomplete combustion, sustainable harvesting, biomass 1. Background While much of the recent work in the cook stove com- munity has been focused on the potential health benefits of improved stoves, data is emerging supporting possible benefits that improved cook stoves could have for the health of the climate as well. Some of the major green- house gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), are present in the emis- sions from biomass cooking stoves. Particulate matter emissions from traditional biomass cooking stoves are also significant and have strong and visible effects on the climate. An August 2007 headline in the online BBC News stated “Clouds of pollution over the Indian Ocean appear to cause as much warming as greenhouse gases released by human activity” [BBC, 2007]. These clouds are composed primarily of soot, or black carbon particles. A similar article in the Scientific American stated “The dominant source for all this black carbon is cooking fires” [Biello, 2007]. A later article in Nature Geoscience [Ramanathan and Carmichael, 2008], summarized in the New York Times [Revkin, 2008], showed the contribution of cooking fires on the overall Asian black carbon con- centrations, as shown in [Adhikary et al., 2007]. Further, studies are showing that the soot particles, which enhance the solar absorption by snow and ice, are contributing to the ice melt in the Himalayas and the retreat of Arctic sea ice [Flanner et al., 2007]. Reduction of soot emissions can show a more immediate effect on halting climate change than reducing the longer-lived emissions of CO 2 only. Just how much gaseous pollutants and black carbon do cooking stoves emit and are there feasible biomass com- bustion options that can help to reduce emissions from traditional cooking methods? The emissions from five cooking stoves were measured by a team of researchers from the Aprovecho Research Center, the University of Illinois Urbana-Champaign, and at Colorado State Uni- versity. The stoves were tested in an effort to examine four common methods of wood combustion: open burn- ing, “rocket” combustion chamber-type combustion, gasi- fication, and forced draft. The emissions from a common charcoal stove were also investigated. 1.1. Sustainable vs. non-sustainable harvesting of biomass The manner in which fuel is harvested has a large influ- ence on the climate change potential when cooking with biomass. If biomass is harvested sustainably, the CO2 re- leased in combustion is theoretically reabsorbed by the biomass growing to replace it. If biomass is not har- vested sustainably, then the CO2 released when the Energy for Sustainable Development • Volume XII No. 2 • June 2008 Articles 56